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mm: mmap_lock: replace get_memcg_path_buf() with on-stack buffer

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Commit 2b5067a814 ("mm: mmap_lock: add tracepoints around lock
acquisition") introduced TRACE_MMAP_LOCK_EVENT() macro using
preempt_disable() in order to let get_mm_memcg_path() return a percpu
buffer exclusively used by normal, softirq, irq and NMI contexts
respectively.

Commit 832b507253 ("mm: mmap_lock: use local locks instead of disabling
preemption") replaced preempt_disable() with local_lock(&memcg_paths.lock)
based on an argument that preempt_disable() has to be avoided because
get_mm_memcg_path() might sleep if PREEMPT_RT=y.

But syzbot started reporting

  inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.

and

  inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.

messages, for local_lock() does not disable IRQ.

We could replace local_lock() with local_lock_irqsave() in order to
suppress these messages.  But this patch instead replaces percpu buffers
with on-stack buffer, for the size of each buffer returned by
get_memcg_path_buf() is only 256 bytes which is tolerable for allocating
from current thread's kernel stack memory.

Link: https://lkml.kernel.org/r/ef22d289-eadb-4ed9-863b-fbc922b33d8d@I-love.SAKURA.ne.jp
Reported-by: syzbot <syzbot+40905bca570ae6784745@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=40905bca570ae6784745
Fixes: 832b507253 ("mm: mmap_lock: use local locks instead of disabling preemption")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Tetsuo Handa 2024-06-21 10:08:41 +09:00 committed by Andrew Morton
parent b1a80f4be7
commit 7d6be67cfd
1 changed files with 20 additions and 155 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

171
mm/mmap_lock.c
View File

@ -19,14 +19,7 @@ EXPORT_TRACEPOINT_SYMBOL(mmap_lock_released);
#ifdef CONFIG_MEMCG
/*
* Our various events all share the same buffer (because we don't want or need
* to allocate a set of buffers *per event type*), so we need to protect against
* concurrent _reg() and _unreg() calls, and count how many _reg() calls have
* been made.
*/
static DEFINE_MUTEX(reg_lock);
static int reg_refcount; /* Protected by reg_lock. */
static atomic_t reg_refcount;
/*
* Size of the buffer for memcg path names. Ignoring stack trace support,
@ -34,136 +27,22 @@ static int reg_refcount; /* Protected by reg_lock. */
*/
#define MEMCG_PATH_BUF_SIZE MAX_FILTER_STR_VAL
/*
* How many contexts our trace events might be called in: normal, softirq, irq,
* and NMI.
*/
#define CONTEXT_COUNT 4
struct memcg_path {
local_lock_t lock;
char __rcu *buf;
local_t buf_idx;
};
static DEFINE_PER_CPU(struct memcg_path, memcg_paths) = {
.lock = INIT_LOCAL_LOCK(lock),
.buf_idx = LOCAL_INIT(0),
};
static char **tmp_bufs;
/* Called with reg_lock held. */
static void free_memcg_path_bufs(void)
{
struct memcg_path *memcg_path;
int cpu;
char **old = tmp_bufs;
for_each_possible_cpu(cpu) {
memcg_path = per_cpu_ptr(&memcg_paths, cpu);
*(old++) = rcu_dereference_protected(memcg_path->buf,
lockdep_is_held(&reg_lock));
rcu_assign_pointer(memcg_path->buf, NULL);
}
/* Wait for inflight memcg_path_buf users to finish. */
synchronize_rcu();
old = tmp_bufs;
for_each_possible_cpu(cpu) {
kfree(*(old++));
}
kfree(tmp_bufs);
tmp_bufs = NULL;
}
int trace_mmap_lock_reg(void)
{
int cpu;
char *new;
mutex_lock(&reg_lock);
/* If the refcount is going 0->1, proceed with allocating buffers. */
if (reg_refcount++)
goto out;
tmp_bufs = kmalloc_array(num_possible_cpus(), sizeof(*tmp_bufs),
GFP_KERNEL);
if (tmp_bufs == NULL)
goto out_fail;
for_each_possible_cpu(cpu) {
new = kmalloc(MEMCG_PATH_BUF_SIZE * CONTEXT_COUNT, GFP_KERNEL);
if (new == NULL)
goto out_fail_free;
rcu_assign_pointer(per_cpu_ptr(&memcg_paths, cpu)->buf, new);
/* Don't need to wait for inflights, they'd have gotten NULL. */
}
out:
mutex_unlock(&reg_lock);
atomic_inc(&reg_refcount);
return 0;
out_fail_free:
free_memcg_path_bufs();
out_fail:
/* Since we failed, undo the earlier ref increment. */
--reg_refcount;
mutex_unlock(&reg_lock);
return -ENOMEM;
}
void trace_mmap_lock_unreg(void)
{
mutex_lock(&reg_lock);
/* If the refcount is going 1->0, proceed with freeing buffers. */
if (--reg_refcount)
goto out;
free_memcg_path_bufs();
out:
mutex_unlock(&reg_lock);
}
static inline char *get_memcg_path_buf(void)
{
struct memcg_path *memcg_path = this_cpu_ptr(&memcg_paths);
char *buf;
int idx;
rcu_read_lock();
buf = rcu_dereference(memcg_path->buf);
if (buf == NULL) {
rcu_read_unlock();
return NULL;
}
idx = local_add_return(MEMCG_PATH_BUF_SIZE, &memcg_path->buf_idx) -
MEMCG_PATH_BUF_SIZE;
return &buf[idx];
}
static inline void put_memcg_path_buf(void)
{
local_sub(MEMCG_PATH_BUF_SIZE, &this_cpu_ptr(&memcg_paths)->buf_idx);
rcu_read_unlock();
atomic_dec(&reg_refcount);
}
#define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \
do { \
const char *memcg_path; \
local_lock(&memcg_paths.lock); \
memcg_path = get_mm_memcg_path(mm); \
trace_mmap_lock_##type(mm, \
memcg_path != NULL ? memcg_path : "", \
##__VA_ARGS__); \
if (likely(memcg_path != NULL)) \
put_memcg_path_buf(); \
local_unlock(&memcg_paths.lock); \
char buf[MEMCG_PATH_BUF_SIZE]; \
get_mm_memcg_path(mm, buf, sizeof(buf)); \
trace_mmap_lock_##type(mm, buf, ##__VA_ARGS__); \
} while (0)
#else /* !CONFIG_MEMCG */
@ -185,37 +64,23 @@ void trace_mmap_lock_unreg(void)
#ifdef CONFIG_TRACING
#ifdef CONFIG_MEMCG
/*
* Write the given mm_struct's memcg path to a percpu buffer, and return a
* pointer to it. If the path cannot be determined, or no buffer was available
* (because the trace event is being unregistered), NULL is returned.
*
* Note: buffers are allocated per-cpu to avoid locking, so preemption must be
* disabled by the caller before calling us, and re-enabled only after the
* caller is done with the pointer.
*
* The caller must call put_memcg_path_buf() once the buffer is no longer
* needed. This must be done while preemption is still disabled.
* Write the given mm_struct's memcg path to a buffer. If the path cannot be
* determined or the trace event is being unregistered, empty string is written.
*/
static const char *get_mm_memcg_path(struct mm_struct *mm)
static void get_mm_memcg_path(struct mm_struct *mm, char *buf, size_t buflen)
{
char *buf = NULL;
struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm);
struct mem_cgroup *memcg;
buf[0] = '\0';
/* No need to get path if no trace event is registered. */
if (!atomic_read(&reg_refcount))
return;
memcg = get_mem_cgroup_from_mm(mm);
if (memcg == NULL)
goto out;
if (unlikely(memcg->css.cgroup == NULL))
goto out_put;
buf = get_memcg_path_buf();
if (buf == NULL)
goto out_put;
cgroup_path(memcg->css.cgroup, buf, MEMCG_PATH_BUF_SIZE);
out_put:
return;
if (memcg->css.cgroup)
cgroup_path(memcg->css.cgroup, buf, buflen);
css_put(&memcg->css);
out:
return buf;
}
#endif /* CONFIG_MEMCG */