[PATCH v6 bpf-next 0/5] bpf: Add bpf_iter_cpumask

[PATCH v6 bpf-next 0/5] bpf: Add bpf_iter_cpumask

[Yafang Shao]

Three new kfuncs, namely bpf_iter_cpumask_{new,next,destroy}, have been
added for the new bpf_iter_cpumask functionality. These kfuncs enable the
iteration of percpu data, such as runqueues, system_group_pcpu, and more.

In our specific use case, we leverage the cgroup iterator to traverse
percpu data, subsequently exposing it to userspace through a seq file.
Refer to example in patch #2 for the usage.

Changes:
- v5 -> v6:
  - Various improvements on the comments (Andrii)
  - Use a static function instead as Kumar's patch[0] has been merged.
    (Anrii, Yonghong) 

[0]. https://lore.kernel.org/bpf/170719262630.31872.2248639771567354367.git-patchwork-notify@kernel.org

- v4 -> v5:
  - Use cpumask_size() instead of sizeof(struct cpumask) (David)
  - Refactor the selftests as suggsted by David
  - Improve the doc as suggested by David
- v3 -> v4:
  - Use a copy of cpumask to avoid potential use-after-free (Yonghong)
  - Various code improvement in selftests (Yonghong)
- v2 -> v3:
  - Define KF_RCU_PROTECTED for bpf_iter_cpumask_new (Alexei)
  - Code improvement in selftests
  - Fix build error in selftest due to CONFIG_PSI=n
    reported by kernel test robot <lkp@intel.com>
- v1 -> v2: 
  - Avoid changing cgroup subsystem (Tejun)
  - Remove bpf_cpumask_set_from_pid(), and use bpf_cpumask_copy()
    instead (Tejun)
  - Use `int cpu;` field in bpf_iter_cpumask_kern (Andrii)

Yafang Shao (5):
  bpf: Add bpf_iter_cpumask kfuncs
  bpf, docs: Add document for cpumask iter
  selftests/bpf: Fix error checking for cpumask_success__load()
  selftests/bpf: Mark cpumask kfunc declarations as __weak
  selftests/bpf: Add selftests for cpumask iter

 Documentation/bpf/cpumasks.rst                |  60 +++++++
 kernel/bpf/cpumask.c                          |  79 +++++++++
 tools/testing/selftests/bpf/config            |   1 +
 .../selftests/bpf/prog_tests/cpumask.c        | 158 +++++++++++++++++-
 .../selftests/bpf/progs/cpumask_common.h      |  60 +++----
 .../bpf/progs/cpumask_iter_failure.c          |  99 +++++++++++
 .../bpf/progs/cpumask_iter_success.c          | 126 ++++++++++++++
 7 files changed, 552 insertions(+), 31 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_failure.c
 create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_success.c

-- 
2.39.1

[PATCH v6 bpf-next 1/5] bpf: Add bpf_iter_cpumask kfuncs

[Yafang Shao]

Add three new kfuncs for bpf_iter_cpumask.
- bpf_iter_cpumask_new
  KF_RCU is defined because the cpumask must be a RCU trusted pointer
  such as task->cpus_ptr.
- bpf_iter_cpumask_next
- bpf_iter_cpumask_destroy

These new kfuncs facilitate the iteration of percpu data, such as
runqueues, psi_cgroup_cpu, and more.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 kernel/bpf/cpumask.c | 79 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
index dad0fb1c8e87..ed6078cfa40e 100644
--- a/kernel/bpf/cpumask.c
+++ b/kernel/bpf/cpumask.c
@@ -422,6 +422,82 @@ __bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask)
 	return cpumask_weight(cpumask);
 }
 
+struct bpf_iter_cpumask {
+	__u64 __opaque[2];
+} __aligned(8);
+
+struct bpf_iter_cpumask_kern {
+	struct cpumask *mask;
+	int cpu;
+} __aligned(8);
+
+/**
+ * bpf_iter_cpumask_new() - Initialize a new CPU mask iterator for a given CPU mask
+ * @it: The new bpf_iter_cpumask to be created.
+ * @mask: The cpumask to be iterated over.
+ *
+ * This function initializes a new bpf_iter_cpumask structure for iterating over
+ * the specified CPU mask. It assigns the provided cpumask to the newly created
+ * bpf_iter_cpumask @it for subsequent iteration operations.
+ *
+ * On success, 0 is returned. On failure, ERR is returned.
+ */
+__bpf_kfunc int bpf_iter_cpumask_new(struct bpf_iter_cpumask *it, const struct cpumask *mask)
+{
+	struct bpf_iter_cpumask_kern *kit = (void *)it;
+
+	BUILD_BUG_ON(sizeof(struct bpf_iter_cpumask_kern) > sizeof(struct bpf_iter_cpumask));
+	BUILD_BUG_ON(__alignof__(struct bpf_iter_cpumask_kern) !=
+		     __alignof__(struct bpf_iter_cpumask));
+
+	kit->mask = bpf_mem_alloc(&bpf_global_ma, cpumask_size());
+	if (!kit->mask)
+		return -ENOMEM;
+
+	cpumask_copy(kit->mask, mask);
+	kit->cpu = -1;
+	return 0;
+}
+
+/**
+ * bpf_iter_cpumask_next() - Get the next CPU in a bpf_iter_cpumask
+ * @it: The bpf_iter_cpumask
+ *
+ * This function returns a pointer to a number representing the ID of the
+ * next CPU in CPU mask. It allows sequential access to CPUs within the
+ * cpumask. If there are no further CPUs available, it returns NULL.
+ */
+__bpf_kfunc int *bpf_iter_cpumask_next(struct bpf_iter_cpumask *it)
+{
+	struct bpf_iter_cpumask_kern *kit = (void *)it;
+	const struct cpumask *mask = kit->mask;
+	int cpu;
+
+	if (!mask)
+		return NULL;
+	cpu = cpumask_next(kit->cpu, mask);
+	if (cpu >= nr_cpu_ids)
+		return NULL;
+
+	kit->cpu = cpu;
+	return &kit->cpu;
+}
+
+/**
+ * bpf_iter_cpumask_destroy() - Destroy a bpf_iter_cpumask
+ * @it: The bpf_iter_cpumask to be destroyed.
+ *
+ * Destroy the resource associated with the bpf_iter_cpumask.
+ */
+__bpf_kfunc void bpf_iter_cpumask_destroy(struct bpf_iter_cpumask *it)
+{
+	struct bpf_iter_cpumask_kern *kit = (void *)it;
+
+	if (!kit->mask)
+		return;
+	bpf_mem_free(&bpf_global_ma, kit->mask);
+}
+
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(cpumask_kfunc_btf_ids)
@@ -450,6 +526,9 @@ BTF_ID_FLAGS(func, bpf_cpumask_copy, KF_RCU)
 BTF_ID_FLAGS(func, bpf_cpumask_any_distribute, KF_RCU)
 BTF_ID_FLAGS(func, bpf_cpumask_any_and_distribute, KF_RCU)
 BTF_ID_FLAGS(func, bpf_cpumask_weight, KF_RCU)
+BTF_ID_FLAGS(func, bpf_iter_cpumask_new, KF_ITER_NEW | KF_RCU)
+BTF_ID_FLAGS(func, bpf_iter_cpumask_next, KF_ITER_NEXT | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_cpumask_destroy, KF_ITER_DESTROY)
 BTF_KFUNCS_END(cpumask_kfunc_btf_ids)
 
 static const struct btf_kfunc_id_set cpumask_kfunc_set = {
-- 
2.39.1

[PATCH v6 bpf-next 2/5] bpf, docs: Add document for cpumask iter

[Yafang Shao]

This patch adds the document for the newly added cpumask iterator
kfuncs.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
---
 Documentation/bpf/cpumasks.rst | 60 ++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/Documentation/bpf/cpumasks.rst b/Documentation/bpf/cpumasks.rst
index b5d47a04da5d..5cedd719874c 100644
--- a/Documentation/bpf/cpumasks.rst
+++ b/Documentation/bpf/cpumasks.rst
@@ -372,6 +372,66 @@ used.
 .. _tools/testing/selftests/bpf/progs/cpumask_success.c:
    https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/progs/cpumask_success.c
 
+3.3 cpumask iterator
+--------------------
+
+The cpumask iterator facilitates the iteration of per-CPU data, including
+runqueues, system_group_pcpu, and other such structures. To leverage the cpumask
+iterator, one can employ the bpf_for_each() macro.
+
+Here's an example illustrating how to determine the number of running tasks on
+each CPU.
+
+.. code-block:: c
+
+        /**
+         * Here's an example demonstrating the functionality of the cpumask iterator.
+         * We retrieve the cpumask associated with the specified pid, iterate through
+         * its elements, and ultimately expose per-CPU data to userspace through a
+         * seq file.
+         */
+        const struct rq runqueues __ksym __weak;
+        u32 target_pid;
+
+        SEC("iter/cgroup")
+        int BPF_PROG(cpu_cgroup, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+        {
+                u32 nr_running = 0, nr_cpus = 0, nr_null_rq = 0;
+                struct task_struct *p;
+                struct rq *rq;
+                int *cpu;
+
+                /* epilogue */
+                if (cgrp == NULL)
+                        return 0;
+
+                p = bpf_task_from_pid(target_pid);
+                if (!p)
+                        return 1;
+
+                BPF_SEQ_PRINTF(meta->seq, "%4s %s\n", "CPU", "nr_running");
+                bpf_for_each(cpumask, cpu, p->cpus_ptr) {
+                        rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, *cpu);
+                        if (!rq) {
+                                nr_null_rq += 1;
+                                continue;
+                        }
+                        nr_cpus += 1;
+
+                        if (!rq->nr_running)
+                                continue;
+
+                        nr_running += rq->nr_running;
+                        BPF_SEQ_PRINTF(meta->seq, "%4u %u\n", *cpu, rq->nr_running);
+                }
+                BPF_SEQ_PRINTF(meta->seq, "Summary: nr_cpus %u, nr_running %u, nr_null_rq %u\n",
+                               nr_cpus, nr_running, nr_null_rq);
+
+                bpf_task_release(p);
+                return 0;
+        }
+
+----
 
 4. Adding BPF cpumask kfuncs
 ============================
-- 
2.39.1

[PATCH v6 bpf-next 3/5] selftests/bpf: Fix error checking for cpumask_success__load()

[Yafang Shao]

We should verify the return value of cpumask_success__load().

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Cc: David Vernet <void@manifault.com>
---
 tools/testing/selftests/bpf/prog_tests/cpumask.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/cpumask.c b/tools/testing/selftests/bpf/prog_tests/cpumask.c
index c2e886399e3c..ecf89df78109 100644
--- a/tools/testing/selftests/bpf/prog_tests/cpumask.c
+++ b/tools/testing/selftests/bpf/prog_tests/cpumask.c
@@ -27,7 +27,7 @@ static void verify_success(const char *prog_name)
 	struct bpf_program *prog;
 	struct bpf_link *link = NULL;
 	pid_t child_pid;
-	int status;
+	int status, err;
 
 	skel = cpumask_success__open();
 	if (!ASSERT_OK_PTR(skel, "cpumask_success__open"))
@@ -36,8 +36,8 @@ static void verify_success(const char *prog_name)
 	skel->bss->pid = getpid();
 	skel->bss->nr_cpus = libbpf_num_possible_cpus();
 
-	cpumask_success__load(skel);
-	if (!ASSERT_OK_PTR(skel, "cpumask_success__load"))
+	err = cpumask_success__load(skel);
+	if (!ASSERT_OK(err, "cpumask_success__load"))
 		goto cleanup;
 
 	prog = bpf_object__find_program_by_name(skel->obj, prog_name);
-- 
2.39.1

[PATCH v6 bpf-next 4/5] selftests/bpf: Mark cpumask kfunc declarations as __weak

[Yafang Shao]

After the series "Annotate kfuncs in .BTF_ids section"[0], kfuncs can be
generated from bpftool. Let's mark the existing cpumask kfunc declarations
__weak so they don't conflict with definitions that will eventually come
from vmlinux.h.

[0]. https://lore.kernel.org/all/cover.1706491398.git.dxu@dxuuu.xyz

Suggested-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Daniel Xu <dxu@dxuuu.xyz>
---
 .../selftests/bpf/progs/cpumask_common.h      | 57 ++++++++++---------
 1 file changed, 29 insertions(+), 28 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/cpumask_common.h b/tools/testing/selftests/bpf/progs/cpumask_common.h
index 0cd4aebb97cf..c705d8112a35 100644
--- a/tools/testing/selftests/bpf/progs/cpumask_common.h
+++ b/tools/testing/selftests/bpf/progs/cpumask_common.h
@@ -23,41 +23,42 @@ struct array_map {
 	__uint(max_entries, 1);
 } __cpumask_map SEC(".maps");
 
-struct bpf_cpumask *bpf_cpumask_create(void) __ksym;
-void bpf_cpumask_release(struct bpf_cpumask *cpumask) __ksym;
-struct bpf_cpumask *bpf_cpumask_acquire(struct bpf_cpumask *cpumask) __ksym;
-u32 bpf_cpumask_first(const struct cpumask *cpumask) __ksym;
-u32 bpf_cpumask_first_zero(const struct cpumask *cpumask) __ksym;
+struct bpf_cpumask *bpf_cpumask_create(void) __ksym __weak;
+void bpf_cpumask_release(struct bpf_cpumask *cpumask) __ksym __weak;
+struct bpf_cpumask *bpf_cpumask_acquire(struct bpf_cpumask *cpumask) __ksym __weak;
+u32 bpf_cpumask_first(const struct cpumask *cpumask) __ksym __weak;
+u32 bpf_cpumask_first_zero(const struct cpumask *cpumask) __ksym __weak;
 u32 bpf_cpumask_first_and(const struct cpumask *src1,
-			  const struct cpumask *src2) __ksym;
-void bpf_cpumask_set_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym;
-void bpf_cpumask_clear_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym;
-bool bpf_cpumask_test_cpu(u32 cpu, const struct cpumask *cpumask) __ksym;
-bool bpf_cpumask_test_and_set_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym;
-bool bpf_cpumask_test_and_clear_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym;
-void bpf_cpumask_setall(struct bpf_cpumask *cpumask) __ksym;
-void bpf_cpumask_clear(struct bpf_cpumask *cpumask) __ksym;
+			  const struct cpumask *src2) __ksym __weak;
+void bpf_cpumask_set_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym __weak;
+void bpf_cpumask_clear_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym __weak;
+bool bpf_cpumask_test_cpu(u32 cpu, const struct cpumask *cpumask) __ksym __weak;
+bool bpf_cpumask_test_and_set_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym __weak;
+bool bpf_cpumask_test_and_clear_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym __weak;
+void bpf_cpumask_setall(struct bpf_cpumask *cpumask) __ksym __weak;
+void bpf_cpumask_clear(struct bpf_cpumask *cpumask) __ksym __weak;
 bool bpf_cpumask_and(struct bpf_cpumask *cpumask,
 		     const struct cpumask *src1,
-		     const struct cpumask *src2) __ksym;
+		     const struct cpumask *src2) __ksym __weak;
 void bpf_cpumask_or(struct bpf_cpumask *cpumask,
 		    const struct cpumask *src1,
-		    const struct cpumask *src2) __ksym;
+		    const struct cpumask *src2) __ksym __weak;
 void bpf_cpumask_xor(struct bpf_cpumask *cpumask,
 		     const struct cpumask *src1,
-		     const struct cpumask *src2) __ksym;
-bool bpf_cpumask_equal(const struct cpumask *src1, const struct cpumask *src2) __ksym;
-bool bpf_cpumask_intersects(const struct cpumask *src1, const struct cpumask *src2) __ksym;
-bool bpf_cpumask_subset(const struct cpumask *src1, const struct cpumask *src2) __ksym;
-bool bpf_cpumask_empty(const struct cpumask *cpumask) __ksym;
-bool bpf_cpumask_full(const struct cpumask *cpumask) __ksym;
-void bpf_cpumask_copy(struct bpf_cpumask *dst, const struct cpumask *src) __ksym;
-u32 bpf_cpumask_any_distribute(const struct cpumask *src) __ksym;
-u32 bpf_cpumask_any_and_distribute(const struct cpumask *src1, const struct cpumask *src2) __ksym;
-u32 bpf_cpumask_weight(const struct cpumask *cpumask) __ksym;
-
-void bpf_rcu_read_lock(void) __ksym;
-void bpf_rcu_read_unlock(void) __ksym;
+		     const struct cpumask *src2) __ksym __weak;
+bool bpf_cpumask_equal(const struct cpumask *src1, const struct cpumask *src2) __ksym __weak;
+bool bpf_cpumask_intersects(const struct cpumask *src1, const struct cpumask *src2) __ksym __weak;
+bool bpf_cpumask_subset(const struct cpumask *src1, const struct cpumask *src2) __ksym __weak;
+bool bpf_cpumask_empty(const struct cpumask *cpumask) __ksym __weak;
+bool bpf_cpumask_full(const struct cpumask *cpumask) __ksym __weak;
+void bpf_cpumask_copy(struct bpf_cpumask *dst, const struct cpumask *src) __ksym __weak;
+u32 bpf_cpumask_any_distribute(const struct cpumask *src) __ksym __weak;
+u32 bpf_cpumask_any_and_distribute(const struct cpumask *src1,
+				   const struct cpumask *src2) __ksym __weak;
+u32 bpf_cpumask_weight(const struct cpumask *cpumask) __ksym __weak;
+
+void bpf_rcu_read_lock(void) __ksym __weak;
+void bpf_rcu_read_unlock(void) __ksym __weak;
 
 static inline const struct cpumask *cast(struct bpf_cpumask *cpumask)
 {
-- 
2.39.1

[PATCH v6 bpf-next 5/5] selftests/bpf: Add selftests for cpumask iter

[Yafang Shao]

Add selftests for the newly added cpumask iter.
- cpumask_iter_success
  - The number of CPUs should be expected when iterating over the cpumask
  - percpu data extracted from the percpu struct should be expected
  - It can work in both non-sleepable and sleepable prog
  - RCU lock is only required by bpf_iter_cpumask_new()
  - It is fine without calling bpf_iter_cpumask_next()

- cpumask_iter_failure
  - RCU lock is required in sleepable prog
  - The cpumask to be iterated over can't be NULL
  - bpf_iter_cpumask_destroy() is required after calling
    bpf_iter_cpumask_new()
  - bpf_iter_cpumask_destroy() can only destroy an initialized iter
  - bpf_iter_cpumask_next() must use an initialized iter

The result as follows,

  #64/37   cpumask/test_cpumask_iter:OK
  #64/38   cpumask/test_cpumask_iter_sleepable:OK
  #64/39   cpumask/test_cpumask_iter_sleepable:OK
  #64/40   cpumask/test_cpumask_iter_next_no_rcu:OK
  #64/41   cpumask/test_cpumask_iter_no_next:OK
  #64/42   cpumask/test_cpumask_iter:OK
  #64/43   cpumask/test_cpumask_iter_no_rcu:OK
  #64/44   cpumask/test_cpumask_iter_no_destroy:OK
  #64/45   cpumask/test_cpumask_iter_null_pointer:OK
  #64/46   cpumask/test_cpumask_iter_next_uninit:OK
  #64/47   cpumask/test_cpumask_iter_destroy_uninit:OK
  #64      cpumask:OK

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 tools/testing/selftests/bpf/config            |   1 +
 .../selftests/bpf/prog_tests/cpumask.c        | 152 ++++++++++++++++++
 .../selftests/bpf/progs/cpumask_common.h      |   3 +
 .../bpf/progs/cpumask_iter_failure.c          |  99 ++++++++++++
 .../bpf/progs/cpumask_iter_success.c          | 126 +++++++++++++++
 5 files changed, 381 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_failure.c
 create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_success.c

diff --git a/tools/testing/selftests/bpf/config b/tools/testing/selftests/bpf/config
index 01f241ea2c67..dd4b0935e35f 100644
--- a/tools/testing/selftests/bpf/config
+++ b/tools/testing/selftests/bpf/config
@@ -78,6 +78,7 @@ CONFIG_NF_CONNTRACK_MARK=y
 CONFIG_NF_DEFRAG_IPV4=y
 CONFIG_NF_DEFRAG_IPV6=y
 CONFIG_NF_NAT=y
+CONFIG_PSI=y
 CONFIG_RC_CORE=y
 CONFIG_SECURITY=y
 CONFIG_SECURITYFS=y
diff --git a/tools/testing/selftests/bpf/prog_tests/cpumask.c b/tools/testing/selftests/bpf/prog_tests/cpumask.c
index ecf89df78109..78423745689c 100644
--- a/tools/testing/selftests/bpf/prog_tests/cpumask.c
+++ b/tools/testing/selftests/bpf/prog_tests/cpumask.c
@@ -1,9 +1,15 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
 
+#define _GNU_SOURCE
+#include <sched.h>
+
 #include <test_progs.h>
 #include "cpumask_failure.skel.h"
 #include "cpumask_success.skel.h"
+#include "cpumask_iter_success.skel.h"
+#include "cpumask_iter_failure.skel.h"
+#include "cgroup_helpers.h"
 
 static const char * const cpumask_success_testcases[] = {
 	"test_alloc_free_cpumask",
@@ -61,6 +67,142 @@ static void verify_success(const char *prog_name)
 	cpumask_success__destroy(skel);
 }
 
+static const char * const cpumask_iter_success_testcases[] = {
+	"test_cpumask_iter",
+	"test_cpumask_iter_sleepable",
+};
+
+static int read_percpu_data(struct bpf_link *link, int nr_cpu_exp, int nr_running_exp)
+{
+	int iter_fd, len, item, nr_running, psi_running, nr_cpus, err = -1;
+	char buf[128];
+	size_t left;
+	char *p;
+
+	iter_fd = bpf_iter_create(bpf_link__fd(link));
+	if (!ASSERT_GE(iter_fd, 0, "iter_fd"))
+		return -1;
+
+	memset(buf, 0, sizeof(buf));
+	left = ARRAY_SIZE(buf);
+	p = buf;
+	while ((len = read(iter_fd, p, left)) > 0) {
+		p += len;
+		left -= len;
+	}
+
+	item = sscanf(buf, "nr_running %u nr_cpus %u psi_running %u\n",
+		      &nr_running, &nr_cpus, &psi_running);
+	if (!ASSERT_EQ(item, 3, "seq_format"))
+		goto out;
+	if (!ASSERT_EQ(nr_cpus, nr_cpu_exp, "nr_cpus"))
+		goto out;
+	if (!ASSERT_GE(nr_running, nr_running_exp, "nr_running"))
+		goto out;
+	if (!ASSERT_GE(psi_running, nr_running_exp, "psi_running"))
+		goto out;
+
+	err = 0;
+out:
+	close(iter_fd);
+	return err;
+}
+
+static void verify_iter_success(const char *prog_name)
+{
+	DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
+	int cgrp_fd, nr_cpus, err, i, chosen = 0;
+	struct cpumask_iter_success *skel;
+	union bpf_iter_link_info linfo;
+	struct bpf_program *prog;
+	struct bpf_link *link;
+	cpu_set_t set;
+
+	if (setup_cgroup_environment())
+		return;
+
+	/* Utilize the cgroup iter */
+	cgrp_fd = get_root_cgroup();
+	if (!ASSERT_GE(cgrp_fd, 0, "create_cgrp"))
+		goto cleanup;
+
+	skel = cpumask_iter_success__open();
+	if (!ASSERT_OK_PTR(skel, "cpumask_iter_success__open"))
+		goto close_fd;
+
+	skel->bss->pid = getpid();
+	nr_cpus = libbpf_num_possible_cpus();
+
+	err = cpumask_iter_success__load(skel);
+	if (!ASSERT_OK(err, "cpumask_iter_success__load"))
+		goto destroy;
+
+	prog = bpf_object__find_program_by_name(skel->obj, prog_name);
+	if (!ASSERT_OK_PTR(prog, "bpf_object__find_program_by_name"))
+		goto destroy;
+
+	memset(&linfo, 0, sizeof(linfo));
+	linfo.cgroup.cgroup_fd = cgrp_fd;
+	linfo.cgroup.order = BPF_CGROUP_ITER_SELF_ONLY;
+	opts.link_info = &linfo;
+	opts.link_info_len = sizeof(linfo);
+	link = bpf_program__attach_iter(prog, &opts);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach"))
+		goto destroy;
+
+	/* Case 1): Enable all possible CPUs */
+	CPU_ZERO(&set);
+	for (i = 0; i < nr_cpus; i++)
+		CPU_SET(i, &set);
+	err = sched_setaffinity(skel->bss->pid, sizeof(set), &set);
+	if (!ASSERT_OK(err, "setaffinity_all_cpus"))
+		goto free_link;
+	err = read_percpu_data(link, nr_cpus, 1);
+	if (!ASSERT_OK(err, "read_percpu_data"))
+		goto free_link;
+	if (!ASSERT_OK(skel->bss->err, "null_rq"))
+		goto free_link;
+
+	/* Case 2): CPU0 only */
+	CPU_ZERO(&set);
+	CPU_SET(0, &set);
+	err = sched_setaffinity(skel->bss->pid, sizeof(set), &set);
+	if (!ASSERT_OK(err, "setaffinity_cpu0"))
+		goto free_link;
+	err = read_percpu_data(link, 1, 1);
+	if (!ASSERT_OK(err, "read_percpu_data"))
+		goto free_link;
+	if (!ASSERT_OK(skel->bss->err, "null_rq_psi"))
+		goto free_link;
+
+	/* Case 3): Partial CPUs */
+	CPU_ZERO(&set);
+	for (i = 0; i < nr_cpus; i++) {
+		if (i < 4 && i & 0x1)
+			continue;
+		if (i > 8 && i & 0x2)
+			continue;
+		CPU_SET(i, &set);
+		chosen++;
+	}
+	err = sched_setaffinity(skel->bss->pid, sizeof(set), &set);
+	if (!ASSERT_OK(err, "setaffinity_partial_cpus"))
+		goto free_link;
+	err = read_percpu_data(link, chosen, 1);
+	if (!ASSERT_OK(err, "read_percpu_data"))
+		goto free_link;
+	ASSERT_OK(skel->bss->err, "null_rq_psi");
+
+free_link:
+	bpf_link__destroy(link);
+destroy:
+	cpumask_iter_success__destroy(skel);
+close_fd:
+	close(cgrp_fd);
+cleanup:
+	cleanup_cgroup_environment();
+}
+
 void test_cpumask(void)
 {
 	int i;
@@ -74,4 +216,14 @@ void test_cpumask(void)
 
 	RUN_TESTS(cpumask_success);
 	RUN_TESTS(cpumask_failure);
+
+	for (i = 0; i < ARRAY_SIZE(cpumask_iter_success_testcases); i++) {
+		if (!test__start_subtest(cpumask_iter_success_testcases[i]))
+			continue;
+
+		verify_iter_success(cpumask_iter_success_testcases[i]);
+	}
+
+	RUN_TESTS(cpumask_iter_success);
+	RUN_TESTS(cpumask_iter_failure);
 }
diff --git a/tools/testing/selftests/bpf/progs/cpumask_common.h b/tools/testing/selftests/bpf/progs/cpumask_common.h
index c705d8112a35..fb65943ef130 100644
--- a/tools/testing/selftests/bpf/progs/cpumask_common.h
+++ b/tools/testing/selftests/bpf/progs/cpumask_common.h
@@ -56,6 +56,9 @@ u32 bpf_cpumask_any_distribute(const struct cpumask *src) __ksym __weak;
 u32 bpf_cpumask_any_and_distribute(const struct cpumask *src1,
 				   const struct cpumask *src2) __ksym __weak;
 u32 bpf_cpumask_weight(const struct cpumask *cpumask) __ksym __weak;
+int bpf_iter_cpumask_new(struct bpf_iter_cpumask *it, const struct cpumask *mask) __ksym __weak;
+int *bpf_iter_cpumask_next(struct bpf_iter_cpumask *it) __ksym __weak;
+void bpf_iter_cpumask_destroy(struct bpf_iter_cpumask *it) __ksym __weak;
 
 void bpf_rcu_read_lock(void) __ksym __weak;
 void bpf_rcu_read_unlock(void) __ksym __weak;
diff --git a/tools/testing/selftests/bpf/progs/cpumask_iter_failure.c b/tools/testing/selftests/bpf/progs/cpumask_iter_failure.c
new file mode 100644
index 000000000000..3d304cee0a72
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/cpumask_iter_failure.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2024 Yafang Shao <laoar.shao@gmail.com> */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#include "bpf_misc.h"
+#include "task_kfunc_common.h"
+#include "cpumask_common.h"
+
+char _license[] SEC("license") = "GPL";
+
+SEC("iter.s/cgroup")
+__failure __msg("R2 must be a rcu pointer")
+int BPF_PROG(test_cpumask_iter_no_rcu, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+{
+	struct task_struct *p;
+	int *cpu;
+
+	p = bpf_task_from_pid(1);
+	if (!p)
+		return 1;
+
+	bpf_for_each(cpumask, cpu, p->cpus_ptr) {
+	}
+	bpf_task_release(p);
+	return 0;
+}
+
+SEC("iter/cgroup")
+__failure __msg("Possibly NULL pointer passed to trusted arg1")
+int BPF_PROG(test_cpumask_iter_null_pointer, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+{
+	struct cpumask *mask = NULL;
+	int *cpu;
+
+	bpf_for_each(cpumask, cpu, mask) {
+	}
+	return 0;
+}
+
+SEC("iter.s/cgroup")
+__failure __msg("Unreleased reference id=3 alloc_insn=10")
+int BPF_PROG(test_cpumask_iter_no_destroy, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+{
+	struct bpf_iter_cpumask it;
+	struct task_struct *p;
+
+	p = bpf_task_from_pid(1);
+	if (!p)
+		return 1;
+
+	bpf_rcu_read_lock();
+	bpf_iter_cpumask_new(&it, p->cpus_ptr);
+	bpf_rcu_read_unlock();
+
+	bpf_iter_cpumask_next(&it);
+	bpf_task_release(p);
+	return 0;
+}
+
+SEC("iter/cgroup")
+__failure __msg("expected an initialized iter_cpumask as arg #1")
+int BPF_PROG(test_cpumask_iter_next_uninit, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+{
+	struct bpf_iter_cpumask *it = NULL;
+
+	bpf_iter_cpumask_next(it);
+	return 0;
+}
+
+SEC("iter/cgroup")
+__failure __msg("expected an initialized iter_cpumask as arg #1")
+int BPF_PROG(test_cpumask_iter_next_uninit2, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+{
+	struct bpf_iter_cpumask it = {};
+
+	bpf_iter_cpumask_next(&it);
+	return 0;
+}
+
+SEC("iter/cgroup")
+__failure __msg("expected an initialized iter_cpumask as arg #1")
+int BPF_PROG(test_cpumask_iter_destroy_uninit, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+{
+	struct bpf_iter_cpumask_kern it = {.cpu = -1};
+	struct bpf_cpumask *mask;
+
+	mask = bpf_cpumask_create();
+	if (!mask)
+		return 1;
+
+	bpf_cpumask_setall(mask);
+	it.mask = &mask->cpumask;
+	bpf_iter_cpumask_destroy((struct bpf_iter_cpumask *)&it);
+	bpf_cpumask_release(mask);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/cpumask_iter_success.c b/tools/testing/selftests/bpf/progs/cpumask_iter_success.c
new file mode 100644
index 000000000000..a71db42cc38a
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/cpumask_iter_success.c
@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2024 Yafang Shao <laoar.shao@gmail.com> */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#include "task_kfunc_common.h"
+#include "cpumask_common.h"
+
+char _license[] SEC("license") = "GPL";
+
+extern const struct psi_group_cpu system_group_pcpu __ksym __weak;
+extern const struct rq runqueues __ksym __weak;
+
+int pid;
+
+static void read_percpu_data(struct bpf_iter_meta *meta, struct cgroup *cgrp, const cpumask_t *mask)
+{
+	u32 nr_running = 0, psi_nr_running = 0, nr_cpus = 0;
+	struct psi_group_cpu *groupc;
+	struct rq *rq;
+	int *cpu;
+
+	bpf_for_each(cpumask, cpu, mask) {
+		rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, *cpu);
+		if (!rq) {
+			err += 1;
+			continue;
+		}
+		nr_running += rq->nr_running;
+		nr_cpus += 1;
+
+		groupc = (struct psi_group_cpu *)bpf_per_cpu_ptr(&system_group_pcpu, *cpu);
+		if (!groupc) {
+			err += 1;
+			continue;
+		}
+		psi_nr_running += groupc->tasks[NR_RUNNING];
+	}
+	BPF_SEQ_PRINTF(meta->seq, "nr_running %u nr_cpus %u psi_running %u\n",
+		       nr_running, nr_cpus, psi_nr_running);
+}
+
+SEC("iter.s/cgroup")
+int BPF_PROG(test_cpumask_iter_sleepable, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+{
+	struct task_struct *p;
+
+	/* epilogue */
+	if (!cgrp)
+		return 0;
+
+	bpf_rcu_read_lock();
+	p = bpf_task_from_pid(pid);
+	if (!p) {
+		bpf_rcu_read_unlock();
+		return 1;
+	}
+
+	read_percpu_data(meta, cgrp, p->cpus_ptr);
+	bpf_task_release(p);
+	bpf_rcu_read_unlock();
+	return 0;
+}
+
+SEC("iter/cgroup")
+int BPF_PROG(test_cpumask_iter, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+{
+	struct task_struct *p;
+
+	/* epilogue */
+	if (!cgrp)
+		return 0;
+
+	p = bpf_task_from_pid(pid);
+	if (!p)
+		return 1;
+
+	read_percpu_data(meta, cgrp, p->cpus_ptr);
+	bpf_task_release(p);
+	return 0;
+}
+
+SEC("iter.s/cgroup")
+int BPF_PROG(test_cpumask_iter_next_no_rcu, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+{
+	struct bpf_iter_cpumask it;
+	struct task_struct *p;
+
+	p = bpf_task_from_pid(1);
+	if (!p)
+		return 1;
+
+	/* RCU is only required by bpf_iter_cpumask_new(). */
+	bpf_rcu_read_lock();
+	bpf_iter_cpumask_new(&it, p->cpus_ptr);
+	bpf_rcu_read_unlock();
+
+	bpf_iter_cpumask_next(&it);
+	bpf_iter_cpumask_destroy(&it);
+
+	bpf_task_release(p);
+	return 0;
+}
+
+SEC("iter.s/cgroup")
+int BPF_PROG(test_cpumask_iter_no_next, struct bpf_iter_meta *meta, struct cgroup *cgrp)
+{
+	struct bpf_iter_cpumask it;
+	struct task_struct *p;
+
+	p = bpf_task_from_pid(1);
+	if (!p)
+		return 1;
+
+	bpf_rcu_read_lock();
+	bpf_iter_cpumask_new(&it, p->cpus_ptr);
+	bpf_rcu_read_unlock();
+
+	/* It is fine without calling bpf_iter_cpumask_next(). */
+
+	bpf_iter_cpumask_destroy(&it);
+	bpf_task_release(p);
+	return 0;
+}
-- 
2.39.1

Re: [PATCH v6 bpf-next 4/5] selftests/bpf: Mark cpumask kfunc declarations as __weak

[Daniel Xu]

On Tue, Feb 06, 2024 at 04:14:15PM +0800, Yafang Shao wrote:
> After the series "Annotate kfuncs in .BTF_ids section"[0], kfuncs can be
> generated from bpftool. Let's mark the existing cpumask kfunc declarations
> __weak so they don't conflict with definitions that will eventually come
> from vmlinux.h.
> 
> [0]. https://lore.kernel.org/all/cover.1706491398.git.dxu@dxuuu.xyz
> 
> Suggested-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Cc: Daniel Xu <dxu@dxuuu.xyz>
> ---
>  .../selftests/bpf/progs/cpumask_common.h      | 57 ++++++++++---------
>  1 file changed, 29 insertions(+), 28 deletions(-)

Thanks!

Acked-by: Daniel Xu <dxu@dxuuu.xyz>

[..]

Re: [PATCH v6 bpf-next 1/5] bpf: Add bpf_iter_cpumask kfuncs

[Alexei Starovoitov]

On Tue, Feb 6, 2024 at 12:14 AM Yafang Shao <laoar.shao@gmail.com> wrote:
>
> Add three new kfuncs for bpf_iter_cpumask.
> - bpf_iter_cpumask_new
>   KF_RCU is defined because the cpumask must be a RCU trusted pointer
>   such as task->cpus_ptr.
> - bpf_iter_cpumask_next
> - bpf_iter_cpumask_destroy
>
> These new kfuncs facilitate the iteration of percpu data, such as
> runqueues, psi_cgroup_cpu, and more.
>
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> ---
>  kernel/bpf/cpumask.c | 79 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
>
> diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
> index dad0fb1c8e87..ed6078cfa40e 100644
> --- a/kernel/bpf/cpumask.c
> +++ b/kernel/bpf/cpumask.c
> @@ -422,6 +422,82 @@ __bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask)
>         return cpumask_weight(cpumask);
>  }
>
> +struct bpf_iter_cpumask {
> +       __u64 __opaque[2];
> +} __aligned(8);
> +
> +struct bpf_iter_cpumask_kern {
> +       struct cpumask *mask;
> +       int cpu;
> +} __aligned(8);
> +
> +/**
> + * bpf_iter_cpumask_new() - Initialize a new CPU mask iterator for a given CPU mask
> + * @it: The new bpf_iter_cpumask to be created.
> + * @mask: The cpumask to be iterated over.
> + *
> + * This function initializes a new bpf_iter_cpumask structure for iterating over
> + * the specified CPU mask. It assigns the provided cpumask to the newly created
> + * bpf_iter_cpumask @it for subsequent iteration operations.
> + *
> + * On success, 0 is returned. On failure, ERR is returned.
> + */
> +__bpf_kfunc int bpf_iter_cpumask_new(struct bpf_iter_cpumask *it, const struct cpumask *mask)
> +{
> +       struct bpf_iter_cpumask_kern *kit = (void *)it;
> +
> +       BUILD_BUG_ON(sizeof(struct bpf_iter_cpumask_kern) > sizeof(struct bpf_iter_cpumask));
> +       BUILD_BUG_ON(__alignof__(struct bpf_iter_cpumask_kern) !=
> +                    __alignof__(struct bpf_iter_cpumask));
> +
> +       kit->mask = bpf_mem_alloc(&bpf_global_ma, cpumask_size());
> +       if (!kit->mask)
> +               return -ENOMEM;
> +
> +       cpumask_copy(kit->mask, mask);

Since it's mem_alloc plus memcpy how about we make it more
generic ?
Instead of cpumask specific let's pass arbitrary
"void *unsafe_addr, u32 size"

allocate that much and probe_read_kernel into the buffer?


> +__bpf_kfunc int *bpf_iter_cpumask_next(struct bpf_iter_cpumask *it)
> +{
> +       struct bpf_iter_cpumask_kern *kit = (void *)it;
> +       const struct cpumask *mask = kit->mask;
> +       int cpu;
> +
> +       if (!mask)
> +               return NULL;
> +       cpu = cpumask_next(kit->cpu, mask);

Instead of cpumask_next() call find_next_bit()

> +       if (cpu >= nr_cpu_ids)
> +               return NULL;

instead of nr_cpu_ids we can check size in bits of copied bit array.

> BTF_ID_FLAGS(func, bpf_iter_cpumask_new, KF_ITER_NEW | KF_RCU)

KF_RCU is also not needed.
Such iterator will be callable from anywhere and on any address.

wdyt?

Re: [PATCH v6 bpf-next 1/5] bpf: Add bpf_iter_cpumask kfuncs

[Yafang Shao]

On Wed, Feb 7, 2024 at 9:06 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Tue, Feb 6, 2024 at 12:14 AM Yafang Shao <laoar.shao@gmail.com> wrote:
> >
> > Add three new kfuncs for bpf_iter_cpumask.
> > - bpf_iter_cpumask_new
> >   KF_RCU is defined because the cpumask must be a RCU trusted pointer
> >   such as task->cpus_ptr.
> > - bpf_iter_cpumask_next
> > - bpf_iter_cpumask_destroy
> >
> > These new kfuncs facilitate the iteration of percpu data, such as
> > runqueues, psi_cgroup_cpu, and more.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  kernel/bpf/cpumask.c | 79 ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 79 insertions(+)
> >
> > diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
> > index dad0fb1c8e87..ed6078cfa40e 100644
> > --- a/kernel/bpf/cpumask.c
> > +++ b/kernel/bpf/cpumask.c
> > @@ -422,6 +422,82 @@ __bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask)
> >         return cpumask_weight(cpumask);
> >  }
> >
> > +struct bpf_iter_cpumask {
> > +       __u64 __opaque[2];
> > +} __aligned(8);
> > +
> > +struct bpf_iter_cpumask_kern {
> > +       struct cpumask *mask;
> > +       int cpu;
> > +} __aligned(8);
> > +
> > +/**
> > + * bpf_iter_cpumask_new() - Initialize a new CPU mask iterator for a given CPU mask
> > + * @it: The new bpf_iter_cpumask to be created.
> > + * @mask: The cpumask to be iterated over.
> > + *
> > + * This function initializes a new bpf_iter_cpumask structure for iterating over
> > + * the specified CPU mask. It assigns the provided cpumask to the newly created
> > + * bpf_iter_cpumask @it for subsequent iteration operations.
> > + *
> > + * On success, 0 is returned. On failure, ERR is returned.
> > + */
> > +__bpf_kfunc int bpf_iter_cpumask_new(struct bpf_iter_cpumask *it, const struct cpumask *mask)
> > +{
> > +       struct bpf_iter_cpumask_kern *kit = (void *)it;
> > +
> > +       BUILD_BUG_ON(sizeof(struct bpf_iter_cpumask_kern) > sizeof(struct bpf_iter_cpumask));
> > +       BUILD_BUG_ON(__alignof__(struct bpf_iter_cpumask_kern) !=
> > +                    __alignof__(struct bpf_iter_cpumask));
> > +
> > +       kit->mask = bpf_mem_alloc(&bpf_global_ma, cpumask_size());
> > +       if (!kit->mask)
> > +               return -ENOMEM;
> > +
> > +       cpumask_copy(kit->mask, mask);
>
> Since it's mem_alloc plus memcpy how about we make it more
> generic ?
> Instead of cpumask specific let's pass arbitrary
> "void *unsafe_addr, u32 size"
>
> allocate that much and probe_read_kernel into the buffer?
>
>
> > +__bpf_kfunc int *bpf_iter_cpumask_next(struct bpf_iter_cpumask *it)
> > +{
> > +       struct bpf_iter_cpumask_kern *kit = (void *)it;
> > +       const struct cpumask *mask = kit->mask;
> > +       int cpu;
> > +
> > +       if (!mask)
> > +               return NULL;
> > +       cpu = cpumask_next(kit->cpu, mask);
>
> Instead of cpumask_next() call find_next_bit()
>
> > +       if (cpu >= nr_cpu_ids)
> > +               return NULL;
>
> instead of nr_cpu_ids we can check size in bits of copied bit array.
>
> > BTF_ID_FLAGS(func, bpf_iter_cpumask_new, KF_ITER_NEW | KF_RCU)
>
> KF_RCU is also not needed.
> Such iterator will be callable from anywhere and on any address.
>
> wdyt?

Good suggestion. A more generic bitmap iter is better. I will analyze it.

-- 
Regards
Yafang

Re: [PATCH v6 bpf-next 0/5] bpf: Add bpf_iter_cpumask

[Andrii Nakryiko]

On Tue, Feb 6, 2024 at 12:14 AM Yafang Shao <laoar.shao@gmail.com> wrote:
>
> Three new kfuncs, namely bpf_iter_cpumask_{new,next,destroy}, have been
> added for the new bpf_iter_cpumask functionality. These kfuncs enable the
> iteration of percpu data, such as runqueues, system_group_pcpu, and more.
>
> In our specific use case, we leverage the cgroup iterator to traverse
> percpu data, subsequently exposing it to userspace through a seq file.
> Refer to example in patch #2 for the usage.
>
> Changes:
> - v5 -> v6:
>   - Various improvements on the comments (Andrii)
>   - Use a static function instead as Kumar's patch[0] has been merged.
>     (Anrii, Yonghong)
>
> [0]. https://lore.kernel.org/bpf/170719262630.31872.2248639771567354367.git-patchwork-notify@kernel.org
>
> - v4 -> v5:
>   - Use cpumask_size() instead of sizeof(struct cpumask) (David)
>   - Refactor the selftests as suggsted by David
>   - Improve the doc as suggested by David
> - v3 -> v4:
>   - Use a copy of cpumask to avoid potential use-after-free (Yonghong)
>   - Various code improvement in selftests (Yonghong)
> - v2 -> v3:
>   - Define KF_RCU_PROTECTED for bpf_iter_cpumask_new (Alexei)
>   - Code improvement in selftests
>   - Fix build error in selftest due to CONFIG_PSI=n
>     reported by kernel test robot <lkp@intel.com>
> - v1 -> v2:
>   - Avoid changing cgroup subsystem (Tejun)
>   - Remove bpf_cpumask_set_from_pid(), and use bpf_cpumask_copy()
>     instead (Tejun)
>   - Use `int cpu;` field in bpf_iter_cpumask_kern (Andrii)
>
> Yafang Shao (5):
>   bpf: Add bpf_iter_cpumask kfuncs
>   bpf, docs: Add document for cpumask iter
>   selftests/bpf: Fix error checking for cpumask_success__load()
>   selftests/bpf: Mark cpumask kfunc declarations as __weak

I've applied patches 3 and 4, as they are general clean ups and
improvements independent from the actual iterator implementation.
Thanks!

>   selftests/bpf: Add selftests for cpumask iter
>
>  Documentation/bpf/cpumasks.rst                |  60 +++++++
>  kernel/bpf/cpumask.c                          |  79 +++++++++
>  tools/testing/selftests/bpf/config            |   1 +
>  .../selftests/bpf/prog_tests/cpumask.c        | 158 +++++++++++++++++-
>  .../selftests/bpf/progs/cpumask_common.h      |  60 +++----
>  .../bpf/progs/cpumask_iter_failure.c          |  99 +++++++++++
>  .../bpf/progs/cpumask_iter_success.c          | 126 ++++++++++++++
>  7 files changed, 552 insertions(+), 31 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_failure.c
>  create mode 100644 tools/testing/selftests/bpf/progs/cpumask_iter_success.c
>
> --
> 2.39.1
>