[PATCH bpf-next v3 00/12] BPF Standard Streams

[PATCH bpf-next v3 00/12] BPF Standard Streams

[Kumar Kartikeya Dwivedi]

This set introduces a standard output interface with two streams, namely
stdout and stderr, for BPF programs. The idea is that these streams will
be written to by BPF programs and the kernel, and serve as standard
interfaces for informing user space of any BPF runtime violations. Users
can also utilize them for printing normal messages for debugging usage,
as is the case with bpf_printk() and trace pipe interface.

BPF programs and the kernel can use these streams to output messages.
User space can dump these messages using bpftool.

The stream interface itself is implemented using a lockless list, so
that we can queue messages from any context. Every printk statement into
the stream leads to memory allocation. Allocation itself relies on
try_alloc_pages() to construct a bespoke bump allocator to carve out
elements. If this fails, we finally give up and drop the message.

See commit logs for more details.

Two scenarios are covered:
 - Deadlocks and timeouts in rqspinlock.
 - Timeouts for may_goto.

In each we provide the stack trace and source information for the
offending BPF programs. Both the C source line and the file and line
numbers are printed. The output format is as follows:

ERROR: AA or ABBA deadlock detected for bpf_res_spin_lock
Attempted lock   = 0xff11000108f3a5e0
Total held locks = 1
Held lock[ 0] = 0xff11000108f3a5e0
CPU: 48 UID: 0 PID: 786 Comm: test_progs
Call trace:
bpf_stream_stage_dump_stack+0xb0/0xd0
bpf_prog_report_rqspinlock_violation+0x10b/0x130
bpf_res_spin_lock+0x8c/0xa0
bpf_prog_3699ea119d1f6ed8_foo+0xe5/0x140
  if (!bpf_res_spin_lock(&v2->lock)) @ stream_bpftool.c:62
bpf_prog_9b324ec4a1b2a5c0_stream_bpftool_dump_prog_stream+0x7e/0x2d0
  foo(stream); @ stream_bpftool.c:93
bpf_prog_test_run_syscall+0x102/0x240
__sys_bpf+0xd68/0x2bf0
__x64_sys_bpf+0x1e/0x30
do_syscall_64+0x68/0x140
entry_SYSCALL_64_after_hwframe+0x76/0x7e

ERROR: Timeout detected for may_goto instruction
CPU: 48 UID: 0 PID: 786 Comm: test_progs
Call trace:
bpf_stream_stage_dump_stack+0xb0/0xd0
bpf_prog_report_may_goto_violation+0x6a/0x90
bpf_check_timed_may_goto+0x4d/0xa0
arch_bpf_timed_may_goto+0x21/0x40
bpf_prog_3699ea119d1f6ed8_foo+0x12f/0x140
  while (can_loop) @ stream_bpftool.c:71
bpf_prog_9b324ec4a1b2a5c0_stream_bpftool_dump_prog_stream+0x7e/0x2d0
  foo(stream); @ stream_bpftool.c:93
bpf_prog_test_run_syscall+0x102/0x240
__sys_bpf+0xd68/0x2bf0
__x64_sys_bpf+0x1e/0x30
do_syscall_64+0x68/0x140
entry_SYSCALL_64_after_hwframe+0x76/0x7e

Changelog:
----------
v2 -> v3
v2: https://lore.kernel.org/bpf/20250524011849.681425-1-memxor@gmail.com

 * Fix bug when handling single element stream stage. (Eduard)
 * Move to mutex for protection of stream read and copy_to_user(). (Alexei)
 * Split bprintf refactor into its own patch. (Alexei)
 * Move kfunc definition to common_btf_ids to avoid initcall proliferation. (Alexei)
 * Return line number by reference in bpf_prog_get_file_line. (Alexei)
 * Remove NULL checks for BTF name pointer. (Alexei)
 * Add WARN_ON_ONCE(!rcu_read_lock_held()) in bpf_prog_ksym_find. (Eduard)
 * Remove hardcoded stream stage from macros. (Alexei, Eduard)
 * Move refactoring hunks to their own patch. (Alexei)
 * Add empty opts parameter for future extensibility to libbpf API. (Andrii, Eduard)
 * Add BPF_STREAM_{STDOUT,STDERR} to UAPI. (Andrii)
 * Add code to match on backtrace output. (Eduard)
 * Fix misc nits.
 * Add acks.

v1 -> v2
v1: https://lore.kernel.org/bpf/20250507171720.1958296-1-memxor@gmail.com

 * Drop arena page fault prints, will be done as follow up. (Alexei)
 * Defer Andrii's request to reuse code and Alan's suggestion of error
   counts to follow up.
 * Drop bpf_dynptr_from_mem_slice patch.
 * Drop some acks due to heavy reworking.
 * Fix KASAN splat in bpf_prog_get_file_line. (Eduard)
 * Collapse bpf_prog_ksym_find and is_bpf_text_address into single
   call. (Eduard)
 * Add missing RCU read lock in bpf_prog_ksym_find.
 * Fix incorrect error handling in dump_stack_cb.
 * Simplify libbpf macro. (Eduard, Andrii)
 * Introduce bpf_prog_stream_read() libbpf API. (Eduard, Alexei, Andrii)
 * Drop BPF prog from the bpftool, use libbpf API.
 * Rework selftests.

RFC v1 -> v1
RFC v1: https://lore.kernel.org/bpf/20250414161443.1146103-1-memxor@gmail.com

 * Rebase on bpf-next/master.
 * Change output in dump_stack to also print source line. (Alexei)
 * Simplify API to single pop() operation. (Eduard, Alexei)
 * Add kdoc for bpf_dynptr_from_mem_slice.
 * Fix -EINVAL returned from prog_dump_stream. (Eduard)
 * Split dump_stack() patch into multiple commits.
 * Add macro wrapping stream staging API.
 * Change bpftool command from dump to tracelog. (Quentin)
 * Add bpftool documentation and bash completion. (Quentin)
 * Change license of bpftool to Dual BSD/GPL.
 * Simplify memory allocator. (Alexei)
   * No overflow into second page.
   * Remove bpf_mem_alloc() fallback.
 * Symlink bpftool BPF program and exercise as selftest. (Eduard)
 * Verify output after dumping from ringbuf. (Eduard)
 * More failure cases to check API invariants.
 * Remove patches for dynptr lifetime fixes (split into separate set).
 * Limit maximum error messages, and add stream capacity. (Eduard)

Kumar Kartikeya Dwivedi (12):
  bpf: Refactor bprintf buffer support
  bpf: Introduce BPF standard streams
  bpf: Add function to extract program source info
  bpf: Ensure RCU lock is held around bpf_prog_ksym_find
  bpf: Add function to find program from stack trace
  bpf: Add dump_stack() analogue to print to BPF stderr
  bpf: Report may_goto timeout to BPF stderr
  bpf: Report rqspinlock deadlocks/timeout to BPF stderr
  libbpf: Add bpf_stream_printk() macro
  libbpf: Introduce bpf_prog_stream_read() API
  bpftool: Add support for dumping streams
  selftests/bpf: Add tests for prog streams

 arch/x86/net/bpf_jit_comp.c                   |   1 -
 include/linux/bpf.h                           |  80 ++-
 include/uapi/linux/bpf.h                      |  24 +
 kernel/bpf/Makefile                           |   2 +-
 kernel/bpf/core.c                             | 105 +++-
 kernel/bpf/helpers.c                          |  29 +-
 kernel/bpf/rqspinlock.c                       |  23 +
 kernel/bpf/stream.c                           | 529 ++++++++++++++++++
 kernel/bpf/syscall.c                          |  27 +-
 .../bpftool/Documentation/bpftool-prog.rst    |   7 +
 tools/bpf/bpftool/bash-completion/bpftool     |  16 +-
 tools/bpf/bpftool/prog.c                      |  49 +-
 tools/include/uapi/linux/bpf.h                |  24 +
 tools/lib/bpf/bpf.c                           |  20 +
 tools/lib/bpf/bpf.h                           |  21 +
 tools/lib/bpf/bpf_helpers.h                   |  16 +
 tools/lib/bpf/libbpf.map                      |   1 +
 .../testing/selftests/bpf/prog_tests/stream.c | 140 +++++
 tools/testing/selftests/bpf/progs/stream.c    |  75 +++
 .../testing/selftests/bpf/progs/stream_fail.c |  17 +
 20 files changed, 1183 insertions(+), 23 deletions(-)
 create mode 100644 kernel/bpf/stream.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/stream.c
 create mode 100644 tools/testing/selftests/bpf/progs/stream.c
 create mode 100644 tools/testing/selftests/bpf/progs/stream_fail.c


base-commit: 3ce7cdde66e65a400b2d1b2a7f72c499e1db26b6
-- 
2.47.1

[PATCH bpf-next v3 01/12] bpf: Refactor bprintf buffer support

[Kumar Kartikeya Dwivedi]

Refactor code to be able to get and put bprintf buffers and use
bpf_printf_prepare independently. This will be used in the next patch to
implement BPF streams support, particularly as a staging buffer for
strings that need to be formatted and then allocated and pushed into a
stream.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf.h  | 15 ++++++++++++++-
 kernel/bpf/helpers.c | 26 +++++++++++---------------
 2 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5dd556e89cce..4fff0cee8622 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3550,6 +3550,16 @@ bool btf_id_set_contains(const struct btf_id_set *set, u32 id);
 #define MAX_BPRINTF_VARARGS		12
 #define MAX_BPRINTF_BUF			1024
 
+/* Per-cpu temp buffers used by printf-like helpers to store the bprintf binary
+ * arguments representation.
+ */
+#define MAX_BPRINTF_BIN_ARGS	512
+
+struct bpf_bprintf_buffers {
+	char bin_args[MAX_BPRINTF_BIN_ARGS];
+	char buf[MAX_BPRINTF_BUF];
+};
+
 struct bpf_bprintf_data {
 	u32 *bin_args;
 	char *buf;
@@ -3557,9 +3567,12 @@ struct bpf_bprintf_data {
 	bool get_buf;
 };
 
-int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
+int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
 			u32 num_args, struct bpf_bprintf_data *data);
 void bpf_bprintf_cleanup(struct bpf_bprintf_data *data);
+int bpf_try_get_buffers(struct bpf_bprintf_buffers **bufs);
+void bpf_put_buffers(void);
+
 
 #ifdef CONFIG_BPF_LSM
 void bpf_cgroup_atype_get(u32 attach_btf_id, int cgroup_atype);
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index b71e428ad936..67d48f9fb173 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -763,22 +763,13 @@ static int bpf_trace_copy_string(char *buf, void *unsafe_ptr, char fmt_ptype,
 	return -EINVAL;
 }
 
-/* Per-cpu temp buffers used by printf-like helpers to store the bprintf binary
- * arguments representation.
- */
-#define MAX_BPRINTF_BIN_ARGS	512
-
 /* Support executing three nested bprintf helper calls on a given CPU */
 #define MAX_BPRINTF_NEST_LEVEL	3
-struct bpf_bprintf_buffers {
-	char bin_args[MAX_BPRINTF_BIN_ARGS];
-	char buf[MAX_BPRINTF_BUF];
-};
 
 static DEFINE_PER_CPU(struct bpf_bprintf_buffers[MAX_BPRINTF_NEST_LEVEL], bpf_bprintf_bufs);
 static DEFINE_PER_CPU(int, bpf_bprintf_nest_level);
 
-static int try_get_buffers(struct bpf_bprintf_buffers **bufs)
+int bpf_try_get_buffers(struct bpf_bprintf_buffers **bufs)
 {
 	int nest_level;
 
@@ -794,16 +785,21 @@ static int try_get_buffers(struct bpf_bprintf_buffers **bufs)
 	return 0;
 }
 
-void bpf_bprintf_cleanup(struct bpf_bprintf_data *data)
+void bpf_put_buffers(void)
 {
-	if (!data->bin_args && !data->buf)
-		return;
 	if (WARN_ON_ONCE(this_cpu_read(bpf_bprintf_nest_level) == 0))
 		return;
 	this_cpu_dec(bpf_bprintf_nest_level);
 	preempt_enable();
 }
 
+void bpf_bprintf_cleanup(struct bpf_bprintf_data *data)
+{
+	if (!data->bin_args && !data->buf)
+		return;
+	bpf_put_buffers();
+}
+
 /*
  * bpf_bprintf_prepare - Generic pass on format strings for bprintf-like helpers
  *
@@ -818,7 +814,7 @@ void bpf_bprintf_cleanup(struct bpf_bprintf_data *data)
  * In argument preparation mode, if 0 is returned, safe temporary buffers are
  * allocated and bpf_bprintf_cleanup should be called to free them after use.
  */
-int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
+int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
 			u32 num_args, struct bpf_bprintf_data *data)
 {
 	bool get_buffers = (data->get_bin_args && num_args) || data->get_buf;
@@ -834,7 +830,7 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
 		return -EINVAL;
 	fmt_size = fmt_end - fmt;
 
-	if (get_buffers && try_get_buffers(&buffers))
+	if (get_buffers && bpf_try_get_buffers(&buffers))
 		return -EBUSY;
 
 	if (data->get_bin_args) {
-- 
2.47.1

[PATCH bpf-next v3 02/12] bpf: Introduce BPF standard streams

[Kumar Kartikeya Dwivedi]

Add support for a stream API to the kernel and expose related kfuncs to
BPF programs. Two streams are exposed, BPF_STDOUT and BPF_STDERR. These
can be used for printing messages that can be consumed from user space,
thus it's similar in spirit to existing trace_pipe interface.

The kernel will use the BPF_STDERR stream to notify the program of any
errors encountered at runtime. BPF programs themselves may use both
streams for writing debug messages. BPF library-like code may use
BPF_STDERR to print warnings or errors on misuse at runtime.

The implementation of a stream is as follows. Everytime a message is
emitted from the kernel (directly, or through a BPF program), a record
is allocated by bump allocating from per-cpu region backed by a page
obtained using try_alloc_pages. This ensures that we can allocate memory
from any context. The eventual plan is to discard this scheme in favor
of Alexei's kmalloc_nolock() [0].

This record is then locklessly inserted into a list (llist_add()) so
that the printing side doesn't require holding any locks, and works in
any context. Each stream has a maximum capacity of 4MB of text, and each
printed message is accounted against this limit.

Messages from a program are emitted using the bpf_stream_vprintk kfunc,
which takes a stream_id argument in addition to working otherwise
similar to bpf_trace_vprintk.

The bprintf buffer helpers are extracted out to be reused for printing
the string into them before copying it into the stream, so that we can
(with the defined max limit) format a string and know its true length
before performing allocations of the stream element.

For consuming elements from a stream, we expose a bpf(2) syscall command
named BPF_PROG_STREAM_READ_BY_FD, which allows reading data from the
stream of a given prog_fd into a user space buffer. The main logic is
implemented in bpf_stream_read(). The log messages are queued in
bpf_stream::log by the bpf_stream_vprintk kfunc, and then pulled and
ordered correctly in the stream backlog.

For this purpose, we hold a lock around bpf_stream_backlog_peek(), as
llist_del_first() (if we maintained a second lockless list for the
backlog) wouldn't be safe from multiple threads anyway. Then, if we
fail to find something in the backlog log, we splice out everything from
the lockless log, and place it in the backlog log, and then return the
head of the backlog. Once the full length of the element is consumed, we
will pop it and free it.

The lockless list bpf_stream::log is a LIFO stack. Elements obtained
using a llist_del_all() operation are in LIFO order, thus would break
the chronological ordering if printed directly. Hence, this batch of
messages is first reversed. Then, it is stashed into a separate list in
the stream, i.e. the backlog_log. The head of this list is the actual
message that should always be returned to the caller. All of this is
done in bpf_stream_backlog_fill().

From the kernel side, the writing into the stream will be a bit more
involved than the typical printk. First, the kernel typically may print
a collection of messages into the stream, and parallel writers into the
stream may suffer from interleaving of messages. To ensure each group of
messages is visible atomically, we can lift the advantage of using a
lockless list for pushing in messages.

To enable this, we add a bpf_stream_stage() macro, and require kernel
users to use bpf_stream_printk statements for the passed expression to
write into the stream. Underneath the macro, we have a message staging
API, where a bpf_stream_stage object on the stack accumulates the
messages being printed into a local llist_head, and then a commit
operation splices the whole batch into the stream's lockless log list.

This is especially pertinent for rqspinlock deadlock messages printed to
program streams. After this change, we see each deadlock invocation as a
non-interleaving contiguous message without any confusion on the
reader's part, improving their user experience in debugging the fault.

While programs cannot benefit from this staged stream writing API, they
could just as well hold an rqspinlock around their print statements to
serialize messages, hence this is kept kernel-internal for now.

Overall, this infrastructure provides NMI-safe any context printing of
messages to two dedicated streams.

Later patches will add support for printing splats in case of BPF arena
page faults, rqspinlock deadlocks, and cond_break timeouts, and
integration of this facility into bpftool for dumping messages to user
space.

Make sure that we don't end up spamming too many errors if the program
keeps failing repeatedly and filling up the stream, hence emit at most
512 error messages from the kernel for a given stream.

  [0]: https://lore.kernel.org/bpf/20250501032718.65476-1-alexei.starovoitov@gmail.com

Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf.h            |  59 ++++
 include/uapi/linux/bpf.h       |  24 ++
 kernel/bpf/Makefile            |   2 +-
 kernel/bpf/core.c              |   5 +
 kernel/bpf/helpers.c           |   1 +
 kernel/bpf/stream.c            | 485 +++++++++++++++++++++++++++++++++
 kernel/bpf/syscall.c           |  27 +-
 tools/include/uapi/linux/bpf.h |  24 ++
 8 files changed, 625 insertions(+), 2 deletions(-)
 create mode 100644 kernel/bpf/stream.c

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4fff0cee8622..cdd726cfe622 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1538,6 +1538,36 @@ struct btf_mod_pair {
 
 struct bpf_kfunc_desc_tab;
 
+enum bpf_stream_id {
+	BPF_STDOUT = 1,
+	BPF_STDERR = 2,
+};
+
+struct bpf_stream_elem {
+	struct llist_node node;
+	int total_len;
+	int consumed_len;
+	char str[];
+};
+
+enum {
+	BPF_STREAM_MAX_CAPACITY = (4 * 1024U * 1024U),
+};
+
+struct bpf_stream {
+	atomic_t capacity;
+	struct llist_head log;	/* list of in-flight stream elements in LIFO order */
+
+	struct mutex lock;  /* lock protecting backlog_{head,tail} */
+	struct llist_node *backlog_head; /* list of in-flight stream elements in FIFO order */
+	struct llist_node *backlog_tail; /* tail of the list above */
+};
+
+struct bpf_stream_stage {
+	struct llist_head log;
+	int len;
+};
+
 struct bpf_prog_aux {
 	atomic64_t refcnt;
 	u32 used_map_cnt;
@@ -1646,6 +1676,8 @@ struct bpf_prog_aux {
 		struct work_struct work;
 		struct rcu_head	rcu;
 	};
+	struct bpf_stream stream[2];
+	atomic_t stream_error_cnt;
 };
 
 struct bpf_prog {
@@ -2408,6 +2440,8 @@ int  generic_map_delete_batch(struct bpf_map *map,
 struct bpf_map *bpf_map_get_curr_or_next(u32 *id);
 struct bpf_prog *bpf_prog_get_curr_or_next(u32 *id);
 
+
+struct page *__bpf_alloc_page(int nid);
 int bpf_map_alloc_pages(const struct bpf_map *map, int nid,
 			unsigned long nr_pages, struct page **page_array);
 #ifdef CONFIG_MEMCG
@@ -3573,6 +3607,31 @@ void bpf_bprintf_cleanup(struct bpf_bprintf_data *data);
 int bpf_try_get_buffers(struct bpf_bprintf_buffers **bufs);
 void bpf_put_buffers(void);
 
+#define BPF_PROG_STREAM_ERROR_CNT 512
+
+void bpf_prog_stream_init(struct bpf_prog *prog);
+void bpf_prog_stream_free(struct bpf_prog *prog);
+int bpf_prog_stream_read(struct bpf_prog *prog, enum bpf_stream_id stream_id, void __user *buf, int len);
+void bpf_stream_stage_init(struct bpf_stream_stage *ss);
+void bpf_stream_stage_free(struct bpf_stream_stage *ss);
+__printf(2, 3)
+int bpf_stream_stage_printk(struct bpf_stream_stage *ss, const char *fmt, ...);
+int bpf_stream_stage_commit(struct bpf_stream_stage *ss, struct bpf_prog *prog,
+			    enum bpf_stream_id stream_id);
+
+bool bpf_prog_stream_error_limit(struct bpf_prog *prog);
+
+#define bpf_stream_printk(ss, ...) bpf_stream_stage_printk(&ss, __VA_ARGS__)
+
+#define bpf_stream_stage(ss, prog, stream_id, expr)                      \
+	({                                                               \
+		if (!bpf_prog_stream_error_limit(prog)) {                \
+			bpf_stream_stage_init(&ss);			 \
+			(expr);                                          \
+			bpf_stream_stage_commit(&ss, prog, stream_id);	 \
+			bpf_stream_stage_free(&ss);			 \
+		}                                                        \
+	})
 
 #ifdef CONFIG_BPF_LSM
 void bpf_cgroup_atype_get(u32 attach_btf_id, int cgroup_atype);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 39e7818cca80..f2fce6a94523 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -906,6 +906,17 @@ union bpf_iter_link_info {
  *		A new file descriptor (a nonnegative integer), or -1 if an
  *		error occurred (in which case, *errno* is set appropriately).
  *
+ * BPF_PROG_STREAM_READ_BY_FD
+ *	Description
+ *		Read data of a program's BPF stream. The program is identified
+ *		by *prog_fd*, and the stream is identified by the *stream_id*.
+ *		The data is copied to a buffer pointed to by *stream_buf*, and
+ *		filled less than or equal to *stream_buf_len* bytes.
+ *
+ *	Return
+ *		Number of bytes read from the stream on success, or -1 if an
+ *		error occurred (in which case, *errno* is set appropriately).
+ *
  * NOTES
  *	eBPF objects (maps and programs) can be shared between processes.
  *
@@ -961,6 +972,7 @@ enum bpf_cmd {
 	BPF_LINK_DETACH,
 	BPF_PROG_BIND_MAP,
 	BPF_TOKEN_CREATE,
+	BPF_PROG_STREAM_READ_BY_FD,
 	__MAX_BPF_CMD,
 };
 
@@ -1463,6 +1475,11 @@ struct bpf_stack_build_id {
 
 #define BPF_OBJ_NAME_LEN 16U
 
+enum {
+	BPF_STREAM_STDOUT = 1,
+	BPF_STREAM_STDERR = 2,
+};
+
 union bpf_attr {
 	struct { /* anonymous struct used by BPF_MAP_CREATE command */
 		__u32	map_type;	/* one of enum bpf_map_type */
@@ -1849,6 +1866,13 @@ union bpf_attr {
 		__u32		bpffs_fd;
 	} token_create;
 
+	struct {
+		__aligned_u64	stream_buf;
+		__u32		stream_buf_len;
+		__u32		stream_id;
+		__u32		prog_fd;
+	} prog_stream_read;
+
 } __attribute__((aligned(8)));
 
 /* The description below is an attempt at providing documentation to eBPF
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 3a335c50e6e3..269c04a24664 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -14,7 +14,7 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
 obj-${CONFIG_BPF_LSM}	  += bpf_inode_storage.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o mprog.o
 obj-$(CONFIG_BPF_JIT) += trampoline.o
-obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o rqspinlock.o
+obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o rqspinlock.o stream.o
 ifeq ($(CONFIG_MMU)$(CONFIG_64BIT),yy)
 obj-$(CONFIG_BPF_SYSCALL) += arena.o range_tree.o
 endif
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index e536a34a32c8..f0def24573ae 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -134,6 +134,10 @@ struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flag
 	mutex_init(&fp->aux->ext_mutex);
 	mutex_init(&fp->aux->dst_mutex);
 
+#ifdef CONFIG_BPF_SYSCALL
+	bpf_prog_stream_init(fp);
+#endif
+
 	return fp;
 }
 
@@ -2862,6 +2866,7 @@ static void bpf_prog_free_deferred(struct work_struct *work)
 	aux = container_of(work, struct bpf_prog_aux, work);
 #ifdef CONFIG_BPF_SYSCALL
 	bpf_free_kfunc_btf_tab(aux->kfunc_btf_tab);
+	bpf_prog_stream_free(aux->prog);
 #endif
 #ifdef CONFIG_CGROUP_BPF
 	if (aux->cgroup_atype != CGROUP_BPF_ATTACH_TYPE_INVALID)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 67d48f9fb173..8fef7b3cbd80 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3393,6 +3393,7 @@ BTF_ID_FLAGS(func, bpf_iter_dmabuf_next, KF_ITER_NEXT | KF_RET_NULL | KF_SLEEPAB
 BTF_ID_FLAGS(func, bpf_iter_dmabuf_destroy, KF_ITER_DESTROY | KF_SLEEPABLE)
 #endif
 BTF_ID_FLAGS(func, __bpf_trap)
+BTF_ID_FLAGS(func, bpf_stream_vprintk, KF_TRUSTED_ARGS)
 BTF_KFUNCS_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {
diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
new file mode 100644
index 000000000000..75ceb6379368
--- /dev/null
+++ b/kernel/bpf/stream.c
@@ -0,0 +1,485 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <linux/bpf.h>
+#include <linux/bpf_mem_alloc.h>
+#include <linux/percpu.h>
+#include <linux/refcount.h>
+#include <linux/gfp.h>
+#include <linux/memory.h>
+#include <linux/local_lock.h>
+#include <linux/mutex.h>
+
+/*
+ * Simple per-CPU NMI-safe bump allocation mechanism, backed by the NMI-safe
+ * try_alloc_pages()/free_pages_nolock() primitives. We allocate a page and
+ * stash it in a local per-CPU variable, and bump allocate from the page
+ * whenever items need to be printed to a stream. Each page holds a global
+ * atomic refcount in its first 4 bytes, and then records of variable length
+ * that describe the printed messages. Once the global refcount has dropped to
+ * zero, it is a signal to free the page back to the kernel's page allocator,
+ * given all the individual records in it have been consumed.
+ *
+ * It is possible the same page is used to serve allocations across different
+ * programs, which may be consumed at different times individually, hence
+ * maintaining a reference count per-page is critical for correct lifetime
+ * tracking.
+ *
+ * The bpf_stream_page code will be replaced to use kmalloc_nolock() once it
+ * lands.
+ */
+struct bpf_stream_page {
+	refcount_t ref;
+	u32 consumed;
+	char buf[];
+};
+
+/* Available room to add data to a refcounted page. */
+#define BPF_STREAM_PAGE_SZ (PAGE_SIZE - offsetofend(struct bpf_stream_page, consumed))
+
+static DEFINE_PER_CPU(local_trylock_t, stream_local_lock) = INIT_LOCAL_TRYLOCK(stream_local_lock);
+static DEFINE_PER_CPU(struct bpf_stream_page *, stream_pcpu_page);
+
+static bool bpf_stream_page_local_lock(unsigned long *flags)
+{
+	return local_trylock_irqsave(&stream_local_lock, *flags);
+}
+
+static void bpf_stream_page_local_unlock(unsigned long *flags)
+{
+	local_unlock_irqrestore(&stream_local_lock, *flags);
+}
+
+static void bpf_stream_page_free(struct bpf_stream_page *stream_page)
+{
+	struct page *p;
+
+	if (!stream_page)
+		return;
+	p = virt_to_page(stream_page);
+	free_pages_nolock(p, 0);
+}
+
+static void bpf_stream_page_get(struct bpf_stream_page *stream_page)
+{
+	refcount_inc(&stream_page->ref);
+}
+
+static void bpf_stream_page_put(struct bpf_stream_page *stream_page)
+{
+	if (refcount_dec_and_test(&stream_page->ref))
+		bpf_stream_page_free(stream_page);
+}
+
+static void bpf_stream_page_init(struct bpf_stream_page *stream_page)
+{
+	refcount_set(&stream_page->ref, 1);
+	stream_page->consumed = 0;
+}
+
+static struct bpf_stream_page *bpf_stream_page_replace(void)
+{
+	struct bpf_stream_page *stream_page, *old_stream_page;
+	struct page *page;
+
+	page = __bpf_alloc_page(NUMA_NO_NODE);
+	if (!page)
+		return NULL;
+	stream_page = page_address(page);
+	bpf_stream_page_init(stream_page);
+
+	old_stream_page = this_cpu_read(stream_pcpu_page);
+	if (old_stream_page)
+		bpf_stream_page_put(old_stream_page);
+	this_cpu_write(stream_pcpu_page, stream_page);
+	return stream_page;
+}
+
+static int bpf_stream_page_check_room(struct bpf_stream_page *stream_page, int len)
+{
+	int min = offsetof(struct bpf_stream_elem, str[0]);
+	int consumed = stream_page->consumed;
+	int total = BPF_STREAM_PAGE_SZ;
+	int rem = max(0, total - consumed - min);
+
+	/* Let's give room of at least 8 bytes. */
+	WARN_ON_ONCE(rem % 8 != 0);
+	rem = rem < 8 ? 0 : rem;
+	return min(len, rem);
+}
+
+static void bpf_stream_elem_init(struct bpf_stream_elem *elem, int len)
+{
+	init_llist_node(&elem->node);
+	elem->total_len = len;
+	elem->consumed_len = 0;
+}
+
+static struct bpf_stream_page *bpf_stream_page_from_elem(struct bpf_stream_elem *elem)
+{
+	unsigned long addr = (unsigned long)elem;
+
+	return (struct bpf_stream_page *)PAGE_ALIGN_DOWN(addr);
+}
+
+static struct bpf_stream_elem *bpf_stream_page_push_elem(struct bpf_stream_page *stream_page, int len)
+{
+	u32 consumed = stream_page->consumed;
+
+	stream_page->consumed += round_up(offsetof(struct bpf_stream_elem, str[len]), 8);
+	return (struct bpf_stream_elem *)&stream_page->buf[consumed];
+}
+
+static noinline struct bpf_stream_elem *bpf_stream_page_reserve_elem(int len)
+{
+	struct bpf_stream_elem *elem = NULL;
+	struct bpf_stream_page *page;
+	int room = 0;
+
+	page = this_cpu_read(stream_pcpu_page);
+	if (!page)
+		page = bpf_stream_page_replace();
+	if (!page)
+		return NULL;
+
+	room = bpf_stream_page_check_room(page, len);
+	if (room != len)
+		page = bpf_stream_page_replace();
+	if (!page)
+		return NULL;
+	bpf_stream_page_get(page);
+	room = bpf_stream_page_check_room(page, len);
+	WARN_ON_ONCE(room != len);
+
+	elem = bpf_stream_page_push_elem(page, room);
+	bpf_stream_elem_init(elem, room);
+	return elem;
+}
+
+static struct bpf_stream_elem *bpf_stream_elem_alloc(int len)
+{
+	const int max_len = ARRAY_SIZE((struct bpf_bprintf_buffers){}.buf);
+	struct bpf_stream_elem *elem;
+	unsigned long flags;
+
+	BUILD_BUG_ON(max_len > BPF_STREAM_PAGE_SZ);
+	/*
+	 * Length denotes the amount of data to be written as part of stream element,
+	 * thus includes '\0' byte. We're capped by how much bpf_bprintf_buffers can
+	 * accomodate, therefore deny allocations that won't fit into them.
+	 */
+	if (len < 0 || len > max_len)
+		return NULL;
+
+	if (!bpf_stream_page_local_lock(&flags))
+		return NULL;
+	elem = bpf_stream_page_reserve_elem(len);
+	bpf_stream_page_local_unlock(&flags);
+	return elem;
+}
+
+static int __bpf_stream_push_str(struct llist_head *log, const char *str, int len)
+{
+	struct bpf_stream_elem *elem = NULL;
+
+	/*
+	 * Allocate a bpf_prog_stream_elem and push it to the bpf_prog_stream
+	 * log, elements will be popped at once and reversed to print the log.
+	 */
+	elem = bpf_stream_elem_alloc(len);
+	if (!elem)
+		return -ENOMEM;
+
+	memcpy(elem->str, str, len);
+	llist_add(&elem->node, log);
+
+	return 0;
+}
+
+static int bpf_stream_consume_capacity(struct bpf_stream *stream, int len)
+{
+	if (atomic_read(&stream->capacity) >= BPF_STREAM_MAX_CAPACITY)
+		return -ENOSPC;
+	if (atomic_add_return(len, &stream->capacity) >= BPF_STREAM_MAX_CAPACITY) {
+		atomic_sub(len, &stream->capacity);
+		return -ENOSPC;
+	}
+	return 0;
+}
+
+static void bpf_stream_release_capacity(struct bpf_stream *stream, struct bpf_stream_elem *elem)
+{
+	int len = elem->total_len;
+
+	atomic_sub(len, &stream->capacity);
+}
+
+static int bpf_stream_push_str(struct bpf_stream *stream, const char *str, int len)
+{
+	int ret = bpf_stream_consume_capacity(stream, len);
+
+	return ret ?: __bpf_stream_push_str(&stream->log, str, len);
+}
+
+static struct bpf_stream *bpf_stream_get(enum bpf_stream_id stream_id, struct bpf_prog_aux *aux)
+{
+	if (stream_id != BPF_STDOUT && stream_id != BPF_STDERR)
+		return NULL;
+	return &aux->stream[stream_id - 1];
+}
+
+static void bpf_stream_free_elem(struct bpf_stream_elem *elem)
+{
+	struct bpf_stream_page *p;
+
+	p = bpf_stream_page_from_elem(elem);
+	bpf_stream_page_put(p);
+}
+
+static void bpf_stream_free_list(struct llist_node *list)
+{
+	struct bpf_stream_elem *elem, *tmp;
+
+	llist_for_each_entry_safe(elem, tmp, list, node)
+		bpf_stream_free_elem(elem);
+}
+
+static struct llist_node *bpf_stream_backlog_peek(struct bpf_stream *stream)
+{
+	return stream->backlog_head;
+}
+
+static struct llist_node *bpf_stream_backlog_pop(struct bpf_stream *stream)
+{
+	struct llist_node *node;
+
+	node = stream->backlog_head;
+	if (stream->backlog_head == stream->backlog_tail)
+		stream->backlog_head = stream->backlog_tail = NULL;
+	else
+		stream->backlog_head = node->next;
+	return node;
+}
+
+static void bpf_stream_backlog_fill(struct bpf_stream *stream)
+{
+	struct llist_node *head, *tail;
+
+	if (llist_empty(&stream->log))
+		return;
+	tail = llist_del_all(&stream->log);
+	if (!tail)
+		return;
+	head = llist_reverse_order(tail);
+
+	if (!stream->backlog_head) {
+		stream->backlog_head = head;
+		stream->backlog_tail = tail;
+	} else {
+		stream->backlog_tail->next = head;
+		stream->backlog_tail = tail;
+	}
+
+	return;
+}
+
+static bool bpf_stream_consume_elem(struct bpf_stream_elem *elem, int *len)
+{
+	int rem = elem->total_len - elem->consumed_len;
+	int used = min(rem, *len);
+
+	elem->consumed_len += used;
+	*len -= used;
+
+	return elem->consumed_len == elem->total_len;
+}
+
+static int bpf_stream_read(struct bpf_stream *stream, void __user *buf, int len)
+{
+	int rem_len = len, cons_len, ret = 0;
+	struct bpf_stream_elem *elem = NULL;
+	struct llist_node *node;
+
+	mutex_lock(&stream->lock);
+
+	while (rem_len) {
+		int pos = len - rem_len;
+		bool cont;
+
+		node = bpf_stream_backlog_peek(stream);
+		if (!node) {
+			bpf_stream_backlog_fill(stream);
+			node = bpf_stream_backlog_peek(stream);
+		}
+		if (!node)
+			break;
+		elem = container_of(node, typeof(*elem), node);
+
+		cons_len = elem->consumed_len;
+		cont = bpf_stream_consume_elem(elem, &rem_len) == false;
+
+		ret = copy_to_user(buf + pos, elem->str + cons_len,
+				   elem->consumed_len - cons_len);
+		/* Restore in case of error. */
+		if (ret) {
+			ret = -EFAULT;
+			elem->consumed_len = cons_len;
+			break;
+		}
+
+		if (cont)
+			continue;
+		bpf_stream_backlog_pop(stream);
+		bpf_stream_release_capacity(stream, elem);
+		bpf_stream_free_elem(elem);
+	}
+
+	mutex_unlock(&stream->lock);
+	return ret ? ret : len - rem_len;
+}
+
+int bpf_prog_stream_read(struct bpf_prog *prog, enum bpf_stream_id stream_id, void __user *buf, int len)
+{
+	struct bpf_stream *stream;
+
+	stream = bpf_stream_get(stream_id, prog->aux);
+	if (!stream)
+		return -ENOENT;
+	return bpf_stream_read(stream, buf, len);
+}
+
+__bpf_kfunc_start_defs();
+
+/*
+ * Avoid using enum bpf_stream_id so that kfunc users don't have to pull in the
+ * enum in headers.
+ */
+__bpf_kfunc int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *args, u32 len__sz, void *aux__prog)
+{
+	struct bpf_bprintf_data data = {
+		.get_bin_args	= true,
+		.get_buf	= true,
+	};
+	struct bpf_prog_aux *aux = aux__prog;
+	u32 fmt_size = strlen(fmt__str) + 1;
+	struct bpf_stream *stream;
+	u32 data_len = len__sz;
+	int ret, num_args;
+
+	stream = bpf_stream_get(stream_id, aux);
+	if (!stream)
+		return -ENOENT;
+
+	if (data_len & 7 || data_len > MAX_BPRINTF_VARARGS * 8 ||
+	    (data_len && !args))
+		return -EINVAL;
+	num_args = data_len / 8;
+
+	ret = bpf_bprintf_prepare(fmt__str, fmt_size, args, num_args, &data);
+	if (ret < 0)
+		return ret;
+
+	ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt__str, data.bin_args);
+	/* If the string was truncated, we only wrote until the size of buffer. */
+	ret = min_t(u32, ret + 1, MAX_BPRINTF_BUF);
+	ret = bpf_stream_push_str(stream, data.buf, ret);
+	bpf_bprintf_cleanup(&data);
+
+	return ret;
+}
+
+__bpf_kfunc_end_defs();
+
+/* Added kfunc to common_btf_ids */
+
+void bpf_prog_stream_init(struct bpf_prog *prog)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(prog->aux->stream); i++) {
+		atomic_set(&prog->aux->stream[i].capacity, 0);
+		init_llist_head(&prog->aux->stream[i].log);
+		mutex_init(&prog->aux->stream[i].lock);
+		prog->aux->stream[i].backlog_head = NULL;
+		prog->aux->stream[i].backlog_tail = NULL;
+	}
+}
+
+void bpf_prog_stream_free(struct bpf_prog *prog)
+{
+	struct llist_node *list;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(prog->aux->stream); i++) {
+		list = llist_del_all(&prog->aux->stream[i].log);
+		bpf_stream_free_list(list);
+		bpf_stream_free_list(prog->aux->stream[i].backlog_head);
+	}
+}
+
+void bpf_stream_stage_init(struct bpf_stream_stage *ss)
+{
+	init_llist_head(&ss->log);
+	ss->len = 0;
+}
+
+void bpf_stream_stage_free(struct bpf_stream_stage *ss)
+{
+	struct llist_node *node;
+
+	node = llist_del_all(&ss->log);
+	bpf_stream_free_list(node);
+}
+
+int bpf_stream_stage_printk(struct bpf_stream_stage *ss, const char *fmt, ...)
+{
+	struct bpf_bprintf_buffers *buf;
+	va_list args;
+	int ret;
+
+	if (bpf_try_get_buffers(&buf))
+		return -EBUSY;
+
+	va_start(args, fmt);
+	ret = vsnprintf(buf->buf, ARRAY_SIZE(buf->buf), fmt, args);
+	va_end(args);
+	/* If the string was truncated, we only wrote until the size of buffer. */
+	ret = min_t(u32, ret + 1, ARRAY_SIZE(buf->buf));
+	ss->len += ret;
+	ret = __bpf_stream_push_str(&ss->log, buf->buf, ret);
+	bpf_put_buffers();
+	return ret;
+}
+
+int bpf_stream_stage_commit(struct bpf_stream_stage *ss, struct bpf_prog *prog,
+			    enum bpf_stream_id stream_id)
+{
+	struct llist_node *list, *head, *tail;
+	struct bpf_stream *stream;
+	int ret;
+
+	stream = bpf_stream_get(stream_id, prog->aux);
+	if (!stream)
+		return -EINVAL;
+
+	ret = bpf_stream_consume_capacity(stream, ss->len);
+	if (ret)
+		return ret;
+
+	list = llist_del_all(&ss->log);
+	head = tail = list;
+
+	if (!list)
+		return 0;
+	while (llist_next(list)) {
+		tail = llist_next(list);
+		list = tail;
+	}
+	llist_add_batch(head, tail, &stream->log);
+	return 0;
+}
+
+bool bpf_prog_stream_error_limit(struct bpf_prog *prog)
+{
+	return atomic_fetch_add(1, &prog->aux->stream_error_cnt) >= BPF_PROG_STREAM_ERROR_CNT;
+}
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 56500381c28a..ac1010b9d11b 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -576,7 +576,7 @@ static bool can_alloc_pages(void)
 		!IS_ENABLED(CONFIG_PREEMPT_RT);
 }
 
-static struct page *__bpf_alloc_page(int nid)
+struct page *__bpf_alloc_page(int nid)
 {
 	if (!can_alloc_pages())
 		return alloc_pages_nolock(nid, 0);
@@ -5936,6 +5936,28 @@ static int token_create(union bpf_attr *attr)
 	return bpf_token_create(attr);
 }
 
+#define BPF_PROG_STREAM_READ_BY_FD_LAST_FIELD prog_stream_read.prog_fd
+
+static int prog_stream_read(union bpf_attr *attr)
+{
+	char __user *buf = u64_to_user_ptr(attr->prog_stream_read.stream_buf);
+	u32 len = attr->prog_stream_read.stream_buf_len;
+	struct bpf_prog *prog;
+	int ret;
+
+	if (CHECK_ATTR(BPF_PROG_STREAM_READ_BY_FD))
+		return -EINVAL;
+
+	prog = bpf_prog_get(attr->prog_stream_read.prog_fd);
+	if (IS_ERR(prog))
+		return PTR_ERR(prog);
+
+	ret = bpf_prog_stream_read(prog, attr->prog_stream_read.stream_id, buf, len);
+	bpf_prog_put(prog);
+
+	return ret;
+}
+
 static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size)
 {
 	union bpf_attr attr;
@@ -6072,6 +6094,9 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size)
 	case BPF_TOKEN_CREATE:
 		err = token_create(&attr);
 		break;
+	case BPF_PROG_STREAM_READ_BY_FD:
+		err = prog_stream_read(&attr);
+		break;
 	default:
 		err = -EINVAL;
 		break;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 39e7818cca80..f2fce6a94523 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -906,6 +906,17 @@ union bpf_iter_link_info {
  *		A new file descriptor (a nonnegative integer), or -1 if an
  *		error occurred (in which case, *errno* is set appropriately).
  *
+ * BPF_PROG_STREAM_READ_BY_FD
+ *	Description
+ *		Read data of a program's BPF stream. The program is identified
+ *		by *prog_fd*, and the stream is identified by the *stream_id*.
+ *		The data is copied to a buffer pointed to by *stream_buf*, and
+ *		filled less than or equal to *stream_buf_len* bytes.
+ *
+ *	Return
+ *		Number of bytes read from the stream on success, or -1 if an
+ *		error occurred (in which case, *errno* is set appropriately).
+ *
  * NOTES
  *	eBPF objects (maps and programs) can be shared between processes.
  *
@@ -961,6 +972,7 @@ enum bpf_cmd {
 	BPF_LINK_DETACH,
 	BPF_PROG_BIND_MAP,
 	BPF_TOKEN_CREATE,
+	BPF_PROG_STREAM_READ_BY_FD,
 	__MAX_BPF_CMD,
 };
 
@@ -1463,6 +1475,11 @@ struct bpf_stack_build_id {
 
 #define BPF_OBJ_NAME_LEN 16U
 
+enum {
+	BPF_STREAM_STDOUT = 1,
+	BPF_STREAM_STDERR = 2,
+};
+
 union bpf_attr {
 	struct { /* anonymous struct used by BPF_MAP_CREATE command */
 		__u32	map_type;	/* one of enum bpf_map_type */
@@ -1849,6 +1866,13 @@ union bpf_attr {
 		__u32		bpffs_fd;
 	} token_create;
 
+	struct {
+		__aligned_u64	stream_buf;
+		__u32		stream_buf_len;
+		__u32		stream_id;
+		__u32		prog_fd;
+	} prog_stream_read;
+
 } __attribute__((aligned(8)));
 
 /* The description below is an attempt at providing documentation to eBPF
-- 
2.47.1

[PATCH bpf-next v3 03/12] bpf: Add function to extract program source info

[Kumar Kartikeya Dwivedi]

Prepare a function for use in future patches that can extract the file
info, line info, and the source line number for a given BPF program
provided it's program counter.

Only the basename of the file path is provided, given it can be
excessively long in some cases.

This will be used in later patches to print source info to the BPF
stream.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf.h |  3 +++
 kernel/bpf/core.c   | 47 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cdd726cfe622..f30697c72ba9 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3667,4 +3667,7 @@ static inline bool bpf_is_subprog(const struct bpf_prog *prog)
 	return prog->aux->func_idx != 0;
 }
 
+int bpf_prog_get_file_line(struct bpf_prog *prog, unsigned long ip, const char **filep,
+			   const char **linep, int *nump);
+
 #endif /* _LINUX_BPF_H */
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index f0def24573ae..5c6e9fbb5508 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -3213,3 +3213,50 @@ EXPORT_SYMBOL(bpf_stats_enabled_key);
 
 EXPORT_TRACEPOINT_SYMBOL_GPL(xdp_exception);
 EXPORT_TRACEPOINT_SYMBOL_GPL(xdp_bulk_tx);
+
+#ifdef CONFIG_BPF_SYSCALL
+
+int bpf_prog_get_file_line(struct bpf_prog *prog, unsigned long ip, const char **filep,
+			   const char **linep, int *nump)
+{
+	int idx = -1, insn_start, insn_end, len;
+	struct bpf_line_info *linfo;
+	void **jited_linfo;
+	struct btf *btf;
+
+	btf = prog->aux->btf;
+	linfo = prog->aux->linfo;
+	jited_linfo = prog->aux->jited_linfo;
+
+	if (!btf || !linfo || !prog->aux->jited_linfo)
+		return -EINVAL;
+	len = prog->aux->func ? prog->aux->func[prog->aux->func_idx]->len : prog->len;
+
+	linfo = &prog->aux->linfo[prog->aux->linfo_idx];
+	jited_linfo = &prog->aux->jited_linfo[prog->aux->linfo_idx];
+
+	insn_start = linfo[0].insn_off;
+	insn_end = insn_start + len;
+
+	for (int i = 0; i < prog->aux->nr_linfo &&
+	     linfo[i].insn_off >= insn_start && linfo[i].insn_off < insn_end; i++) {
+		if (jited_linfo[i] >= (void *)ip)
+			break;
+		idx = i;
+	}
+
+	if (idx == -1)
+		return -ENOENT;
+
+	/* Get base component of the file path. */
+	*filep = btf_name_by_offset(btf, linfo[idx].file_name_off);
+	*filep = kbasename(*filep);
+	/* Obtain the source line, and strip whitespace in prefix. */
+	*linep = btf_name_by_offset(btf, linfo[idx].line_off);
+	while (isspace(**linep))
+		*linep += 1;
+	*nump = BPF_LINE_INFO_LINE_NUM(linfo[idx].line_col);
+	return 0;
+}
+
+#endif
-- 
2.47.1

[PATCH bpf-next v3 04/12] bpf: Ensure RCU lock is held around bpf_prog_ksym_find

[Kumar Kartikeya Dwivedi]

Add a warning to ensure RCU lock is held around tree lookup, and then
fix one of the invocations in bpf_stack_walker. The program has an
active stack frame and won't disappear.

Fixes: f18b03fabaa9 ("bpf: Implement BPF exceptions")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/core.c    | 5 ++++-
 kernel/bpf/helpers.c | 2 ++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 5c6e9fbb5508..b4203f68cf33 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -782,7 +782,10 @@ bool is_bpf_text_address(unsigned long addr)
 
 struct bpf_prog *bpf_prog_ksym_find(unsigned long addr)
 {
-	struct bpf_ksym *ksym = bpf_ksym_find(addr);
+	struct bpf_ksym *ksym;
+
+	WARN_ON_ONCE(!rcu_read_lock_held());
+	ksym = bpf_ksym_find(addr);
 
 	return ksym && ksym->prog ?
 	       container_of(ksym, struct bpf_prog_aux, ksym)->prog :
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 8fef7b3cbd80..61b69eb08c4a 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2936,7 +2936,9 @@ static bool bpf_stack_walker(void *cookie, u64 ip, u64 sp, u64 bp)
 
 	if (!is_bpf_text_address(ip))
 		return !ctx->cnt;
+	rcu_read_lock();
 	prog = bpf_prog_ksym_find(ip);
+	rcu_read_unlock();
 	ctx->cnt++;
 	if (bpf_is_subprog(prog))
 		return true;
-- 
2.47.1

[PATCH bpf-next v3 05/12] bpf: Add function to find program from stack trace

[Kumar Kartikeya Dwivedi]

In preparation of figuring out the closest program that led to the
current point in the kernel, implement a function that scans through the
stack trace and finds out the closest BPF program when walking down the
stack trace.

Special care needs to be taken to skip over kernel and BPF subprog
frames. We basically scan until we find a BPF main prog frame. The
assumption is that if a program calls into us transitively, we'll
hit it along the way. If not, we end up returning NULL.

Contextually the function will be used in places where we know the
program may have called into us.

Due to reliance on arch_bpf_stack_walk(), this function only works on
x86 with CONFIG_UNWINDER_ORC, arm64, and s390. Remove the warning from
arch_bpf_stack_walk as well since we call it outside bpf_throw()
context.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 arch/x86/net/bpf_jit_comp.c |  1 -
 include/linux/bpf.h         |  1 +
 kernel/bpf/core.c           | 28 ++++++++++++++++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 15672cb926fc..40e1b3b9634f 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -3845,7 +3845,6 @@ void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp
 	}
 	return;
 #endif
-	WARN(1, "verification of programs using bpf_throw should have failed\n");
 }
 
 void bpf_arch_poke_desc_update(struct bpf_jit_poke_descriptor *poke,
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f30697c72ba9..cc14ff8e0b88 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3669,5 +3669,6 @@ static inline bool bpf_is_subprog(const struct bpf_prog *prog)
 
 int bpf_prog_get_file_line(struct bpf_prog *prog, unsigned long ip, const char **filep,
 			   const char **linep, int *nump);
+struct bpf_prog *bpf_prog_find_from_stack(void);
 
 #endif /* _LINUX_BPF_H */
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index b4203f68cf33..3871d817396d 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -3262,4 +3262,32 @@ int bpf_prog_get_file_line(struct bpf_prog *prog, unsigned long ip, const char *
 	return 0;
 }
 
+struct walk_stack_ctx {
+	struct bpf_prog *prog;
+};
+
+static bool find_from_stack_cb(void *cookie, u64 ip, u64 sp, u64 bp)
+{
+	struct walk_stack_ctx *ctxp = cookie;
+	struct bpf_prog *prog;
+
+	rcu_read_lock();
+	prog = bpf_prog_ksym_find(ip);
+	rcu_read_unlock();
+	if (!prog)
+		return true;
+	if (bpf_is_subprog(prog))
+		return true;
+	ctxp->prog = prog;
+	return false;
+}
+
+struct bpf_prog *bpf_prog_find_from_stack(void)
+{
+	struct walk_stack_ctx ctx = {};
+
+	arch_bpf_stack_walk(find_from_stack_cb, &ctx);
+	return ctx.prog;
+}
+
 #endif
-- 
2.47.1

[PATCH bpf-next v3 06/12] bpf: Add dump_stack() analogue to print to BPF stderr

[Kumar Kartikeya Dwivedi]

Introduce a kernel function which is the analogue of dump_stack()
printing some useful information and the stack trace. This is not
exposed to BPF programs yet, but can be made available in the future.

When we have a program counter for a BPF program in the stack trace,
also additionally output the filename and line number to make the trace
helpful. The rest of the trace can be passed into ./decode_stacktrace.sh
to obtain the line numbers for kernel symbols.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf.h |  2 ++
 kernel/bpf/stream.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cc14ff8e0b88..bd3cde41795e 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3618,10 +3618,12 @@ __printf(2, 3)
 int bpf_stream_stage_printk(struct bpf_stream_stage *ss, const char *fmt, ...);
 int bpf_stream_stage_commit(struct bpf_stream_stage *ss, struct bpf_prog *prog,
 			    enum bpf_stream_id stream_id);
+int bpf_stream_stage_dump_stack(struct bpf_stream_stage *ss);
 
 bool bpf_prog_stream_error_limit(struct bpf_prog *prog);
 
 #define bpf_stream_printk(ss, ...) bpf_stream_stage_printk(&ss, __VA_ARGS__)
+#define bpf_stream_dump_stack(ss) bpf_stream_stage_dump_stack(&ss)
 
 #define bpf_stream_stage(ss, prog, stream_id, expr)                      \
 	({                                                               \
diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
index 75ceb6379368..5fb11202ab9c 100644
--- a/kernel/bpf/stream.c
+++ b/kernel/bpf/stream.c
@@ -2,6 +2,7 @@
 /* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
 
 #include <linux/bpf.h>
+#include <linux/filter.h>
 #include <linux/bpf_mem_alloc.h>
 #include <linux/percpu.h>
 #include <linux/refcount.h>
@@ -483,3 +484,46 @@ bool bpf_prog_stream_error_limit(struct bpf_prog *prog)
 {
 	return atomic_fetch_add(1, &prog->aux->stream_error_cnt) >= BPF_PROG_STREAM_ERROR_CNT;
 }
+
+struct dump_stack_ctx {
+	struct bpf_stream_stage *ss;
+	int err;
+};
+
+static bool dump_stack_cb(void *cookie, u64 ip, u64 sp, u64 bp)
+{
+	struct dump_stack_ctx *ctxp = cookie;
+	const char *file = "", *line = "";
+	struct bpf_prog *prog;
+	int num, ret;
+
+	if (is_bpf_text_address(ip)) {
+		rcu_read_lock();
+		prog = bpf_prog_ksym_find(ip);
+		rcu_read_unlock();
+		ret = bpf_prog_get_file_line(prog, ip, &file, &line, &num);
+		if (ret < 0)
+			goto end;
+		ctxp->err = bpf_stream_stage_printk(ctxp->ss, "%pS\n  %s @ %s:%d\n",
+						    (void *)ip, line, file, num);
+		return !ctxp->err;
+	}
+end:
+	ctxp->err = bpf_stream_stage_printk(ctxp->ss, "%pS\n", (void *)ip);
+	return !ctxp->err;
+}
+
+int bpf_stream_stage_dump_stack(struct bpf_stream_stage *ss)
+{
+	struct dump_stack_ctx ctx = { .ss = ss };
+	int ret;
+
+	ret = bpf_stream_stage_printk(ss, "CPU: %d UID: %d PID: %d Comm: %s\n",
+				      raw_smp_processor_id(), __kuid_val(current_real_cred()->euid),
+				      current->pid, current->comm);
+	ret = ret ?: bpf_stream_stage_printk(ss, "Call trace:\n");
+	if (!ret)
+		arch_bpf_stack_walk(dump_stack_cb, &ctx);
+	ret = ret ?: ctx.err;
+	return ret ?: bpf_stream_stage_printk(ss, "\n");
+}
-- 
2.47.1

[PATCH bpf-next v3 07/12] bpf: Report may_goto timeout to BPF stderr

[Kumar Kartikeya Dwivedi]

Begin reporting may_goto timeouts to BPF program's stderr stream.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/core.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 3871d817396d..7ff2d37625f5 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -3168,6 +3168,22 @@ u64 __weak arch_bpf_timed_may_goto(void)
 	return 0;
 }
 
+static noinline void bpf_prog_report_may_goto_violation(void)
+{
+#ifdef CONFIG_BPF_SYSCALL
+	struct bpf_stream_stage ss;
+	struct bpf_prog *prog;
+
+	prog = bpf_prog_find_from_stack();
+	if (!prog)
+		return;
+	bpf_stream_stage(ss, prog, BPF_STDERR, ({
+		bpf_stream_printk(ss, "ERROR: Timeout detected for may_goto instruction\n");
+		bpf_stream_dump_stack(ss);
+	}));
+#endif
+}
+
 u64 bpf_check_timed_may_goto(struct bpf_timed_may_goto *p)
 {
 	u64 time = ktime_get_mono_fast_ns();
@@ -3178,8 +3194,10 @@ u64 bpf_check_timed_may_goto(struct bpf_timed_may_goto *p)
 		return BPF_MAX_TIMED_LOOPS;
 	}
 	/* Check if we've exhausted our time slice, and zero count. */
-	if (time - p->timestamp >= (NSEC_PER_SEC / 4))
+	if (unlikely(time - p->timestamp >= (NSEC_PER_SEC / 4))) {
+		bpf_prog_report_may_goto_violation();
 		return 0;
+	}
 	/* Refresh the count for the stack frame. */
 	return BPF_MAX_TIMED_LOOPS;
 }
-- 
2.47.1

[PATCH bpf-next v3 08/12] bpf: Report rqspinlock deadlocks/timeout to BPF stderr

[Kumar Kartikeya Dwivedi]

Begin reporting rqspinlock deadlocks and timeout to BPF program's
stderr.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/rqspinlock.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index 338305c8852c..5ab354d55d82 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -666,6 +666,27 @@ EXPORT_SYMBOL_GPL(resilient_queued_spin_lock_slowpath);
 
 __bpf_kfunc_start_defs();
 
+static void bpf_prog_report_rqspinlock_violation(const char *str, void *lock, bool irqsave)
+{
+	struct rqspinlock_held *rqh = this_cpu_ptr(&rqspinlock_held_locks);
+	struct bpf_stream_stage ss;
+	struct bpf_prog *prog;
+
+	prog = bpf_prog_find_from_stack();
+	if (!prog)
+		return;
+	bpf_stream_stage(ss, prog, BPF_STDERR, ({
+		bpf_stream_printk(ss, "ERROR: %s for bpf_res_spin_lock%s\n", str, irqsave ? "_irqsave" : "");
+		bpf_stream_printk(ss, "Attempted lock   = 0x%px\n", lock);
+		bpf_stream_printk(ss, "Total held locks = %d\n", rqh->cnt);
+		for (int i = 0; i < min(RES_NR_HELD, rqh->cnt); i++)
+			bpf_stream_printk(ss, "Held lock[%2d] = 0x%px\n", i, rqh->locks[i]);
+		bpf_stream_dump_stack(ss);
+	}));
+}
+
+#define REPORT_STR(ret) ({ (ret) == -ETIMEDOUT ? "Timeout detected" : "AA or ABBA deadlock detected"; })
+
 __bpf_kfunc int bpf_res_spin_lock(struct bpf_res_spin_lock *lock)
 {
 	int ret;
@@ -676,6 +697,7 @@ __bpf_kfunc int bpf_res_spin_lock(struct bpf_res_spin_lock *lock)
 	preempt_disable();
 	ret = res_spin_lock((rqspinlock_t *)lock);
 	if (unlikely(ret)) {
+		bpf_prog_report_rqspinlock_violation(REPORT_STR(ret), lock, false);
 		preempt_enable();
 		return ret;
 	}
@@ -698,6 +720,7 @@ __bpf_kfunc int bpf_res_spin_lock_irqsave(struct bpf_res_spin_lock *lock, unsign
 	local_irq_save(flags);
 	ret = res_spin_lock((rqspinlock_t *)lock);
 	if (unlikely(ret)) {
+		bpf_prog_report_rqspinlock_violation(REPORT_STR(ret), lock, true);
 		local_irq_restore(flags);
 		preempt_enable();
 		return ret;
-- 
2.47.1

[PATCH bpf-next v3 09/12] libbpf: Add bpf_stream_printk() macro

[Kumar Kartikeya Dwivedi]

Add a convenience macro to print data to the BPF streams. BPF_STDOUT and
BPF_STDERR stream IDs in the vmlinux.h can be passed to the macro to
print to the respective streams.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 tools/lib/bpf/bpf_helpers.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index a50773d4616e..76b127a9f24d 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -314,6 +314,22 @@ enum libbpf_tristate {
 			  ___param, sizeof(___param));		\
 })
 
+extern int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *args,
+			      __u32 len__sz, void *aux__prog) __weak __ksym;
+
+#define bpf_stream_printk(stream_id, fmt, args...)				\
+({										\
+	static const char ___fmt[] = fmt;					\
+	unsigned long long ___param[___bpf_narg(args)];				\
+										\
+	_Pragma("GCC diagnostic push")						\
+	_Pragma("GCC diagnostic ignored \"-Wint-conversion\"")			\
+	___bpf_fill(___param, args);						\
+	_Pragma("GCC diagnostic pop")						\
+										\
+	bpf_stream_vprintk(stream_id, ___fmt, ___param, sizeof(___param), NULL);\
+})
+
 /* Use __bpf_printk when bpf_printk call has 3 or fewer fmt args
  * Otherwise use __bpf_vprintk
  */
-- 
2.47.1

[PATCH bpf-next v3 10/12] libbpf: Introduce bpf_prog_stream_read() API

[Kumar Kartikeya Dwivedi]

Introduce a libbpf API so that users can read data from a given BPF
stream for a BPF prog fd. For now, only the low-level syscall wrapper
is provided, we can add a bpf_program__* accessor as a follow up if
needed.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 tools/lib/bpf/bpf.c      | 20 ++++++++++++++++++++
 tools/lib/bpf/bpf.h      | 21 +++++++++++++++++++++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 42 insertions(+)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 6eb421ccf91b..ab40dbf9f020 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -1375,3 +1375,23 @@ int bpf_token_create(int bpffs_fd, struct bpf_token_create_opts *opts)
 	fd = sys_bpf_fd(BPF_TOKEN_CREATE, &attr, attr_sz);
 	return libbpf_err_errno(fd);
 }
+
+int bpf_prog_stream_read(int prog_fd, __u32 stream_id, void *buf, __u32 buf_len,
+			 struct bpf_prog_stream_read_opts *opts)
+{
+	const size_t attr_sz = offsetofend(union bpf_attr, prog_stream_read);
+	union bpf_attr attr;
+	int err;
+
+	if (!OPTS_VALID(opts, bpf_prog_stream_read_opts))
+		return libbpf_err(-EINVAL);
+
+	memset(&attr, 0, attr_sz);
+	attr.prog_stream_read.stream_buf = ptr_to_u64(buf);
+	attr.prog_stream_read.stream_buf_len = buf_len;
+	attr.prog_stream_read.stream_id = stream_id;
+	attr.prog_stream_read.prog_fd = prog_fd;
+
+	err = sys_bpf(BPF_PROG_STREAM_READ_BY_FD, &attr, attr_sz);
+	return libbpf_err_errno(err);
+}
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 1342564214c8..7252150e7ad3 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -709,6 +709,27 @@ struct bpf_token_create_opts {
 LIBBPF_API int bpf_token_create(int bpffs_fd,
 				struct bpf_token_create_opts *opts);
 
+struct bpf_prog_stream_read_opts {
+	size_t sz;
+	size_t :0;
+};
+#define bpf_prog_stream_read_opts__last_field sz
+/**
+ * @brief **bpf_prog_stream_read** reads data from the BPF stream of a given BPF
+ * program.
+ *
+ * @param prog_fd FD for the BPF program whose BPF stream is to be read.
+ * @param stream_id ID of the BPF stream to be read.
+ * @param buf Buffer to read data into from the BPF stream.
+ * @param buf_len Maximum number of bytes to read from the BPF stream.
+ * @param opts optional options, can be NULL
+ *
+ * @return The number of bytes read, on success; negative error code, otherwise
+ * (errno is also set to the error code)
+ */
+LIBBPF_API int bpf_prog_stream_read(int prog_fd, __u32 stream_id, void *buf, __u32 buf_len,
+				    struct bpf_prog_stream_read_opts *opts);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index c7fc0bde5648..1bbf77326420 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -437,6 +437,7 @@ LIBBPF_1.6.0 {
 		bpf_linker__add_fd;
 		bpf_linker__new_fd;
 		bpf_object__prepare;
+		bpf_prog_stream_read;
 		bpf_program__attach_cgroup_opts;
 		bpf_program__func_info;
 		bpf_program__func_info_cnt;
-- 
2.47.1

[PATCH bpf-next v3 11/12] bpftool: Add support for dumping streams

[Kumar Kartikeya Dwivedi]

Add support for printing the BPF stream contents of a program in
bpftool. The new bpftool prog tracelog command is extended to take
stdout and stderr arguments, and then the prog specification.

The bpf_prog_stream_read() API added in previous patch is simply reused
to grab data and then it is dumped to the respective file. The stdout
data is sent to stdout, and stderr is printed to stderr.

Cc: Quentin Monnet <qmo@kernel.org>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../bpftool/Documentation/bpftool-prog.rst    |  7 +++
 tools/bpf/bpftool/bash-completion/bpftool     | 16 +++++-
 tools/bpf/bpftool/prog.c                      | 49 ++++++++++++++++++-
 3 files changed, 70 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
index da3152c16228..f69fd92df8d8 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
@@ -35,6 +35,7 @@ PROG COMMANDS
 | **bpftool** **prog attach** *PROG* *ATTACH_TYPE* [*MAP*]
 | **bpftool** **prog detach** *PROG* *ATTACH_TYPE* [*MAP*]
 | **bpftool** **prog tracelog**
+| **bpftool** **prog tracelog** [ { **stdout** | **stderr**  } *PROG* ]
 | **bpftool** **prog run** *PROG* **data_in** *FILE* [**data_out** *FILE* [**data_size_out** *L*]] [**ctx_in** *FILE* [**ctx_out** *FILE* [**ctx_size_out** *M*]]] [**repeat** *N*]
 | **bpftool** **prog profile** *PROG* [**duration** *DURATION*] *METRICs*
 | **bpftool** **prog help**
@@ -179,6 +180,12 @@ bpftool prog tracelog
     purposes. For streaming data from BPF programs to user space, one can use
     perf events (see also **bpftool-map**\ (8)).
 
+bpftool prog tracelog { stdout | stderr } *PROG*
+    Dump the BPF stream of the program. BPF programs can write to these streams
+    at runtime with the **bpf_stream_vprintk**\ () kfunc. The kernel may write
+    error messages to the standard error stream. This facility should be used
+    only for debugging purposes.
+
 bpftool prog run *PROG* data_in *FILE* [data_out *FILE* [data_size_out *L*]] [ctx_in *FILE* [ctx_out *FILE* [ctx_size_out *M*]]] [repeat *N*]
     Run BPF program *PROG* in the kernel testing infrastructure for BPF,
     meaning that the program works on the data and context provided by the
diff --git a/tools/bpf/bpftool/bash-completion/bpftool b/tools/bpf/bpftool/bash-completion/bpftool
index 27512feb5c70..a759ba24471d 100644
--- a/tools/bpf/bpftool/bash-completion/bpftool
+++ b/tools/bpf/bpftool/bash-completion/bpftool
@@ -518,7 +518,21 @@ _bpftool()
                     esac
                     ;;
                 tracelog)
-                    return 0
+                    case $prev in
+                        $command)
+                            COMPREPLY+=( $( compgen -W "stdout stderr" -- \
+                                "$cur" ) )
+                            return 0
+                            ;;
+                        stdout|stderr)
+                            COMPREPLY=( $( compgen -W "$PROG_TYPE" -- \
+                                "$cur" ) )
+                            return 0
+                            ;;
+                        *)
+                            return 0
+                            ;;
+                    esac
                     ;;
                 profile)
                     case $cword in
diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index deeaa5c1ed7d..9722d841abc0 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -1113,6 +1113,52 @@ static int do_detach(int argc, char **argv)
 	return 0;
 }
 
+enum prog_tracelog_mode {
+	TRACE_STDOUT,
+	TRACE_STDERR,
+};
+
+static int
+prog_tracelog_stream(int prog_fd, enum prog_tracelog_mode mode)
+{
+	FILE *file = mode == TRACE_STDOUT ? stdout : stderr;
+	int stream_id = mode == TRACE_STDOUT ? 1 : 2;
+	char buf[512];
+	int ret;
+
+	ret = 0;
+	do {
+		ret = bpf_prog_stream_read(prog_fd, stream_id, buf, sizeof(buf), NULL);
+		if (ret > 0)
+			fwrite(buf, sizeof(buf[0]), ret, file);
+	} while (ret > 0);
+
+	fflush(file);
+	return ret ? -1 : 0;
+}
+
+static int do_tracelog_any(int argc, char **argv)
+{
+	enum prog_tracelog_mode mode;
+	int fd;
+
+	if (argc == 0)
+		return do_tracelog(argc, argv);
+	if (!is_prefix(*argv, "stdout") && !is_prefix(*argv, "stderr"))
+		usage();
+	mode = is_prefix(*argv, "stdout") ? TRACE_STDOUT : TRACE_STDERR;
+	NEXT_ARG();
+
+	if (!REQ_ARGS(2))
+		return -1;
+
+	fd = prog_parse_fd(&argc, &argv);
+	if (fd < 0)
+		return -1;
+
+	return prog_tracelog_stream(fd, mode);
+}
+
 static int check_single_stdin(char *file_data_in, char *file_ctx_in)
 {
 	if (file_data_in && file_ctx_in &&
@@ -2493,6 +2539,7 @@ static int do_help(int argc, char **argv)
 		"                         [repeat N]\n"
 		"       %1$s %2$s profile PROG [duration DURATION] METRICs\n"
 		"       %1$s %2$s tracelog\n"
+		"       %1$s %2$s tracelog { stdout | stderr } PROG\n"
 		"       %1$s %2$s help\n"
 		"\n"
 		"       " HELP_SPEC_MAP "\n"
@@ -2532,7 +2579,7 @@ static const struct cmd cmds[] = {
 	{ "loadall",	do_loadall },
 	{ "attach",	do_attach },
 	{ "detach",	do_detach },
-	{ "tracelog",	do_tracelog },
+	{ "tracelog",	do_tracelog_any },
 	{ "run",	do_run },
 	{ "profile",	do_profile },
 	{ 0 }
-- 
2.47.1

[PATCH bpf-next v3 12/12] selftests/bpf: Add tests for prog streams

[Kumar Kartikeya Dwivedi]

Add selftests to stress test the various facets of the stream API,
memory allocation pattern, and ensuring dumping support is tested and
functional.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../testing/selftests/bpf/prog_tests/stream.c | 140 ++++++++++++++++++
 tools/testing/selftests/bpf/progs/stream.c    |  75 ++++++++++
 .../testing/selftests/bpf/progs/stream_fail.c |  17 +++
 3 files changed, 232 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/stream.c
 create mode 100644 tools/testing/selftests/bpf/progs/stream.c
 create mode 100644 tools/testing/selftests/bpf/progs/stream_fail.c

diff --git a/tools/testing/selftests/bpf/prog_tests/stream.c b/tools/testing/selftests/bpf/prog_tests/stream.c
new file mode 100644
index 000000000000..b14ce6e682aa
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/stream.c
@@ -0,0 +1,140 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include <sys/mman.h>
+#include <regex.h>
+
+#include "stream.skel.h"
+#include "stream_fail.skel.h"
+
+void test_stream_failure(void)
+{
+	RUN_TESTS(stream_fail);
+}
+
+void test_stream_success(void)
+{
+	RUN_TESTS(stream);
+	return;
+}
+
+struct {
+	int prog_off;
+	const char *errstr;
+} stream_error_arr[] = {
+	{
+		offsetof(struct stream, progs.stream_cond_break),
+		"ERROR: Timeout detected for may_goto instruction\n\0"
+		"CPU: [0-9]+ UID: 0 PID: [0-9]+ Comm: test_progs\n\0"
+		"Call trace:\n\0"
+		"([a-zA-Z_][a-zA-Z0-9_]*\\+0x[0-9a-fA-F]+/0x[0-9a-fA-F]+\n\0"
+		"|[ \t]+[^\n]+\n\0)*",
+	},
+	{
+		offsetof(struct stream, progs.stream_deadlock),
+		"ERROR: AA or ABBA deadlock detected for bpf_res_spin_lock\n\0"
+		"Attempted lock   = (0x[0-9a-fA-F]+)\n\0"
+		"Total held locks = 1\n\0"
+		"Held lock\\[ 0\\] = \\1\n\0"  // Lock address must match
+		"CPU: [0-9]+ UID: 0 PID: [0-9]+ Comm: test_progs\n\0"
+		"Call trace:\n\0"
+		"([a-zA-Z_][a-zA-Z0-9_]*\\+0x[0-9a-fA-F]+/0x[0-9a-fA-F]+\n\0"
+		"|[ \t]+[^\n]+\n\0)*",
+	},
+};
+
+static int match_regex(const char *pattern, const char *string)
+{
+	int err, rc;
+	regex_t re;
+
+	err = regcomp(&re, pattern, REG_EXTENDED | REG_NEWLINE);
+	if (err)
+		return -1;
+	rc = regexec(&re, string, 0, NULL, 0);
+	regfree(&re);
+	return rc == 0 ? 1 : 0;
+}
+
+void test_stream_errors(void)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, opts);
+	LIBBPF_OPTS(bpf_prog_stream_read_opts, ropts);
+	char buf[1024] = {};
+	struct stream *skel;
+	int ret, prog_fd;
+
+	skel = stream__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "stream__open_and_load"))
+		return;
+
+	for (int i = 0; i < ARRAY_SIZE(stream_error_arr); i++) {
+		struct bpf_program **prog;
+
+		prog = (struct bpf_program **)(((char *)skel) + stream_error_arr[i].prog_off);
+		prog_fd = bpf_program__fd(*prog);
+		ret = bpf_prog_test_run_opts(prog_fd, &opts);
+		ASSERT_OK(ret, "ret");
+		ASSERT_OK(opts.retval, "retval");
+
+#if !defined(__x86_64__)
+		ASSERT_TRUE(1, "Timed may_goto unsupported, skip.");
+		if (i == 0) {
+			ret = bpf_prog_stream_read(prog_fd, 2, buf, sizeof(buf), &ropts);
+			ASSERT_EQ(ret, 0, "stream read");
+			continue;
+		}
+#endif
+
+		ret = bpf_prog_stream_read(prog_fd, BPF_STREAM_STDERR, buf, sizeof(buf), &ropts);
+		ASSERT_GT(ret, 0, "stream read");
+		ASSERT_LE(ret, 1023, "len for buf");
+		buf[ret] = '\0';
+
+		ret = match_regex(stream_error_arr[i].errstr, buf);
+		ASSERT_TRUE(ret == 1, "regex match");
+	}
+
+	stream__destroy(skel);
+}
+
+void test_stream_syscall(void)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, opts);
+	LIBBPF_OPTS(bpf_prog_stream_read_opts, ropts);
+	struct stream *skel;
+	int ret, prog_fd;
+	char buf[64];
+
+	skel = stream__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "stream__open_and_load"))
+		return;
+
+	prog_fd = bpf_program__fd(skel->progs.stream_syscall);
+	ret = bpf_prog_test_run_opts(prog_fd, &opts);
+	ASSERT_OK(ret, "ret");
+	ASSERT_OK(opts.retval, "retval");
+
+	ASSERT_LT(bpf_prog_stream_read(0, BPF_STREAM_STDOUT, buf, sizeof(buf), &ropts), 0, "error");
+	ret = -errno;
+	ASSERT_EQ(ret, -EINVAL, "bad prog_fd");
+
+	ASSERT_LT(bpf_prog_stream_read(prog_fd, 0, buf, sizeof(buf), &ropts), 0, "error");
+	ret = -errno;
+	ASSERT_EQ(ret, -ENOENT, "bad stream id");
+
+	ASSERT_LT(bpf_prog_stream_read(prog_fd, BPF_STREAM_STDOUT, NULL, sizeof(buf), NULL), 0, "error");
+	ret = -errno;
+	ASSERT_EQ(ret, -EFAULT, "bad stream buf");
+
+	ret = bpf_prog_stream_read(prog_fd, BPF_STREAM_STDOUT, buf, 2, NULL);
+	ASSERT_EQ(ret, 2, "bytes");
+	ret = bpf_prog_stream_read(prog_fd, BPF_STREAM_STDOUT, buf, 2, NULL);
+	ASSERT_EQ(ret, 2, "bytes");
+	ret = bpf_prog_stream_read(prog_fd, BPF_STREAM_STDOUT, buf, 1, &ropts);
+	ASSERT_EQ(ret, 0, "no bytes stdout");
+	ret = bpf_prog_stream_read(prog_fd, BPF_STREAM_STDERR, buf, 1, &ropts);
+	ASSERT_EQ(ret, 0, "no bytes stderr");
+
+	stream__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/stream.c b/tools/testing/selftests/bpf/progs/stream.c
new file mode 100644
index 000000000000..1fb0e810afc6
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/stream.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+#include "bpf_experimental.h"
+
+struct arr_elem {
+	struct bpf_res_spin_lock lock;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct arr_elem);
+} arrmap SEC(".maps");
+
+#define ENOSPC 28
+#define _STR "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+
+#define STREAM_STR (u64)(_STR _STR _STR _STR)
+
+SEC("syscall")
+__success __retval(0)
+int stream_exhaust(void *ctx)
+{
+	bpf_repeat(BPF_MAX_LOOPS)
+		if (bpf_stream_printk(BPF_STDOUT, _STR) == -ENOSPC)
+			return 0;
+	return 1;
+}
+
+SEC("syscall")
+__success __retval(0)
+int stream_cond_break(void *ctx)
+{
+	while (can_loop)
+		;
+	return 0;
+}
+
+SEC("syscall")
+__success __retval(0)
+int stream_deadlock(void *ctx)
+{
+	struct bpf_res_spin_lock *lock, *nlock;
+
+	lock = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!lock)
+		return 0;
+	nlock = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!nlock)
+		return 0;
+	if (bpf_res_spin_lock(lock))
+		return 0;
+	if (bpf_res_spin_lock(nlock)) {
+		bpf_res_spin_unlock(lock);
+		return 0;
+	}
+	bpf_res_spin_unlock(nlock);
+	bpf_res_spin_unlock(lock);
+	return 0;
+}
+
+SEC("syscall")
+__success __retval(0)
+int stream_syscall(void *ctx)
+{
+	bpf_stream_printk(BPF_STDOUT, "foo");
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/stream_fail.c b/tools/testing/selftests/bpf/progs/stream_fail.c
new file mode 100644
index 000000000000..12004d5092b7
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/stream_fail.c
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+#include "bpf_misc.h"
+
+SEC("syscall")
+__failure __msg("Possibly NULL pointer passed")
+int stream_vprintk_null_arg(void *ctx)
+{
+	bpf_stream_vprintk(BPF_STDOUT, "", NULL, 0, NULL);
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.47.1

Re: [PATCH bpf-next v3 06/12] bpf: Add dump_stack() analogue to print to BPF stderr

[Jiri Olsa]

On Mon, Jun 23, 2025 at 08:12:46PM -0700, Kumar Kartikeya Dwivedi wrote:

SNIP

> diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
> index 75ceb6379368..5fb11202ab9c 100644
> --- a/kernel/bpf/stream.c
> +++ b/kernel/bpf/stream.c
> @@ -2,6 +2,7 @@
>  /* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
>  
>  #include <linux/bpf.h>
> +#include <linux/filter.h>
>  #include <linux/bpf_mem_alloc.h>
>  #include <linux/percpu.h>
>  #include <linux/refcount.h>
> @@ -483,3 +484,46 @@ bool bpf_prog_stream_error_limit(struct bpf_prog *prog)
>  {
>  	return atomic_fetch_add(1, &prog->aux->stream_error_cnt) >= BPF_PROG_STREAM_ERROR_CNT;
>  }
> +
> +struct dump_stack_ctx {
> +	struct bpf_stream_stage *ss;
> +	int err;
> +};
> +
> +static bool dump_stack_cb(void *cookie, u64 ip, u64 sp, u64 bp)
> +{
> +	struct dump_stack_ctx *ctxp = cookie;
> +	const char *file = "", *line = "";
> +	struct bpf_prog *prog;
> +	int num, ret;
> +
> +	if (is_bpf_text_address(ip)) {
> +		rcu_read_lock();
> +		prog = bpf_prog_ksym_find(ip);
> +		rcu_read_unlock();

do you need to check prog != NULL ?

also is_bpf_text_address calls bpf_ksym_find and bpf_prog_ksym_find calls it again,
I think it'd be better just to call bpf_prog_ksym_find from here

jirka


> +		ret = bpf_prog_get_file_line(prog, ip, &file, &line, &num);
> +		if (ret < 0)
> +			goto end;
> +		ctxp->err = bpf_stream_stage_printk(ctxp->ss, "%pS\n  %s @ %s:%d\n",
> +						    (void *)ip, line, file, num);
> +		return !ctxp->err;
> +	}
> +end:
> +	ctxp->err = bpf_stream_stage_printk(ctxp->ss, "%pS\n", (void *)ip);
> +	return !ctxp->err;
> +}
> +
> +int bpf_stream_stage_dump_stack(struct bpf_stream_stage *ss)
> +{
> +	struct dump_stack_ctx ctx = { .ss = ss };
> +	int ret;
> +
> +	ret = bpf_stream_stage_printk(ss, "CPU: %d UID: %d PID: %d Comm: %s\n",
> +				      raw_smp_processor_id(), __kuid_val(current_real_cred()->euid),
> +				      current->pid, current->comm);
> +	ret = ret ?: bpf_stream_stage_printk(ss, "Call trace:\n");
> +	if (!ret)
> +		arch_bpf_stack_walk(dump_stack_cb, &ctx);
> +	ret = ret ?: ctx.err;
> +	return ret ?: bpf_stream_stage_printk(ss, "\n");
> +}
> -- 
> 2.47.1
> 
> 

Re: [PATCH bpf-next v3 06/12] bpf: Add dump_stack() analogue to print to BPF stderr

[Kumar Kartikeya Dwivedi]

On Tue, 24 Jun 2025 at 13:38, Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Mon, Jun 23, 2025 at 08:12:46PM -0700, Kumar Kartikeya Dwivedi wrote:
>
> SNIP
>
> > diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
> > index 75ceb6379368..5fb11202ab9c 100644
> > --- a/kernel/bpf/stream.c
> > +++ b/kernel/bpf/stream.c
> > @@ -2,6 +2,7 @@
> >  /* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
> >
> >  #include <linux/bpf.h>
> > +#include <linux/filter.h>
> >  #include <linux/bpf_mem_alloc.h>
> >  #include <linux/percpu.h>
> >  #include <linux/refcount.h>
> > @@ -483,3 +484,46 @@ bool bpf_prog_stream_error_limit(struct bpf_prog *prog)
> >  {
> >       return atomic_fetch_add(1, &prog->aux->stream_error_cnt) >= BPF_PROG_STREAM_ERROR_CNT;
> >  }
> > +
> > +struct dump_stack_ctx {
> > +     struct bpf_stream_stage *ss;
> > +     int err;
> > +};
> > +
> > +static bool dump_stack_cb(void *cookie, u64 ip, u64 sp, u64 bp)
> > +{
> > +     struct dump_stack_ctx *ctxp = cookie;
> > +     const char *file = "", *line = "";
> > +     struct bpf_prog *prog;
> > +     int num, ret;
> > +
> > +     if (is_bpf_text_address(ip)) {
> > +             rcu_read_lock();
> > +             prog = bpf_prog_ksym_find(ip);
> > +             rcu_read_unlock();
>
> do you need to check prog != NULL ?

I think it should be non-NULL, given we're walking IPs of progs with
an active stack frame so they're not going away.

>
> also is_bpf_text_address calls bpf_ksym_find and bpf_prog_ksym_find calls it again,
> I think it'd be better just to call bpf_prog_ksym_find from here
>

Good point, I will fix that. Then just check it for NULL once and
continue using it.

Thanks!

> jirka
>
>
> > +             ret = bpf_prog_get_file_line(prog, ip, &file, &line, &num);
> > +             if (ret < 0)
> > +                     goto end;
> > +             ctxp->err = bpf_stream_stage_printk(ctxp->ss, "%pS\n  %s @ %s:%d\n",
> > +                                                 (void *)ip, line, file, num);
> > +             return !ctxp->err;
> > +     }
> > +end:
> > +     ctxp->err = bpf_stream_stage_printk(ctxp->ss, "%pS\n", (void *)ip);
> > +     return !ctxp->err;
> > +}
> > +
> > +int bpf_stream_stage_dump_stack(struct bpf_stream_stage *ss)
> > +{
> > +     struct dump_stack_ctx ctx = { .ss = ss };
> > +     int ret;
> > +
> > +     ret = bpf_stream_stage_printk(ss, "CPU: %d UID: %d PID: %d Comm: %s\n",
> > +                                   raw_smp_processor_id(), __kuid_val(current_real_cred()->euid),
> > +                                   current->pid, current->comm);
> > +     ret = ret ?: bpf_stream_stage_printk(ss, "Call trace:\n");
> > +     if (!ret)
> > +             arch_bpf_stack_walk(dump_stack_cb, &ctx);
> > +     ret = ret ?: ctx.err;
> > +     return ret ?: bpf_stream_stage_printk(ss, "\n");
> > +}
> > --
> > 2.47.1
> >
> >

Re: [PATCH bpf-next v3 02/12] bpf: Introduce BPF standard streams

[Jiri Olsa]

On Mon, Jun 23, 2025 at 08:12:42PM -0700, Kumar Kartikeya Dwivedi wrote:
> Add support for a stream API to the kernel and expose related kfuncs to
> BPF programs. Two streams are exposed, BPF_STDOUT and BPF_STDERR. These
> can be used for printing messages that can be consumed from user space,
> thus it's similar in spirit to existing trace_pipe interface.
> 
> The kernel will use the BPF_STDERR stream to notify the program of any
> errors encountered at runtime. BPF programs themselves may use both
> streams for writing debug messages. BPF library-like code may use
> BPF_STDERR to print warnings or errors on misuse at runtime.

just curious, IIUC we can't mix the output of the streams when we dump
them, right? I wonder it'd be handy to be able to get combined output
and see messages from bpf programs sorted out with messages from kernel

thanks,
jirka


> 
> The implementation of a stream is as follows. Everytime a message is
> emitted from the kernel (directly, or through a BPF program), a record
> is allocated by bump allocating from per-cpu region backed by a page
> obtained using try_alloc_pages. This ensures that we can allocate memory
> from any context. The eventual plan is to discard this scheme in favor
> of Alexei's kmalloc_nolock() [0].
> 
> This record is then locklessly inserted into a list (llist_add()) so
> that the printing side doesn't require holding any locks, and works in
> any context. Each stream has a maximum capacity of 4MB of text, and each
> printed message is accounted against this limit.
> 
> Messages from a program are emitted using the bpf_stream_vprintk kfunc,
> which takes a stream_id argument in addition to working otherwise
> similar to bpf_trace_vprintk.
> 
> The bprintf buffer helpers are extracted out to be reused for printing
> the string into them before copying it into the stream, so that we can
> (with the defined max limit) format a string and know its true length
> before performing allocations of the stream element.
> 
> For consuming elements from a stream, we expose a bpf(2) syscall command
> named BPF_PROG_STREAM_READ_BY_FD, which allows reading data from the
> stream of a given prog_fd into a user space buffer. The main logic is
> implemented in bpf_stream_read(). The log messages are queued in
> bpf_stream::log by the bpf_stream_vprintk kfunc, and then pulled and
> ordered correctly in the stream backlog.
> 
> For this purpose, we hold a lock around bpf_stream_backlog_peek(), as
> llist_del_first() (if we maintained a second lockless list for the
> backlog) wouldn't be safe from multiple threads anyway. Then, if we
> fail to find something in the backlog log, we splice out everything from
> the lockless log, and place it in the backlog log, and then return the
> head of the backlog. Once the full length of the element is consumed, we
> will pop it and free it.
> 
> The lockless list bpf_stream::log is a LIFO stack. Elements obtained
> using a llist_del_all() operation are in LIFO order, thus would break
> the chronological ordering if printed directly. Hence, this batch of
> messages is first reversed. Then, it is stashed into a separate list in
> the stream, i.e. the backlog_log. The head of this list is the actual
> message that should always be returned to the caller. All of this is
> done in bpf_stream_backlog_fill().
> 
> From the kernel side, the writing into the stream will be a bit more
> involved than the typical printk. First, the kernel typically may print
> a collection of messages into the stream, and parallel writers into the
> stream may suffer from interleaving of messages. To ensure each group of
> messages is visible atomically, we can lift the advantage of using a
> lockless list for pushing in messages.
> 
> To enable this, we add a bpf_stream_stage() macro, and require kernel
> users to use bpf_stream_printk statements for the passed expression to
> write into the stream. Underneath the macro, we have a message staging
> API, where a bpf_stream_stage object on the stack accumulates the
> messages being printed into a local llist_head, and then a commit
> operation splices the whole batch into the stream's lockless log list.
> 
> This is especially pertinent for rqspinlock deadlock messages printed to
> program streams. After this change, we see each deadlock invocation as a
> non-interleaving contiguous message without any confusion on the
> reader's part, improving their user experience in debugging the fault.
> 
> While programs cannot benefit from this staged stream writing API, they
> could just as well hold an rqspinlock around their print statements to
> serialize messages, hence this is kept kernel-internal for now.
> 
> Overall, this infrastructure provides NMI-safe any context printing of
> messages to two dedicated streams.
> 
> Later patches will add support for printing splats in case of BPF arena
> page faults, rqspinlock deadlocks, and cond_break timeouts, and
> integration of this facility into bpftool for dumping messages to user
> space.
> 
> Make sure that we don't end up spamming too many errors if the program
> keeps failing repeatedly and filling up the stream, hence emit at most
> 512 error messages from the kernel for a given stream.
> 
>   [0]: https://lore.kernel.org/bpf/20250501032718.65476-1-alexei.starovoitov@gmail.com
> 
> Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>  include/linux/bpf.h            |  59 ++++
>  include/uapi/linux/bpf.h       |  24 ++
>  kernel/bpf/Makefile            |   2 +-
>  kernel/bpf/core.c              |   5 +
>  kernel/bpf/helpers.c           |   1 +
>  kernel/bpf/stream.c            | 485 +++++++++++++++++++++++++++++++++
>  kernel/bpf/syscall.c           |  27 +-
>  tools/include/uapi/linux/bpf.h |  24 ++
>  8 files changed, 625 insertions(+), 2 deletions(-)
>  create mode 100644 kernel/bpf/stream.c
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 4fff0cee8622..cdd726cfe622 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1538,6 +1538,36 @@ struct btf_mod_pair {
>  
>  struct bpf_kfunc_desc_tab;
>  
> +enum bpf_stream_id {
> +	BPF_STDOUT = 1,
> +	BPF_STDERR = 2,
> +};
> +
> +struct bpf_stream_elem {
> +	struct llist_node node;
> +	int total_len;
> +	int consumed_len;
> +	char str[];
> +};
> +
> +enum {
> +	BPF_STREAM_MAX_CAPACITY = (4 * 1024U * 1024U),
> +};
> +
> +struct bpf_stream {
> +	atomic_t capacity;
> +	struct llist_head log;	/* list of in-flight stream elements in LIFO order */
> +
> +	struct mutex lock;  /* lock protecting backlog_{head,tail} */
> +	struct llist_node *backlog_head; /* list of in-flight stream elements in FIFO order */
> +	struct llist_node *backlog_tail; /* tail of the list above */
> +};
> +
> +struct bpf_stream_stage {
> +	struct llist_head log;
> +	int len;
> +};
> +
>  struct bpf_prog_aux {
>  	atomic64_t refcnt;
>  	u32 used_map_cnt;
> @@ -1646,6 +1676,8 @@ struct bpf_prog_aux {
>  		struct work_struct work;
>  		struct rcu_head	rcu;
>  	};
> +	struct bpf_stream stream[2];
> +	atomic_t stream_error_cnt;
>  };
>  
>  struct bpf_prog {
> @@ -2408,6 +2440,8 @@ int  generic_map_delete_batch(struct bpf_map *map,
>  struct bpf_map *bpf_map_get_curr_or_next(u32 *id);
>  struct bpf_prog *bpf_prog_get_curr_or_next(u32 *id);
>  
> +
> +struct page *__bpf_alloc_page(int nid);
>  int bpf_map_alloc_pages(const struct bpf_map *map, int nid,
>  			unsigned long nr_pages, struct page **page_array);
>  #ifdef CONFIG_MEMCG
> @@ -3573,6 +3607,31 @@ void bpf_bprintf_cleanup(struct bpf_bprintf_data *data);
>  int bpf_try_get_buffers(struct bpf_bprintf_buffers **bufs);
>  void bpf_put_buffers(void);
>  
> +#define BPF_PROG_STREAM_ERROR_CNT 512
> +
> +void bpf_prog_stream_init(struct bpf_prog *prog);
> +void bpf_prog_stream_free(struct bpf_prog *prog);
> +int bpf_prog_stream_read(struct bpf_prog *prog, enum bpf_stream_id stream_id, void __user *buf, int len);
> +void bpf_stream_stage_init(struct bpf_stream_stage *ss);
> +void bpf_stream_stage_free(struct bpf_stream_stage *ss);
> +__printf(2, 3)
> +int bpf_stream_stage_printk(struct bpf_stream_stage *ss, const char *fmt, ...);
> +int bpf_stream_stage_commit(struct bpf_stream_stage *ss, struct bpf_prog *prog,
> +			    enum bpf_stream_id stream_id);
> +
> +bool bpf_prog_stream_error_limit(struct bpf_prog *prog);
> +
> +#define bpf_stream_printk(ss, ...) bpf_stream_stage_printk(&ss, __VA_ARGS__)
> +
> +#define bpf_stream_stage(ss, prog, stream_id, expr)                      \
> +	({                                                               \
> +		if (!bpf_prog_stream_error_limit(prog)) {                \
> +			bpf_stream_stage_init(&ss);			 \
> +			(expr);                                          \
> +			bpf_stream_stage_commit(&ss, prog, stream_id);	 \
> +			bpf_stream_stage_free(&ss);			 \
> +		}                                                        \
> +	})
>  
>  #ifdef CONFIG_BPF_LSM
>  void bpf_cgroup_atype_get(u32 attach_btf_id, int cgroup_atype);
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 39e7818cca80..f2fce6a94523 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -906,6 +906,17 @@ union bpf_iter_link_info {
>   *		A new file descriptor (a nonnegative integer), or -1 if an
>   *		error occurred (in which case, *errno* is set appropriately).
>   *
> + * BPF_PROG_STREAM_READ_BY_FD
> + *	Description
> + *		Read data of a program's BPF stream. The program is identified
> + *		by *prog_fd*, and the stream is identified by the *stream_id*.
> + *		The data is copied to a buffer pointed to by *stream_buf*, and
> + *		filled less than or equal to *stream_buf_len* bytes.
> + *
> + *	Return
> + *		Number of bytes read from the stream on success, or -1 if an
> + *		error occurred (in which case, *errno* is set appropriately).
> + *
>   * NOTES
>   *	eBPF objects (maps and programs) can be shared between processes.
>   *
> @@ -961,6 +972,7 @@ enum bpf_cmd {
>  	BPF_LINK_DETACH,
>  	BPF_PROG_BIND_MAP,
>  	BPF_TOKEN_CREATE,
> +	BPF_PROG_STREAM_READ_BY_FD,
>  	__MAX_BPF_CMD,
>  };
>  
> @@ -1463,6 +1475,11 @@ struct bpf_stack_build_id {
>  
>  #define BPF_OBJ_NAME_LEN 16U
>  
> +enum {
> +	BPF_STREAM_STDOUT = 1,
> +	BPF_STREAM_STDERR = 2,
> +};
> +
>  union bpf_attr {
>  	struct { /* anonymous struct used by BPF_MAP_CREATE command */
>  		__u32	map_type;	/* one of enum bpf_map_type */
> @@ -1849,6 +1866,13 @@ union bpf_attr {
>  		__u32		bpffs_fd;
>  	} token_create;
>  
> +	struct {
> +		__aligned_u64	stream_buf;
> +		__u32		stream_buf_len;
> +		__u32		stream_id;
> +		__u32		prog_fd;
> +	} prog_stream_read;
> +
>  } __attribute__((aligned(8)));
>  
>  /* The description below is an attempt at providing documentation to eBPF
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index 3a335c50e6e3..269c04a24664 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -14,7 +14,7 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
>  obj-${CONFIG_BPF_LSM}	  += bpf_inode_storage.o
>  obj-$(CONFIG_BPF_SYSCALL) += disasm.o mprog.o
>  obj-$(CONFIG_BPF_JIT) += trampoline.o
> -obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o rqspinlock.o
> +obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o rqspinlock.o stream.o
>  ifeq ($(CONFIG_MMU)$(CONFIG_64BIT),yy)
>  obj-$(CONFIG_BPF_SYSCALL) += arena.o range_tree.o
>  endif
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index e536a34a32c8..f0def24573ae 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -134,6 +134,10 @@ struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flag
>  	mutex_init(&fp->aux->ext_mutex);
>  	mutex_init(&fp->aux->dst_mutex);
>  
> +#ifdef CONFIG_BPF_SYSCALL
> +	bpf_prog_stream_init(fp);
> +#endif
> +
>  	return fp;
>  }
>  
> @@ -2862,6 +2866,7 @@ static void bpf_prog_free_deferred(struct work_struct *work)
>  	aux = container_of(work, struct bpf_prog_aux, work);
>  #ifdef CONFIG_BPF_SYSCALL
>  	bpf_free_kfunc_btf_tab(aux->kfunc_btf_tab);
> +	bpf_prog_stream_free(aux->prog);
>  #endif
>  #ifdef CONFIG_CGROUP_BPF
>  	if (aux->cgroup_atype != CGROUP_BPF_ATTACH_TYPE_INVALID)
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 67d48f9fb173..8fef7b3cbd80 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -3393,6 +3393,7 @@ BTF_ID_FLAGS(func, bpf_iter_dmabuf_next, KF_ITER_NEXT | KF_RET_NULL | KF_SLEEPAB
>  BTF_ID_FLAGS(func, bpf_iter_dmabuf_destroy, KF_ITER_DESTROY | KF_SLEEPABLE)
>  #endif
>  BTF_ID_FLAGS(func, __bpf_trap)
> +BTF_ID_FLAGS(func, bpf_stream_vprintk, KF_TRUSTED_ARGS)
>  BTF_KFUNCS_END(common_btf_ids)
>  
>  static const struct btf_kfunc_id_set common_kfunc_set = {
> diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
> new file mode 100644
> index 000000000000..75ceb6379368
> --- /dev/null
> +++ b/kernel/bpf/stream.c
> @@ -0,0 +1,485 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
> +
> +#include <linux/bpf.h>
> +#include <linux/bpf_mem_alloc.h>
> +#include <linux/percpu.h>
> +#include <linux/refcount.h>
> +#include <linux/gfp.h>
> +#include <linux/memory.h>
> +#include <linux/local_lock.h>
> +#include <linux/mutex.h>
> +
> +/*
> + * Simple per-CPU NMI-safe bump allocation mechanism, backed by the NMI-safe
> + * try_alloc_pages()/free_pages_nolock() primitives. We allocate a page and
> + * stash it in a local per-CPU variable, and bump allocate from the page
> + * whenever items need to be printed to a stream. Each page holds a global
> + * atomic refcount in its first 4 bytes, and then records of variable length
> + * that describe the printed messages. Once the global refcount has dropped to
> + * zero, it is a signal to free the page back to the kernel's page allocator,
> + * given all the individual records in it have been consumed.
> + *
> + * It is possible the same page is used to serve allocations across different
> + * programs, which may be consumed at different times individually, hence
> + * maintaining a reference count per-page is critical for correct lifetime
> + * tracking.
> + *
> + * The bpf_stream_page code will be replaced to use kmalloc_nolock() once it
> + * lands.
> + */
> +struct bpf_stream_page {
> +	refcount_t ref;
> +	u32 consumed;
> +	char buf[];
> +};
> +
> +/* Available room to add data to a refcounted page. */
> +#define BPF_STREAM_PAGE_SZ (PAGE_SIZE - offsetofend(struct bpf_stream_page, consumed))
> +
> +static DEFINE_PER_CPU(local_trylock_t, stream_local_lock) = INIT_LOCAL_TRYLOCK(stream_local_lock);
> +static DEFINE_PER_CPU(struct bpf_stream_page *, stream_pcpu_page);
> +
> +static bool bpf_stream_page_local_lock(unsigned long *flags)
> +{
> +	return local_trylock_irqsave(&stream_local_lock, *flags);
> +}
> +
> +static void bpf_stream_page_local_unlock(unsigned long *flags)
> +{
> +	local_unlock_irqrestore(&stream_local_lock, *flags);
> +}
> +
> +static void bpf_stream_page_free(struct bpf_stream_page *stream_page)
> +{
> +	struct page *p;
> +
> +	if (!stream_page)
> +		return;
> +	p = virt_to_page(stream_page);
> +	free_pages_nolock(p, 0);
> +}
> +
> +static void bpf_stream_page_get(struct bpf_stream_page *stream_page)
> +{
> +	refcount_inc(&stream_page->ref);
> +}
> +
> +static void bpf_stream_page_put(struct bpf_stream_page *stream_page)
> +{
> +	if (refcount_dec_and_test(&stream_page->ref))
> +		bpf_stream_page_free(stream_page);
> +}
> +
> +static void bpf_stream_page_init(struct bpf_stream_page *stream_page)
> +{
> +	refcount_set(&stream_page->ref, 1);
> +	stream_page->consumed = 0;
> +}
> +
> +static struct bpf_stream_page *bpf_stream_page_replace(void)
> +{
> +	struct bpf_stream_page *stream_page, *old_stream_page;
> +	struct page *page;
> +
> +	page = __bpf_alloc_page(NUMA_NO_NODE);
> +	if (!page)
> +		return NULL;
> +	stream_page = page_address(page);
> +	bpf_stream_page_init(stream_page);
> +
> +	old_stream_page = this_cpu_read(stream_pcpu_page);
> +	if (old_stream_page)
> +		bpf_stream_page_put(old_stream_page);
> +	this_cpu_write(stream_pcpu_page, stream_page);
> +	return stream_page;
> +}
> +
> +static int bpf_stream_page_check_room(struct bpf_stream_page *stream_page, int len)
> +{
> +	int min = offsetof(struct bpf_stream_elem, str[0]);
> +	int consumed = stream_page->consumed;
> +	int total = BPF_STREAM_PAGE_SZ;
> +	int rem = max(0, total - consumed - min);
> +
> +	/* Let's give room of at least 8 bytes. */
> +	WARN_ON_ONCE(rem % 8 != 0);
> +	rem = rem < 8 ? 0 : rem;
> +	return min(len, rem);
> +}
> +
> +static void bpf_stream_elem_init(struct bpf_stream_elem *elem, int len)
> +{
> +	init_llist_node(&elem->node);
> +	elem->total_len = len;
> +	elem->consumed_len = 0;
> +}
> +
> +static struct bpf_stream_page *bpf_stream_page_from_elem(struct bpf_stream_elem *elem)
> +{
> +	unsigned long addr = (unsigned long)elem;
> +
> +	return (struct bpf_stream_page *)PAGE_ALIGN_DOWN(addr);
> +}
> +
> +static struct bpf_stream_elem *bpf_stream_page_push_elem(struct bpf_stream_page *stream_page, int len)
> +{
> +	u32 consumed = stream_page->consumed;
> +
> +	stream_page->consumed += round_up(offsetof(struct bpf_stream_elem, str[len]), 8);
> +	return (struct bpf_stream_elem *)&stream_page->buf[consumed];
> +}
> +
> +static noinline struct bpf_stream_elem *bpf_stream_page_reserve_elem(int len)
> +{
> +	struct bpf_stream_elem *elem = NULL;
> +	struct bpf_stream_page *page;
> +	int room = 0;
> +
> +	page = this_cpu_read(stream_pcpu_page);
> +	if (!page)
> +		page = bpf_stream_page_replace();
> +	if (!page)
> +		return NULL;
> +
> +	room = bpf_stream_page_check_room(page, len);
> +	if (room != len)
> +		page = bpf_stream_page_replace();
> +	if (!page)
> +		return NULL;
> +	bpf_stream_page_get(page);
> +	room = bpf_stream_page_check_room(page, len);
> +	WARN_ON_ONCE(room != len);
> +
> +	elem = bpf_stream_page_push_elem(page, room);
> +	bpf_stream_elem_init(elem, room);
> +	return elem;
> +}
> +
> +static struct bpf_stream_elem *bpf_stream_elem_alloc(int len)
> +{
> +	const int max_len = ARRAY_SIZE((struct bpf_bprintf_buffers){}.buf);
> +	struct bpf_stream_elem *elem;
> +	unsigned long flags;
> +
> +	BUILD_BUG_ON(max_len > BPF_STREAM_PAGE_SZ);
> +	/*
> +	 * Length denotes the amount of data to be written as part of stream element,
> +	 * thus includes '\0' byte. We're capped by how much bpf_bprintf_buffers can
> +	 * accomodate, therefore deny allocations that won't fit into them.
> +	 */
> +	if (len < 0 || len > max_len)
> +		return NULL;
> +
> +	if (!bpf_stream_page_local_lock(&flags))
> +		return NULL;
> +	elem = bpf_stream_page_reserve_elem(len);
> +	bpf_stream_page_local_unlock(&flags);
> +	return elem;
> +}
> +
> +static int __bpf_stream_push_str(struct llist_head *log, const char *str, int len)
> +{
> +	struct bpf_stream_elem *elem = NULL;
> +
> +	/*
> +	 * Allocate a bpf_prog_stream_elem and push it to the bpf_prog_stream
> +	 * log, elements will be popped at once and reversed to print the log.
> +	 */
> +	elem = bpf_stream_elem_alloc(len);
> +	if (!elem)
> +		return -ENOMEM;
> +
> +	memcpy(elem->str, str, len);
> +	llist_add(&elem->node, log);
> +
> +	return 0;
> +}
> +
> +static int bpf_stream_consume_capacity(struct bpf_stream *stream, int len)
> +{
> +	if (atomic_read(&stream->capacity) >= BPF_STREAM_MAX_CAPACITY)
> +		return -ENOSPC;
> +	if (atomic_add_return(len, &stream->capacity) >= BPF_STREAM_MAX_CAPACITY) {
> +		atomic_sub(len, &stream->capacity);
> +		return -ENOSPC;
> +	}
> +	return 0;
> +}
> +
> +static void bpf_stream_release_capacity(struct bpf_stream *stream, struct bpf_stream_elem *elem)
> +{
> +	int len = elem->total_len;
> +
> +	atomic_sub(len, &stream->capacity);
> +}
> +
> +static int bpf_stream_push_str(struct bpf_stream *stream, const char *str, int len)
> +{
> +	int ret = bpf_stream_consume_capacity(stream, len);
> +
> +	return ret ?: __bpf_stream_push_str(&stream->log, str, len);
> +}
> +
> +static struct bpf_stream *bpf_stream_get(enum bpf_stream_id stream_id, struct bpf_prog_aux *aux)
> +{
> +	if (stream_id != BPF_STDOUT && stream_id != BPF_STDERR)
> +		return NULL;
> +	return &aux->stream[stream_id - 1];
> +}
> +
> +static void bpf_stream_free_elem(struct bpf_stream_elem *elem)
> +{
> +	struct bpf_stream_page *p;
> +
> +	p = bpf_stream_page_from_elem(elem);
> +	bpf_stream_page_put(p);
> +}
> +
> +static void bpf_stream_free_list(struct llist_node *list)
> +{
> +	struct bpf_stream_elem *elem, *tmp;
> +
> +	llist_for_each_entry_safe(elem, tmp, list, node)
> +		bpf_stream_free_elem(elem);
> +}
> +
> +static struct llist_node *bpf_stream_backlog_peek(struct bpf_stream *stream)
> +{
> +	return stream->backlog_head;
> +}
> +
> +static struct llist_node *bpf_stream_backlog_pop(struct bpf_stream *stream)
> +{
> +	struct llist_node *node;
> +
> +	node = stream->backlog_head;
> +	if (stream->backlog_head == stream->backlog_tail)
> +		stream->backlog_head = stream->backlog_tail = NULL;
> +	else
> +		stream->backlog_head = node->next;
> +	return node;
> +}
> +
> +static void bpf_stream_backlog_fill(struct bpf_stream *stream)
> +{
> +	struct llist_node *head, *tail;
> +
> +	if (llist_empty(&stream->log))
> +		return;
> +	tail = llist_del_all(&stream->log);
> +	if (!tail)
> +		return;
> +	head = llist_reverse_order(tail);
> +
> +	if (!stream->backlog_head) {
> +		stream->backlog_head = head;
> +		stream->backlog_tail = tail;
> +	} else {
> +		stream->backlog_tail->next = head;
> +		stream->backlog_tail = tail;
> +	}
> +
> +	return;
> +}
> +
> +static bool bpf_stream_consume_elem(struct bpf_stream_elem *elem, int *len)
> +{
> +	int rem = elem->total_len - elem->consumed_len;
> +	int used = min(rem, *len);
> +
> +	elem->consumed_len += used;
> +	*len -= used;
> +
> +	return elem->consumed_len == elem->total_len;
> +}
> +
> +static int bpf_stream_read(struct bpf_stream *stream, void __user *buf, int len)
> +{
> +	int rem_len = len, cons_len, ret = 0;
> +	struct bpf_stream_elem *elem = NULL;
> +	struct llist_node *node;
> +
> +	mutex_lock(&stream->lock);
> +
> +	while (rem_len) {
> +		int pos = len - rem_len;
> +		bool cont;
> +
> +		node = bpf_stream_backlog_peek(stream);
> +		if (!node) {
> +			bpf_stream_backlog_fill(stream);
> +			node = bpf_stream_backlog_peek(stream);
> +		}
> +		if (!node)
> +			break;
> +		elem = container_of(node, typeof(*elem), node);
> +
> +		cons_len = elem->consumed_len;
> +		cont = bpf_stream_consume_elem(elem, &rem_len) == false;
> +
> +		ret = copy_to_user(buf + pos, elem->str + cons_len,
> +				   elem->consumed_len - cons_len);
> +		/* Restore in case of error. */
> +		if (ret) {
> +			ret = -EFAULT;
> +			elem->consumed_len = cons_len;
> +			break;
> +		}
> +
> +		if (cont)
> +			continue;
> +		bpf_stream_backlog_pop(stream);
> +		bpf_stream_release_capacity(stream, elem);
> +		bpf_stream_free_elem(elem);
> +	}
> +
> +	mutex_unlock(&stream->lock);
> +	return ret ? ret : len - rem_len;
> +}
> +
> +int bpf_prog_stream_read(struct bpf_prog *prog, enum bpf_stream_id stream_id, void __user *buf, int len)
> +{
> +	struct bpf_stream *stream;
> +
> +	stream = bpf_stream_get(stream_id, prog->aux);
> +	if (!stream)
> +		return -ENOENT;
> +	return bpf_stream_read(stream, buf, len);
> +}
> +
> +__bpf_kfunc_start_defs();
> +
> +/*
> + * Avoid using enum bpf_stream_id so that kfunc users don't have to pull in the
> + * enum in headers.
> + */
> +__bpf_kfunc int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *args, u32 len__sz, void *aux__prog)
> +{
> +	struct bpf_bprintf_data data = {
> +		.get_bin_args	= true,
> +		.get_buf	= true,
> +	};
> +	struct bpf_prog_aux *aux = aux__prog;
> +	u32 fmt_size = strlen(fmt__str) + 1;
> +	struct bpf_stream *stream;
> +	u32 data_len = len__sz;
> +	int ret, num_args;
> +
> +	stream = bpf_stream_get(stream_id, aux);
> +	if (!stream)
> +		return -ENOENT;
> +
> +	if (data_len & 7 || data_len > MAX_BPRINTF_VARARGS * 8 ||
> +	    (data_len && !args))
> +		return -EINVAL;
> +	num_args = data_len / 8;
> +
> +	ret = bpf_bprintf_prepare(fmt__str, fmt_size, args, num_args, &data);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt__str, data.bin_args);
> +	/* If the string was truncated, we only wrote until the size of buffer. */
> +	ret = min_t(u32, ret + 1, MAX_BPRINTF_BUF);
> +	ret = bpf_stream_push_str(stream, data.buf, ret);
> +	bpf_bprintf_cleanup(&data);
> +
> +	return ret;
> +}
> +
> +__bpf_kfunc_end_defs();
> +
> +/* Added kfunc to common_btf_ids */
> +
> +void bpf_prog_stream_init(struct bpf_prog *prog)
> +{
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(prog->aux->stream); i++) {
> +		atomic_set(&prog->aux->stream[i].capacity, 0);
> +		init_llist_head(&prog->aux->stream[i].log);
> +		mutex_init(&prog->aux->stream[i].lock);
> +		prog->aux->stream[i].backlog_head = NULL;
> +		prog->aux->stream[i].backlog_tail = NULL;
> +	}
> +}
> +
> +void bpf_prog_stream_free(struct bpf_prog *prog)
> +{
> +	struct llist_node *list;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(prog->aux->stream); i++) {
> +		list = llist_del_all(&prog->aux->stream[i].log);
> +		bpf_stream_free_list(list);
> +		bpf_stream_free_list(prog->aux->stream[i].backlog_head);
> +	}
> +}
> +
> +void bpf_stream_stage_init(struct bpf_stream_stage *ss)
> +{
> +	init_llist_head(&ss->log);
> +	ss->len = 0;
> +}
> +
> +void bpf_stream_stage_free(struct bpf_stream_stage *ss)
> +{
> +	struct llist_node *node;
> +
> +	node = llist_del_all(&ss->log);
> +	bpf_stream_free_list(node);
> +}
> +
> +int bpf_stream_stage_printk(struct bpf_stream_stage *ss, const char *fmt, ...)
> +{
> +	struct bpf_bprintf_buffers *buf;
> +	va_list args;
> +	int ret;
> +
> +	if (bpf_try_get_buffers(&buf))
> +		return -EBUSY;
> +
> +	va_start(args, fmt);
> +	ret = vsnprintf(buf->buf, ARRAY_SIZE(buf->buf), fmt, args);
> +	va_end(args);
> +	/* If the string was truncated, we only wrote until the size of buffer. */
> +	ret = min_t(u32, ret + 1, ARRAY_SIZE(buf->buf));
> +	ss->len += ret;
> +	ret = __bpf_stream_push_str(&ss->log, buf->buf, ret);
> +	bpf_put_buffers();
> +	return ret;
> +}
> +
> +int bpf_stream_stage_commit(struct bpf_stream_stage *ss, struct bpf_prog *prog,
> +			    enum bpf_stream_id stream_id)
> +{
> +	struct llist_node *list, *head, *tail;
> +	struct bpf_stream *stream;
> +	int ret;
> +
> +	stream = bpf_stream_get(stream_id, prog->aux);
> +	if (!stream)
> +		return -EINVAL;
> +
> +	ret = bpf_stream_consume_capacity(stream, ss->len);
> +	if (ret)
> +		return ret;
> +
> +	list = llist_del_all(&ss->log);
> +	head = tail = list;
> +
> +	if (!list)
> +		return 0;
> +	while (llist_next(list)) {
> +		tail = llist_next(list);
> +		list = tail;
> +	}
> +	llist_add_batch(head, tail, &stream->log);
> +	return 0;
> +}
> +
> +bool bpf_prog_stream_error_limit(struct bpf_prog *prog)
> +{
> +	return atomic_fetch_add(1, &prog->aux->stream_error_cnt) >= BPF_PROG_STREAM_ERROR_CNT;
> +}
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 56500381c28a..ac1010b9d11b 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -576,7 +576,7 @@ static bool can_alloc_pages(void)
>  		!IS_ENABLED(CONFIG_PREEMPT_RT);
>  }
>  
> -static struct page *__bpf_alloc_page(int nid)
> +struct page *__bpf_alloc_page(int nid)
>  {
>  	if (!can_alloc_pages())
>  		return alloc_pages_nolock(nid, 0);
> @@ -5936,6 +5936,28 @@ static int token_create(union bpf_attr *attr)
>  	return bpf_token_create(attr);
>  }
>  
> +#define BPF_PROG_STREAM_READ_BY_FD_LAST_FIELD prog_stream_read.prog_fd
> +
> +static int prog_stream_read(union bpf_attr *attr)
> +{
> +	char __user *buf = u64_to_user_ptr(attr->prog_stream_read.stream_buf);
> +	u32 len = attr->prog_stream_read.stream_buf_len;
> +	struct bpf_prog *prog;
> +	int ret;
> +
> +	if (CHECK_ATTR(BPF_PROG_STREAM_READ_BY_FD))
> +		return -EINVAL;
> +
> +	prog = bpf_prog_get(attr->prog_stream_read.prog_fd);
> +	if (IS_ERR(prog))
> +		return PTR_ERR(prog);
> +
> +	ret = bpf_prog_stream_read(prog, attr->prog_stream_read.stream_id, buf, len);
> +	bpf_prog_put(prog);
> +
> +	return ret;
> +}
> +
>  static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size)
>  {
>  	union bpf_attr attr;
> @@ -6072,6 +6094,9 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size)
>  	case BPF_TOKEN_CREATE:
>  		err = token_create(&attr);
>  		break;
> +	case BPF_PROG_STREAM_READ_BY_FD:
> +		err = prog_stream_read(&attr);
> +		break;
>  	default:
>  		err = -EINVAL;
>  		break;
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 39e7818cca80..f2fce6a94523 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -906,6 +906,17 @@ union bpf_iter_link_info {
>   *		A new file descriptor (a nonnegative integer), or -1 if an
>   *		error occurred (in which case, *errno* is set appropriately).
>   *
> + * BPF_PROG_STREAM_READ_BY_FD
> + *	Description
> + *		Read data of a program's BPF stream. The program is identified
> + *		by *prog_fd*, and the stream is identified by the *stream_id*.
> + *		The data is copied to a buffer pointed to by *stream_buf*, and
> + *		filled less than or equal to *stream_buf_len* bytes.
> + *
> + *	Return
> + *		Number of bytes read from the stream on success, or -1 if an
> + *		error occurred (in which case, *errno* is set appropriately).
> + *
>   * NOTES
>   *	eBPF objects (maps and programs) can be shared between processes.
>   *
> @@ -961,6 +972,7 @@ enum bpf_cmd {
>  	BPF_LINK_DETACH,
>  	BPF_PROG_BIND_MAP,
>  	BPF_TOKEN_CREATE,
> +	BPF_PROG_STREAM_READ_BY_FD,
>  	__MAX_BPF_CMD,
>  };
>  
> @@ -1463,6 +1475,11 @@ struct bpf_stack_build_id {
>  
>  #define BPF_OBJ_NAME_LEN 16U
>  
> +enum {
> +	BPF_STREAM_STDOUT = 1,
> +	BPF_STREAM_STDERR = 2,
> +};
> +
>  union bpf_attr {
>  	struct { /* anonymous struct used by BPF_MAP_CREATE command */
>  		__u32	map_type;	/* one of enum bpf_map_type */
> @@ -1849,6 +1866,13 @@ union bpf_attr {
>  		__u32		bpffs_fd;
>  	} token_create;
>  
> +	struct {
> +		__aligned_u64	stream_buf;
> +		__u32		stream_buf_len;
> +		__u32		stream_id;
> +		__u32		prog_fd;
> +	} prog_stream_read;
> +
>  } __attribute__((aligned(8)));
>  
>  /* The description below is an attempt at providing documentation to eBPF
> -- 
> 2.47.1
> 
> 

Re: [PATCH bpf-next v3 02/12] bpf: Introduce BPF standard streams

[Kumar Kartikeya Dwivedi]

On Tue, 24 Jun 2025 at 14:01, Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Mon, Jun 23, 2025 at 08:12:42PM -0700, Kumar Kartikeya Dwivedi wrote:
> > Add support for a stream API to the kernel and expose related kfuncs to
> > BPF programs. Two streams are exposed, BPF_STDOUT and BPF_STDERR. These
> > can be used for printing messages that can be consumed from user space,
> > thus it's similar in spirit to existing trace_pipe interface.
> >
> > The kernel will use the BPF_STDERR stream to notify the program of any
> > errors encountered at runtime. BPF programs themselves may use both
> > streams for writing debug messages. BPF library-like code may use
> > BPF_STDERR to print warnings or errors on misuse at runtime.
>
> just curious, IIUC we can't mix the output of the streams when we dump
> them, right? I wonder it'd be handy to be able to get combined output
> and see messages from bpf programs sorted out with messages from kernel
>

Yeah, this is a good point.
Right now, no, in the sense that sequentiality is definitely broken
across the two streams.
We can force print a timestamp for every message and do the sorting
from bpftool side, or it can just be piped to sort after dumping both
stdout and stderr.
Output will look like trace_pipe with some fixed format before the
actual message.
WDYT? Others are also welcome to chime in.

> thanks,
> jirka
>
>
> > [...]

Re: [PATCH bpf-next v3 02/12] bpf: Introduce BPF standard streams

[Jiri Olsa]

On Tue, Jun 24, 2025 at 02:15:09PM +0200, Kumar Kartikeya Dwivedi wrote:
> On Tue, 24 Jun 2025 at 14:01, Jiri Olsa <olsajiri@gmail.com> wrote:
> >
> > On Mon, Jun 23, 2025 at 08:12:42PM -0700, Kumar Kartikeya Dwivedi wrote:
> > > Add support for a stream API to the kernel and expose related kfuncs to
> > > BPF programs. Two streams are exposed, BPF_STDOUT and BPF_STDERR. These
> > > can be used for printing messages that can be consumed from user space,
> > > thus it's similar in spirit to existing trace_pipe interface.
> > >
> > > The kernel will use the BPF_STDERR stream to notify the program of any
> > > errors encountered at runtime. BPF programs themselves may use both
> > > streams for writing debug messages. BPF library-like code may use
> > > BPF_STDERR to print warnings or errors on misuse at runtime.
> >
> > just curious, IIUC we can't mix the output of the streams when we dump
> > them, right? I wonder it'd be handy to be able to get combined output
> > and see messages from bpf programs sorted out with messages from kernel
> >
> 
> Yeah, this is a good point.
> Right now, no, in the sense that sequentiality is definitely broken
> across the two streams.
> We can force print a timestamp for every message and do the sorting
> from bpftool side, or it can just be piped to sort after dumping both
> stdout and stderr.
> Output will look like trace_pipe with some fixed format before the
> actual message.
> WDYT? Others are also welcome to chime in.

yes, keeping the kernel simple (just adding timestamp) and sorting
it in bpftool seems good to me

jirka

Re: [PATCH bpf-next v3 02/12] bpf: Introduce BPF standard streams

[Alexei Starovoitov]

On Tue, Jun 24, 2025 at 6:34 AM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Tue, Jun 24, 2025 at 02:15:09PM +0200, Kumar Kartikeya Dwivedi wrote:
> > On Tue, 24 Jun 2025 at 14:01, Jiri Olsa <olsajiri@gmail.com> wrote:
> > >
> > > On Mon, Jun 23, 2025 at 08:12:42PM -0700, Kumar Kartikeya Dwivedi wrote:
> > > > Add support for a stream API to the kernel and expose related kfuncs to
> > > > BPF programs. Two streams are exposed, BPF_STDOUT and BPF_STDERR. These
> > > > can be used for printing messages that can be consumed from user space,
> > > > thus it's similar in spirit to existing trace_pipe interface.
> > > >
> > > > The kernel will use the BPF_STDERR stream to notify the program of any
> > > > errors encountered at runtime. BPF programs themselves may use both
> > > > streams for writing debug messages. BPF library-like code may use
> > > > BPF_STDERR to print warnings or errors on misuse at runtime.
> > >
> > > just curious, IIUC we can't mix the output of the streams when we dump
> > > them, right? I wonder it'd be handy to be able to get combined output
> > > and see messages from bpf programs sorted out with messages from kernel
> > >
> >
> > Yeah, this is a good point.
> > Right now, no, in the sense that sequentiality is definitely broken
> > across the two streams.
> > We can force print a timestamp for every message and do the sorting
> > from bpftool side, or it can just be piped to sort after dumping both
> > stdout and stderr.
> > Output will look like trace_pipe with some fixed format before the
> > actual message.
> > WDYT? Others are also welcome to chime in.
>
> yes, keeping the kernel simple (just adding timestamp) and sorting
> it in bpftool seems good to me

I don't see the point in all that complication.
If bpf prog wants to separate its printk vs kernel printks
it should use a different stream.
Right now there is only stdout and stderr.
Eventually we will allow for more.

Re: [PATCH bpf-next v3 04/12] bpf: Ensure RCU lock is held around bpf_prog_ksym_find

[Alexei Starovoitov]

On Mon, Jun 23, 2025 at 8:13 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> Add a warning to ensure RCU lock is held around tree lookup, and then
> fix one of the invocations in bpf_stack_walker. The program has an
> active stack frame and won't disappear.
>
> Fixes: f18b03fabaa9 ("bpf: Implement BPF exceptions")
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>  kernel/bpf/core.c    | 5 ++++-
>  kernel/bpf/helpers.c | 2 ++
>  2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 5c6e9fbb5508..b4203f68cf33 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -782,7 +782,10 @@ bool is_bpf_text_address(unsigned long addr)
>
>  struct bpf_prog *bpf_prog_ksym_find(unsigned long addr)
>  {
> -       struct bpf_ksym *ksym = bpf_ksym_find(addr);
> +       struct bpf_ksym *ksym;
> +
> +       WARN_ON_ONCE(!rcu_read_lock_held());
> +       ksym = bpf_ksym_find(addr);
>
>         return ksym && ksym->prog ?
>                container_of(ksym, struct bpf_prog_aux, ksym)->prog :
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 8fef7b3cbd80..61b69eb08c4a 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2936,7 +2936,9 @@ static bool bpf_stack_walker(void *cookie, u64 ip, u64 sp, u64 bp)
>
>         if (!is_bpf_text_address(ip))
>                 return !ctx->cnt;
> +       rcu_read_lock();
>         prog = bpf_prog_ksym_find(ip);
> +       rcu_read_unlock();

Please add a comment here explaining that rcu lock protects
struct latch_tree_root bpf_tree access
and returned prog pointer won't disappear.
Otherwise the rcu lock usage looks highly suspicious.

Re: [PATCH bpf-next v3 05/12] bpf: Add function to find program from stack trace

[Alexei Starovoitov]

On Mon, Jun 23, 2025 at 8:13 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> In preparation of figuring out the closest program that led to the
> current point in the kernel, implement a function that scans through the
> stack trace and finds out the closest BPF program when walking down the
> stack trace.
>
> Special care needs to be taken to skip over kernel and BPF subprog
> frames. We basically scan until we find a BPF main prog frame. The
> assumption is that if a program calls into us transitively, we'll
> hit it along the way. If not, we end up returning NULL.
>
> Contextually the function will be used in places where we know the
> program may have called into us.
>
> Due to reliance on arch_bpf_stack_walk(), this function only works on
> x86 with CONFIG_UNWINDER_ORC, arm64, and s390. Remove the warning from
> arch_bpf_stack_walk as well since we call it outside bpf_throw()
> context.
>
> Acked-by: Eduard Zingerman <eddyz87@gmail.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>  arch/x86/net/bpf_jit_comp.c |  1 -
>  include/linux/bpf.h         |  1 +
>  kernel/bpf/core.c           | 28 ++++++++++++++++++++++++++++
>  3 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 15672cb926fc..40e1b3b9634f 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -3845,7 +3845,6 @@ void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp
>         }
>         return;
>  #endif
> -       WARN(1, "verification of programs using bpf_throw should have failed\n");
>  }
>
>  void bpf_arch_poke_desc_update(struct bpf_jit_poke_descriptor *poke,
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f30697c72ba9..cc14ff8e0b88 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -3669,5 +3669,6 @@ static inline bool bpf_is_subprog(const struct bpf_prog *prog)
>
>  int bpf_prog_get_file_line(struct bpf_prog *prog, unsigned long ip, const char **filep,
>                            const char **linep, int *nump);
> +struct bpf_prog *bpf_prog_find_from_stack(void);
>
>  #endif /* _LINUX_BPF_H */
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index b4203f68cf33..3871d817396d 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -3262,4 +3262,32 @@ int bpf_prog_get_file_line(struct bpf_prog *prog, unsigned long ip, const char *
>         return 0;
>  }
>
> +struct walk_stack_ctx {
> +       struct bpf_prog *prog;
> +};
> +
> +static bool find_from_stack_cb(void *cookie, u64 ip, u64 sp, u64 bp)
> +{
> +       struct walk_stack_ctx *ctxp = cookie;
> +       struct bpf_prog *prog;
> +
> +       rcu_read_lock();
> +       prog = bpf_prog_ksym_find(ip);
> +       rcu_read_unlock();

Same here.
Otherwise it looks like an rcu noob mistake.

> +       if (!prog)
> +               return true;
> +       if (bpf_is_subprog(prog))
> +               return true;
> +       ctxp->prog = prog;
> +       return false;
> +}
> +
> +struct bpf_prog *bpf_prog_find_from_stack(void)
> +{
> +       struct walk_stack_ctx ctx = {};
> +
> +       arch_bpf_stack_walk(find_from_stack_cb, &ctx);
> +       return ctx.prog;
> +}
> +
>  #endif
> --
> 2.47.1
>

Re: [PATCH bpf-next v3 02/12] bpf: Introduce BPF standard streams

[Alexei Starovoitov]

On Mon, Jun 23, 2025 at 8:13 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> +
> +static struct bpf_stream_page *bpf_stream_page_replace(void)
> +{
> +       struct bpf_stream_page *stream_page, *old_stream_page;
> +       struct page *page;
> +
> +       page = __bpf_alloc_page(NUMA_NO_NODE);
> +       if (!page)
> +               return NULL;

__bpf_alloc_page() is using GFP_ACCOUNT in both nolock and normal cases,
but active_memcg is random at this point, so the page accounting
is incorrect.
I think we need to remember objcg in prog_aux similar to what
we do with maps, and then store that in bpf_stream and stream_stage
objects in corresponding init() functions.
Then do set_active_memcg() here the way we do in bpf_mem_alloc
and in map_*alloc()s.

Or use alloc_page_nolock() directly here without GFP_ACCOUNT.

Also I think it's strange to limit kernel messages to 4M,
since the kernel messages are essential debug info.
While it makes sense to limit kfunc's spam.
I suspect the idea here is to avoid OOM if the kernel is spammy
due to malicious bpf prog that forces the kernel to warn so much?
But dmesg doesn't do it.
And 4M * 2 * number_of_progs can be many gigabytes.

Maybe let's drop stream->capacity and rely on memcg to limit
the spam for both kernel and kfunc?
Accounting a page at a time seems sufficient.

> +       ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt__str, data.bin_args);
> +       /* If the string was truncated, we only wrote until the size of buffer. */
> +       ret = min_t(u32, ret + 1, MAX_BPRINTF_BUF);
> +       ret = bpf_stream_push_str(stream, data.buf, ret);

We discussed it offline, so mentioning here for the list.
Let's not emit \0 into the stream. Looks unnecessary.

Re: [PATCH bpf-next v3 09/12] libbpf: Add bpf_stream_printk() macro

[Andrii Nakryiko]

On Mon, Jun 23, 2025 at 8:13 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> Add a convenience macro to print data to the BPF streams. BPF_STDOUT and
> BPF_STDERR stream IDs in the vmlinux.h can be passed to the macro to
> print to the respective streams.
>
> Acked-by: Eduard Zingerman <eddyz87@gmail.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>  tools/lib/bpf/bpf_helpers.h | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>

Acked-by: Andrii Nakryiko <andrii@kernel.org>

> diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
> index a50773d4616e..76b127a9f24d 100644
> --- a/tools/lib/bpf/bpf_helpers.h
> +++ b/tools/lib/bpf/bpf_helpers.h
> @@ -314,6 +314,22 @@ enum libbpf_tristate {
>                           ___param, sizeof(___param));          \
>  })
>
> +extern int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *args,
> +                             __u32 len__sz, void *aux__prog) __weak __ksym;
> +
> +#define bpf_stream_printk(stream_id, fmt, args...)                             \
> +({                                                                             \
> +       static const char ___fmt[] = fmt;                                       \
> +       unsigned long long ___param[___bpf_narg(args)];                         \
> +                                                                               \
> +       _Pragma("GCC diagnostic push")                                          \
> +       _Pragma("GCC diagnostic ignored \"-Wint-conversion\"")                  \
> +       ___bpf_fill(___param, args);                                            \
> +       _Pragma("GCC diagnostic pop")                                           \
> +                                                                               \
> +       bpf_stream_vprintk(stream_id, ___fmt, ___param, sizeof(___param), NULL);\
> +})
> +
>  /* Use __bpf_printk when bpf_printk call has 3 or fewer fmt args
>   * Otherwise use __bpf_vprintk
>   */
> --
> 2.47.1
>