[RFC PATCH 21/30] lib: implement context capture support for page and slab allocators

Suren Baghdasaryan
2022-08-30T21:53:15Z

Implement mechanisms for capturing allocation call context which consists
of:
- allocation size
- pid, tgid and name of the allocating task
- allocation timestamp
- allocation call stack
The patch creates alloc_tags.ctx file which can be written to
enable/disable context capture for a specific code tag. Captured context
can be obtained by reading alloc_tags.ctx file.
Usage example:

echo "file include/asm-generic/pgalloc.h line 63 enable" > \
/sys/kernel/debug/alloc_tags.ctx
cat alloc_tags.ctx
91.0MiB 212 include/asm-generic/pgalloc.h:63 module:pgtable func:__pte_alloc_one
size: 4096
pid: 1551
tgid: 1551
comm: cat
ts: 670109646361
call stack:
pte_alloc_one+0xfe/0x130
__pte_alloc+0x22/0x90
move_page_tables.part.0+0x994/0xa60
shift_arg_pages+0xa4/0x180
setup_arg_pages+0x286/0x2d0
load_elf_binary+0x4e1/0x18d0
bprm_execve+0x26b/0x660
do_execveat_common.isra.0+0x19d/0x220
__x64_sys_execve+0x2e/0x40
do_syscall_64+0x38/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd

size: 4096
pid: 1551
tgid: 1551
comm: cat
ts: 670109711801
call stack:
pte_alloc_one+0xfe/0x130
__do_fault+0x52/0xc0
__handle_mm_fault+0x7d9/0xdd0
handle_mm_fault+0xc0/0x2b0
do_user_addr_fault+0x1c3/0x660
exc_page_fault+0x62/0x150
asm_exc_page_fault+0x22/0x30
...

echo "file include/asm-generic/pgalloc.h line 63 disable" > \
/sys/kernel/debug/alloc_tags.ctx

Note that disabling context capture will not clear already captured
context but no new context will be captured.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/alloc_tag.h | 28 ++++-
include/linux/codetag.h | 3 +-
lib/Kconfig.debug | 1 +
lib/alloc_tag.c | 239 +++++++++++++++++++++++++++++++++++++-
lib/codetag.c | 20 ++--
5 files changed, 273 insertions(+), 18 deletions(-)

diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
index b3f589afb1c9..66638cbf349a 100644
--- a/include/linux/alloc_tag.h
+++ b/include/linux/alloc_tag.h
@@ -16,27 +16,41 @@
* an array of these. Embedded codetag utilizes codetag framework.
*/
struct alloc_tag {
- struct codetag ct;
+ struct codetag_with_ctx ctc;
unsigned long last_wrap;
struct raw_lazy_percpu_counter call_count;
struct raw_lazy_percpu_counter bytes_allocated;
} __aligned(8);

+static inline struct alloc_tag *ctc_to_alloc_tag(struct codetag_with_ctx *ctc)
+{
+ return container_of(ctc, struct alloc_tag, ctc);
+}
+
static inline struct alloc_tag *ct_to_alloc_tag(struct codetag *ct)
{
- return container_of(ct, struct alloc_tag, ct);
+ return container_of(ct_to_ctc(ct), struct alloc_tag, ctc);
}

+struct codetag_ctx *alloc_tag_create_ctx(struct alloc_tag *tag, size_t size);
+void alloc_tag_free_ctx(struct codetag_ctx *ctx, struct alloc_tag **ptag);
+bool alloc_tag_enable_ctx(struct alloc_tag *tag, bool enable);
+
#define DEFINE_ALLOC_TAG(_alloc_tag) \
static struct alloc_tag _alloc_tag __used __aligned(8) \
- __section("alloc_tags") = { .ct = CODE_TAG_INIT }
+ __section("alloc_tags") = { .ctc.ct = CODE_TAG_INIT }

#define alloc_tag_counter_read(counter) \
__lazy_percpu_counter_read(counter)

static inline void __alloc_tag_sub(union codetag_ref *ref, size_t bytes)
{
- struct alloc_tag *tag = ct_to_alloc_tag(ref->ct);
+ struct alloc_tag *tag;
+
+ if (is_codetag_ctx_ref(ref))
+ alloc_tag_free_ctx(ref->ctx, &tag);
+ else
+ tag = ct_to_alloc_tag(ref->ct);

__lazy_percpu_counter_add(&tag->call_count, &tag->last_wrap, -1);
__lazy_percpu_counter_add(&tag->bytes_allocated, &tag->last_wrap, -bytes);
@@ -51,7 +65,11 @@ do { \

static inline void __alloc_tag_add(struct alloc_tag *tag, union codetag_ref *ref, size_t bytes)
{
- ref->ct = &tag->ct;
+ if (codetag_ctx_enabled(&tag->ctc))
+ ref->ctx = alloc_tag_create_ctx(tag, bytes);
+ else
+ ref->ct = &tag->ctc.ct;
+
__lazy_percpu_counter_add(&tag->call_count, &tag->last_wrap, 1);
__lazy_percpu_counter_add(&tag->bytes_allocated, &tag->last_wrap, bytes);
}
diff --git a/include/linux/codetag.h b/include/linux/codetag.h
index 57736ec77b45..a10c5fcbdd20 100644
--- a/include/linux/codetag.h
+++ b/include/linux/codetag.h
@@ -104,7 +104,8 @@ struct codetag_with_ctx *ct_to_ctc(struct codetag *ct)
}

void codetag_lock_module_list(struct codetag_type *cttype, bool lock);
-struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype);
+void codetag_init_iter(struct codetag_iterator *iter,
+ struct codetag_type *cttype);
struct codetag *codetag_next_ct(struct codetag_iterator *iter);
struct codetag_ctx *codetag_next_ctx(struct codetag_iterator *iter);

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 08c97a978906..2790848464f1 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -977,6 +977,7 @@ config ALLOC_TAGGING
bool
select CODE_TAGGING
select LAZY_PERCPU_COUNTER
+ select STACKDEPOT

config PAGE_ALLOC_TAGGING
bool "Enable page allocation tagging"
diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index 082fbde184ef..50d7bdc2a3c8 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -1,12 +1,75 @@
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/alloc_tag.h>
+#include <linux/codetag_ctx.h>
#include <linux/debugfs.h>
#include <linux/fs.h>
#include <linux/gfp.h>
#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/sched/clock.h>
#include <linux/seq_buf.h>
+#include <linux/stackdepot.h>
#include <linux/uaccess.h>

+#define STACK_BUF_SIZE 1024
+
+struct alloc_call_ctx {
+ struct codetag_ctx ctx;
+ size_t size;
+ pid_t pid;
+ pid_t tgid;
+ char comm[TASK_COMM_LEN];
+ u64 ts_nsec;
+ depot_stack_handle_t stack_handle;
+} __aligned(8);
+
+static void alloc_tag_ops_free_ctx(struct kref *refcount)
+{
+ kfree(container_of(kref_to_ctx(refcount), struct alloc_call_ctx, ctx));
+}
+
+struct codetag_ctx *alloc_tag_create_ctx(struct alloc_tag *tag, size_t size)
+{
+ struct alloc_call_ctx *ac_ctx;
+
+ /* TODO: use a dedicated kmem_cache */
+ ac_ctx = kmalloc(sizeof(struct alloc_call_ctx), GFP_KERNEL);
+ if (WARN_ON(!ac_ctx))
+ return NULL;
+
+ ac_ctx->size = size;
+ ac_ctx->pid = current->pid;
+ ac_ctx->tgid = current->tgid;
+ strscpy(ac_ctx->comm, current->comm, sizeof(ac_ctx->comm));
+ ac_ctx->ts_nsec = local_clock();
+ ac_ctx->stack_handle =
+ stack_depot_capture_stack(GFP_NOWAIT | __GFP_NOWARN);
+ add_ctx(&ac_ctx->ctx, &tag->ctc);
+
+ return &ac_ctx->ctx;
+}
+EXPORT_SYMBOL_GPL(alloc_tag_create_ctx);
+
+void alloc_tag_free_ctx(struct codetag_ctx *ctx, struct alloc_tag **ptag)
+{
+ *ptag = ctc_to_alloc_tag(ctx->ctc);
+ rem_ctx(ctx, alloc_tag_ops_free_ctx);
+}
+EXPORT_SYMBOL_GPL(alloc_tag_free_ctx);
+
+bool alloc_tag_enable_ctx(struct alloc_tag *tag, bool enable)
+{
+ static bool stack_depot_ready;
+
+ if (enable && !stack_depot_ready) {
+ stack_depot_init();
+ stack_depot_capture_init();
+ stack_depot_ready = true;
+ }
+
+ return codetag_enable_ctx(&tag->ctc, enable);
+}
+
#ifdef CONFIG_DEBUG_FS

struct alloc_tag_file_iterator {
@@ -50,7 +113,7 @@ static int alloc_tag_file_open(struct inode *inode, struct file *file)
return -ENOMEM;

codetag_lock_module_list(cttype, true);
- iter->ct_iter = codetag_get_ct_iter(cttype);
+ codetag_init_iter(&iter->ct_iter, cttype);
codetag_lock_module_list(cttype, false);
seq_buf_init(&iter->buf, iter->rawbuf, sizeof(iter->rawbuf));
file->private_data = iter;
@@ -111,14 +174,182 @@ static const struct file_operations alloc_tag_file_ops = {
.read = alloc_tag_file_read,
};

+static void alloc_tag_ctx_to_text(struct seq_buf *out, struct codetag_ctx *ctx)
+{
+ struct alloc_call_ctx *ac_ctx;
+ char *buf;
+
+ ac_ctx = container_of(ctx, struct alloc_call_ctx, ctx);
+ seq_buf_printf(out, " size: %zu\n", ac_ctx->size);
+ seq_buf_printf(out, " pid: %d\n", ac_ctx->pid);
+ seq_buf_printf(out, " tgid: %d\n", ac_ctx->tgid);
+ seq_buf_printf(out, " comm: %s\n", ac_ctx->comm);
+ seq_buf_printf(out, " ts: %llu\n", ac_ctx->ts_nsec);
+
+ buf = kmalloc(STACK_BUF_SIZE, GFP_KERNEL);
+ if (buf) {
+ int bytes_read = stack_depot_snprint(ac_ctx->stack_handle, buf,
+ STACK_BUF_SIZE - 1, 8);
+ buf[bytes_read] = '\0';
+ seq_buf_printf(out, " call stack:\n%s\n", buf);
+ }
+ kfree(buf);
+}
+
+static ssize_t alloc_tag_ctx_file_read(struct file *file, char __user *ubuf,
+ size_t size, loff_t *ppos)
+{
+ struct alloc_tag_file_iterator *iter = file->private_data;
+ struct codetag_iterator *ct_iter = &iter->ct_iter;
+ struct user_buf buf = { .buf = ubuf, .size = size };
+ struct codetag_ctx *ctx;
+ struct codetag *prev_ct;
+ int err = 0;
+
+ codetag_lock_module_list(ct_iter->cttype, true);
+ while (1) {
+ err = flush_ubuf(&buf, &iter->buf);
+ if (err || !buf.size)
+ break;
+
+ prev_ct = ct_iter->ct;
+ ctx = codetag_next_ctx(ct_iter);
+ if (!ctx)
+ break;
+
+ if (prev_ct != &ctx->ctc->ct)
+ alloc_tag_to_text(&iter->buf, &ctx->ctc->ct);
+ alloc_tag_ctx_to_text(&iter->buf, ctx);
+ }
+ codetag_lock_module_list(ct_iter->cttype, false);
+
+ return err ? : buf.ret;
+}
+
+#define CTX_CAPTURE_TOKENS() \
+ x(disable, 0) \
+ x(enable, 0)
+
+static const char * const ctx_capture_token_strs[] = {
+#define x(name, nr_args) #name,
+ CTX_CAPTURE_TOKENS()
+#undef x
+ NULL
+};
+
+enum ctx_capture_token {
+#define x(name, nr_args) TOK_##name,
+ CTX_CAPTURE_TOKENS()
+#undef x
+};
+
+static int enable_ctx_capture(struct codetag_type *cttype,
+ struct codetag_query *query, bool enable)
+{
+ struct codetag_iterator ct_iter;
+ struct codetag_with_ctx *ctc;
+ struct codetag *ct;
+ unsigned int nfound = 0;
+
+ codetag_lock_module_list(cttype, true);
+
+ codetag_init_iter(&ct_iter, cttype);
+ while ((ct = codetag_next_ct(&ct_iter))) {
+ if (!codetag_matches_query(query, ct, ct_iter.cmod, NULL))
+ continue;
+
+ ctc = ct_to_ctc(ct);
+ if (codetag_ctx_enabled(ctc) == enable)
+ continue;
+
+ if (!alloc_tag_enable_ctx(ctc_to_alloc_tag(ctc), enable)) {
+ pr_warn("Failed to toggle context capture\n");
+ continue;
+ }
+
+ nfound++;
+ }
+
+ codetag_lock_module_list(cttype, false);
+
+ return nfound ? 0 : -ENOENT;
+}
+
+static int parse_command(struct codetag_type *cttype, char *buf)
+{
+ struct codetag_query query = { NULL };
+ char *cmd;
+ int ret;
+ int tok;
+
+ buf = codetag_query_parse(&query, buf);
+ if (IS_ERR(buf))
+ return PTR_ERR(buf);
+
+ cmd = strsep_no_empty(&buf, " \t\r\n");
+ if (!cmd)
+ return -EINVAL; /* no command */
+
+ tok = match_string(ctx_capture_token_strs,
+ ARRAY_SIZE(ctx_capture_token_strs), cmd);
+ if (tok < 0)
+ return -EINVAL; /* unknown command */
+
+ ret = enable_ctx_capture(cttype, &query, tok == TOK_enable);
+ if (ret < 0)
+ return ret;
+
+ return 0;
+}
+
+static ssize_t alloc_tag_ctx_file_write(struct file *file, const char __user *ubuf,
+ size_t len, loff_t *offp)
+{
+ struct alloc_tag_file_iterator *iter = file->private_data;
+ char tmpbuf[256];
+
+ if (len == 0)
+ return 0;
+ /* we don't check *offp -- multiple writes() are allowed */
+ if (len > sizeof(tmpbuf) - 1)
+ return -E2BIG;
+
+ if (copy_from_user(tmpbuf, ubuf, len))
+ return -EFAULT;
+
+ tmpbuf[len] = '\0';
+ parse_command(iter->ct_iter.cttype, tmpbuf);
+
+ *offp += len;
+ return len;
+}
+
+static const struct file_operations alloc_tag_ctx_file_ops = {
+ .owner = THIS_MODULE,
+ .open = alloc_tag_file_open,
+ .release = alloc_tag_file_release,
+ .read = alloc_tag_ctx_file_read,
+ .write = alloc_tag_ctx_file_write,
+};
+
static int dbgfs_init(struct codetag_type *cttype)
{
struct dentry *file;
+ struct dentry *ctx_file;

file = debugfs_create_file("alloc_tags", 0444, NULL, cttype,
&alloc_tag_file_ops);
+ if (IS_ERR(file))
+ return PTR_ERR(file);
+
+ ctx_file = debugfs_create_file("alloc_tags.ctx", 0666, NULL, cttype,
+ &alloc_tag_ctx_file_ops);
+ if (IS_ERR(ctx_file)) {
+ debugfs_remove(file);
+ return PTR_ERR(ctx_file);
+ }

- return IS_ERR(file) ? PTR_ERR(file) : 0;
+ return 0;
}

#else /* CONFIG_DEBUG_FS */
@@ -129,9 +360,10 @@ static int dbgfs_init(struct codetag_type *) { return 0; }

static void alloc_tag_module_unload(struct codetag_type *cttype, struct codetag_module *cmod)
{
- struct codetag_iterator iter = codetag_get_ct_iter(cttype);
+ struct codetag_iterator iter;
struct codetag *ct;

+ codetag_init_iter(&iter, cttype);
for (ct = codetag_next_ct(&iter); ct; ct = codetag_next_ct(&iter)) {
struct alloc_tag *tag = ct_to_alloc_tag(ct);

@@ -147,6 +379,7 @@ static int __init alloc_tag_init(void)
.section = "alloc_tags",
.tag_size = sizeof(struct alloc_tag),
.module_unload = alloc_tag_module_unload,
+ .free_ctx = alloc_tag_ops_free_ctx,
};

cttype = codetag_register_type(&desc);
diff --git a/lib/codetag.c b/lib/codetag.c
index 2762fda5c016..a936d2988c96 100644
--- a/lib/codetag.c
+++ b/lib/codetag.c
@@ -26,16 +26,14 @@ void codetag_lock_module_list(struct codetag_type *cttype, bool lock)
up_read(&cttype->mod_lock);
}

-struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype)
+void codetag_init_iter(struct codetag_iterator *iter,
+ struct codetag_type *cttype)
{
- struct codetag_iterator iter = {
- .cttype = cttype,
- .cmod = NULL,
- .mod_id = 0,
- .ct = NULL,
- };
-
- return iter;
+ iter->cttype = cttype;
+ iter->cmod = NULL;
+ iter->mod_id = 0;
+ iter->ct = NULL;
+ iter->ctx = NULL;
}

static inline struct codetag *get_first_module_ct(struct codetag_module *cmod)
@@ -127,6 +125,10 @@ struct codetag_ctx *codetag_next_ctx(struct codetag_iterator *iter)

lockdep_assert_held(&iter->cttype->mod_lock);

+ /* Move to the first codetag if search just started */
+ if (!iter->ct)
+ codetag_next_ct(iter);
+
if (!ctx)
return next_ctx_from_ct(iter);

--
2.37.2.672.g94769d06f0-goog