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blk-mq: use NOIO context to prevent deadlock during debugfs creation

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Creating debugfs entries can trigger fs reclaim, which can enter back
into the block layer request_queue. This can cause deadlock if the
queue is frozen.

Previously, a WARN_ON_ONCE check was used in debugfs_create_files()
to detect this condition, but it was racy since the queue can be frozen
from another context at any time.

Introduce blk_debugfs_lock()/blk_debugfs_unlock() helpers that combine
the debugfs_mutex with memalloc_noio_save()/restore() to prevent fs
reclaim from triggering block I/O. Also add blk_debugfs_lock_nomemsave()
and blk_debugfs_unlock_nomemrestore() variants for callers that don't
need NOIO protection (e.g., debugfs removal or read-only operations).

Replace all raw debugfs_mutex lock/unlock pairs with these helpers,
using the _nomemsave/_nomemrestore variants where appropriate.

Reported-by: Yi Zhang <yi.zhang@redhat.com>
Closes: https://lore.kernel.org/all/CAHj4cs9gNKEYAPagD9JADfO5UH+OiCr4P7OO2wjpfOYeM-RV=A@mail.gmail.com/
Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Closes: https://lore.kernel.org/all/aYWQR7CtYdk3K39g@shinmob/
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Yu Kuai <yukuai@fnnas.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Yu Kuai 2026-02-14 13:43:50 +08:00 • committed by Jens Axboe
parent 3678a334a5
commit dfe48ea179
6 changed files with 71 additions and 36 deletions
Download patch file Download diff file Expand all files Collapse all files

10
block/blk-mq-debugfs.c
View file

@ -613,11 +613,6 @@ static void debugfs_create_files(struct request_queue *q, struct dentry *parent,
const struct blk_mq_debugfs_attr *attr)
{
lockdep_assert_held(&q->debugfs_mutex);
/*
* Creating new debugfs entries with queue freezed has the risk of
* deadlock.
*/
WARN_ON_ONCE(q->mq_freeze_depth != 0);
/*
* debugfs_mutex should not be nested under other locks that can be
* grabbed while queue is frozen.
@ -693,12 +688,13 @@ void blk_mq_debugfs_unregister_hctx(struct blk_mq_hw_ctx *hctx)
void blk_mq_debugfs_register_hctxs(struct request_queue *q)
{
struct blk_mq_hw_ctx *hctx;
unsigned int memflags;
unsigned long i;
mutex_lock(&q->debugfs_mutex);
memflags = blk_debugfs_lock(q);
queue_for_each_hw_ctx(q, hctx, i)
blk_mq_debugfs_register_hctx(q, hctx);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
}
void blk_mq_debugfs_unregister_hctxs(struct request_queue *q)

9
block/blk-mq-sched.c
View file

@ -390,13 +390,14 @@ static void blk_mq_sched_tags_teardown(struct request_queue *q, unsigned int fla
void blk_mq_sched_reg_debugfs(struct request_queue *q)
{
struct blk_mq_hw_ctx *hctx;
unsigned int memflags;
unsigned long i;
mutex_lock(&q->debugfs_mutex);
memflags = blk_debugfs_lock(q);
blk_mq_debugfs_register_sched(q);
queue_for_each_hw_ctx(q, hctx, i)
blk_mq_debugfs_register_sched_hctx(q, hctx);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
}
void blk_mq_sched_unreg_debugfs(struct request_queue *q)
@ -404,11 +405,11 @@ void blk_mq_sched_unreg_debugfs(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
unsigned long i;
mutex_lock(&q->debugfs_mutex);
blk_debugfs_lock_nomemsave(q);
queue_for_each_hw_ctx(q, hctx, i)
blk_mq_debugfs_unregister_sched_hctx(hctx);
blk_mq_debugfs_unregister_sched(q);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock_nomemrestore(q);
}
void blk_mq_free_sched_tags(struct elevator_tags *et,

9
block/blk-sysfs.c
View file

@ -892,13 +892,13 @@ static void blk_debugfs_remove(struct gendisk *disk)
{
struct request_queue *q = disk->queue;
mutex_lock(&q->debugfs_mutex);
blk_debugfs_lock_nomemsave(q);
blk_trace_shutdown(q);
debugfs_remove_recursive(q->debugfs_dir);
q->debugfs_dir = NULL;
q->sched_debugfs_dir = NULL;
q->rqos_debugfs_dir = NULL;
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock_nomemrestore(q);
}
/**
@ -908,6 +908,7 @@ static void blk_debugfs_remove(struct gendisk *disk)
int blk_register_queue(struct gendisk *disk)
{
struct request_queue *q = disk->queue;
unsigned int memflags;
int ret;
ret = kobject_add(&disk->queue_kobj, &disk_to_dev(disk)->kobj, "queue");
@ -921,11 +922,11 @@ int blk_register_queue(struct gendisk *disk)
}
mutex_lock(&q->sysfs_lock);
mutex_lock(&q->debugfs_mutex);
memflags = blk_debugfs_lock(q);
q->debugfs_dir = debugfs_create_dir(disk->disk_name, blk_debugfs_root);
if (queue_is_mq(q))
blk_mq_debugfs_register(q);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
ret = disk_register_independent_access_ranges(disk);
if (ret)

10
block/blk-wbt.c
View file

@ -776,6 +776,7 @@ void wbt_init_enable_default(struct gendisk *disk)
{
struct request_queue *q = disk->queue;
struct rq_wb *rwb;
unsigned int memflags;
if (!__wbt_enable_default(disk))
return;
@ -789,9 +790,9 @@ void wbt_init_enable_default(struct gendisk *disk)
return;
}
mutex_lock(&q->debugfs_mutex);
memflags = blk_debugfs_lock(q);
blk_mq_debugfs_register_rq_qos(q);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
}
static u64 wbt_default_latency_nsec(struct request_queue *q)
@ -1015,9 +1016,10 @@ int wbt_set_lat(struct gendisk *disk, s64 val)
blk_mq_unquiesce_queue(q);
out:
blk_mq_unfreeze_queue(q, memflags);
mutex_lock(&q->debugfs_mutex);
memflags = blk_debugfs_lock(q);
blk_mq_debugfs_register_rq_qos(q);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
return ret;
}

31
block/blk.h
View file

@ -729,4 +729,35 @@ static inline void blk_unfreeze_release_lock(struct request_queue *q)
}
#endif
/*
* debugfs directory and file creation can trigger fs reclaim, which can enter
* back into the block layer request_queue. This can cause deadlock if the
* queue is frozen. Use NOIO context together with debugfs_mutex to prevent fs
* reclaim from triggering block I/O.
*/
static inline void blk_debugfs_lock_nomemsave(struct request_queue *q)
{
mutex_lock(&q->debugfs_mutex);
}
static inline void blk_debugfs_unlock_nomemrestore(struct request_queue *q)
{
mutex_unlock(&q->debugfs_mutex);
}
static inline unsigned int __must_check blk_debugfs_lock(struct request_queue *q)
{
unsigned int memflags = memalloc_noio_save();
blk_debugfs_lock_nomemsave(q);
return memflags;
}
static inline void blk_debugfs_unlock(struct request_queue *q,
unsigned int memflags)
{
blk_debugfs_unlock_nomemrestore(q);
memalloc_noio_restore(memflags);
}
#endif /* BLK_INTERNAL_H */

38
kernel/trace/blktrace.c
View file

@ -559,9 +559,9 @@ int blk_trace_remove(struct request_queue *q)
{
int ret;
mutex_lock(&q->debugfs_mutex);
blk_debugfs_lock_nomemsave(q);
ret = __blk_trace_remove(q);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock_nomemrestore(q);
return ret;
}
@ -767,6 +767,7 @@ int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
struct blk_user_trace_setup2 buts2;
struct blk_user_trace_setup buts;
struct blk_trace *bt;
unsigned int memflags;
int ret;
ret = copy_from_user(&buts, arg, sizeof(buts));
@ -785,16 +786,16 @@ int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
.pid = buts.pid,
};
mutex_lock(&q->debugfs_mutex);
memflags = blk_debugfs_lock(q);
bt = blk_trace_setup_prepare(q, name, dev, buts.buf_size, buts.buf_nr,
bdev);
if (IS_ERR(bt)) {
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
return PTR_ERR(bt);
}
blk_trace_setup_finalize(q, name, 1, bt, &buts2);
strscpy(buts.name, buts2.name, BLKTRACE_BDEV_SIZE);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
if (copy_to_user(arg, &buts, sizeof(buts))) {
blk_trace_remove(q);
@ -809,6 +810,7 @@ static int blk_trace_setup2(struct request_queue *q, char *name, dev_t dev,
{
struct blk_user_trace_setup2 buts2;
struct blk_trace *bt;
unsigned int memflags;
if (copy_from_user(&buts2, arg, sizeof(buts2)))
return -EFAULT;
@ -819,15 +821,15 @@ static int blk_trace_setup2(struct request_queue *q, char *name, dev_t dev,
if (buts2.flags != 0)
return -EINVAL;
mutex_lock(&q->debugfs_mutex);
memflags = blk_debugfs_lock(q);
bt = blk_trace_setup_prepare(q, name, dev, buts2.buf_size, buts2.buf_nr,
bdev);
if (IS_ERR(bt)) {
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
return PTR_ERR(bt);
}
blk_trace_setup_finalize(q, name, 2, bt, &buts2);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
if (copy_to_user(arg, &buts2, sizeof(buts2))) {
blk_trace_remove(q);
@ -844,6 +846,7 @@ static int compat_blk_trace_setup(struct request_queue *q, char *name,
struct blk_user_trace_setup2 buts2;
struct compat_blk_user_trace_setup cbuts;
struct blk_trace *bt;
unsigned int memflags;
if (copy_from_user(&cbuts, arg, sizeof(cbuts)))
return -EFAULT;
@ -860,15 +863,15 @@ static int compat_blk_trace_setup(struct request_queue *q, char *name,
.pid = cbuts.pid,
};
mutex_lock(&q->debugfs_mutex);
memflags = blk_debugfs_lock(q);
bt = blk_trace_setup_prepare(q, name, dev, buts2.buf_size, buts2.buf_nr,
bdev);
if (IS_ERR(bt)) {
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
return PTR_ERR(bt);
}
blk_trace_setup_finalize(q, name, 1, bt, &buts2);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
if (copy_to_user(arg, &buts2.name, ARRAY_SIZE(buts2.name))) {
blk_trace_remove(q);
@ -898,9 +901,9 @@ int blk_trace_startstop(struct request_queue *q, int start)
{
int ret;
mutex_lock(&q->debugfs_mutex);
blk_debugfs_lock_nomemsave(q);
ret = __blk_trace_startstop(q, start);
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock_nomemrestore(q);
return ret;
}
@ -2020,7 +2023,7 @@ static ssize_t sysfs_blk_trace_attr_show(struct device *dev,
struct blk_trace *bt;
ssize_t ret = -ENXIO;
mutex_lock(&q->debugfs_mutex);
blk_debugfs_lock_nomemsave(q);
bt = rcu_dereference_protected(q->blk_trace,
lockdep_is_held(&q->debugfs_mutex));
@ -2041,7 +2044,7 @@ static ssize_t sysfs_blk_trace_attr_show(struct device *dev,
ret = sprintf(buf, "%llu\n", bt->end_lba);
out_unlock_bdev:
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock_nomemrestore(q);
return ret;
}
@ -2052,6 +2055,7 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
struct block_device *bdev = dev_to_bdev(dev);
struct request_queue *q = bdev_get_queue(bdev);
struct blk_trace *bt;
unsigned int memflags;
u64 value;
ssize_t ret = -EINVAL;
@ -2071,7 +2075,7 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
goto out;
}
mutex_lock(&q->debugfs_mutex);
memflags = blk_debugfs_lock(q);
bt = rcu_dereference_protected(q->blk_trace,
lockdep_is_held(&q->debugfs_mutex));
@ -2106,7 +2110,7 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
}
out_unlock_bdev:
mutex_unlock(&q->debugfs_mutex);
blk_debugfs_unlock(q, memflags);
out:
return ret ? ret : count;
}