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_mutex_lock()/blk_debugfs_mutex_unlock() helpers that combine the debugfs_mutex with memalloc_noio_save()/restore() to prevent fs reclaim from triggering block I/O. Replace all raw debugfs_mutex lock/unlock pairs with these helpers. Reported-by: Yi Zhang <[email protected]> Closes: https://lore.kernel.org/all/CAHj4cs9gNKEYAPagD9JADfO5UH+OiCr4P7OO2wjpfOYeM-RV=a...@mail.gmail.com/ Reported-by: Shinichiro Kawasaki <[email protected]> Closes: https://lore.kernel.org/all/aYWQR7CtYdk3K39g@shinmob/ Suggested-by: Christoph Hellwig <[email protected]> Signed-off-by: Yu Kuai <[email protected]> --- block/blk-mq-debugfs.c | 10 +++------- block/blk-mq-sched.c | 10 ++++++---- block/blk-sysfs.c | 10 ++++++---- block/blk-wbt.c | 10 ++++++---- block/blk.h | 21 +++++++++++++++++++++ kernel/trace/blktrace.c | 41 ++++++++++++++++++++++++----------------- 6 files changed, 66 insertions(+), 36 deletions(-) diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c index faeaa1fc86a7..28167c9baa55 100644 --- a/block/blk-mq-debugfs.c +++ b/block/blk-mq-debugfs.c @@ -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) diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index e26898128a7e..2cd07fe65e40 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -390,25 +390,27 @@ 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) { 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_unregister_sched_hctx(hctx); blk_mq_debugfs_unregister_sched(q); - mutex_unlock(&q->debugfs_mutex); + blk_debugfs_unlock(q, memflags); } void blk_mq_free_sched_tags(struct elevator_tags *et, diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 003aa684e854..31967a2867f7 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -891,14 +891,15 @@ const struct kobj_type blk_queue_ktype = { static void blk_debugfs_remove(struct gendisk *disk) { struct request_queue *q = disk->queue; + unsigned int memflags; - mutex_lock(&q->debugfs_mutex); + memflags = blk_debugfs_lock(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(q, memflags); } /** @@ -908,6 +909,7 @@ 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 +923,11 @@ 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) diff --git a/block/blk-wbt.c b/block/blk-wbt.c index 1415f2bf8611..6dba71e87387 100644 --- a/block/blk-wbt.c +++ b/block/blk-wbt.c @@ -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; } diff --git a/block/blk.h b/block/blk.h index 401d19ed08a6..d4f193814110 100644 --- a/block/blk.h +++ b/block/blk.h @@ -740,4 +740,25 @@ 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 unsigned int blk_debugfs_lock(struct request_queue *q) +{ + unsigned int memflags = memalloc_noio_save(); + + mutex_lock(&q->debugfs_mutex); + return memflags; +} + +static inline void blk_debugfs_unlock(struct request_queue *q, + unsigned int memflags) +{ + mutex_unlock(&q->debugfs_mutex); + memalloc_noio_restore(memflags); +} + #endif /* BLK_INTERNAL_H */ diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c index c4db5c2e7103..bc938b80702d 100644 --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -557,11 +557,12 @@ static int __blk_trace_remove(struct request_queue *q) int blk_trace_remove(struct request_queue *q) { + unsigned int memflags; int ret; - mutex_lock(&q->debugfs_mutex); + memflags = blk_debugfs_lock(q); ret = __blk_trace_remove(q); - mutex_unlock(&q->debugfs_mutex); + blk_debugfs_unlock(q, memflags); return ret; } @@ -767,6 +768,7 @@ 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 +787,16 @@ 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 +811,7 @@ 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 +822,15 @@ 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 +847,7 @@ 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 +864,15 @@ 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); @@ -896,11 +900,12 @@ static int __blk_trace_startstop(struct request_queue *q, int start) int blk_trace_startstop(struct request_queue *q, int start) { + unsigned int memflags; int ret; - mutex_lock(&q->debugfs_mutex); + memflags = blk_debugfs_lock(q); ret = __blk_trace_startstop(q, start); - mutex_unlock(&q->debugfs_mutex); + blk_debugfs_unlock(q, memflags); return ret; } @@ -2018,9 +2023,10 @@ static ssize_t sysfs_blk_trace_attr_show(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; ssize_t ret = -ENXIO; - mutex_lock(&q->debugfs_mutex); + memflags = blk_debugfs_lock(q); bt = rcu_dereference_protected(q->blk_trace, lockdep_is_held(&q->debugfs_mutex)); @@ -2041,7 +2047,7 @@ 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(q, memflags); return ret; } @@ -2052,6 +2058,7 @@ 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 +2078,7 @@ 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 +2113,7 @@ 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; } -- 2.51.0
