Commit 0a67b5a9 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe

block: fix race between switching elevator and removing queues

cecf5d87 ("block: split .sysfs_lock into two locks") starts to
release & actuire sysfs_lock again during switching elevator. So it
isn't enough to prevent switching elevator from happening by simply
clearing QUEUE_FLAG_REGISTERED with holding sysfs_lock, because
in-progress switch still can move on after re-acquiring the lock,
meantime the flag of QUEUE_FLAG_REGISTERED won't get checked.

Fixes this issue by checking 'q->elevator' directly & locklessly after
q->kobj is removed in blk_unregister_queue(), this way is safe because
q->elevator can't be changed at that time.

Fixes: cecf5d87 ("block: split .sysfs_lock into two locks")
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent b804049d
...@@ -1030,7 +1030,6 @@ EXPORT_SYMBOL_GPL(blk_register_queue); ...@@ -1030,7 +1030,6 @@ EXPORT_SYMBOL_GPL(blk_register_queue);
void blk_unregister_queue(struct gendisk *disk) void blk_unregister_queue(struct gendisk *disk)
{ {
struct request_queue *q = disk->queue; struct request_queue *q = disk->queue;
bool has_elevator;
if (WARN_ON(!q)) if (WARN_ON(!q))
return; return;
...@@ -1046,7 +1045,6 @@ void blk_unregister_queue(struct gendisk *disk) ...@@ -1046,7 +1045,6 @@ void blk_unregister_queue(struct gendisk *disk)
*/ */
mutex_lock(&q->sysfs_lock); mutex_lock(&q->sysfs_lock);
blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q); blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
has_elevator = !!q->elevator;
mutex_unlock(&q->sysfs_lock); mutex_unlock(&q->sysfs_lock);
mutex_lock(&q->sysfs_dir_lock); mutex_lock(&q->sysfs_dir_lock);
...@@ -1061,7 +1059,11 @@ void blk_unregister_queue(struct gendisk *disk) ...@@ -1061,7 +1059,11 @@ void blk_unregister_queue(struct gendisk *disk)
kobject_del(&q->kobj); kobject_del(&q->kobj);
blk_trace_remove_sysfs(disk_to_dev(disk)); blk_trace_remove_sysfs(disk_to_dev(disk));
if (has_elevator) /*
* q->kobj has been removed, so it is safe to check if elevator
* exists without holding q->sysfs_lock.
*/
if (q->elevator)
elv_unregister_queue(q); elv_unregister_queue(q);
mutex_unlock(&q->sysfs_dir_lock); mutex_unlock(&q->sysfs_dir_lock);
......
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