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block: fix race between switching elevator and removing queues

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cecf5d87ff ("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: cecf5d87ff ("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: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2019-09-12 12:02:24 +08:00 committed by Jens Axboe
parent b804049dce
commit 0a67b5a926
1 changed files with 5 additions and 3 deletions
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8
block/blk-sysfs.c
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@ -1030,7 +1030,6 @@ EXPORT_SYMBOL_GPL(blk_register_queue);
void blk_unregister_queue(struct gendisk *disk)
{
struct request_queue *q = disk->queue;
bool has_elevator;
if (WARN_ON(!q))
return;
@ -1046,7 +1045,6 @@ void blk_unregister_queue(struct gendisk *disk)
*/
mutex_lock(&q->sysfs_lock);
blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
has_elevator = !!q->elevator;
mutex_unlock(&q->sysfs_lock);
mutex_lock(&q->sysfs_dir_lock);
@ -1061,7 +1059,11 @@ void blk_unregister_queue(struct gendisk *disk)
kobject_del(&q->kobj);
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);
mutex_unlock(&q->sysfs_dir_lock);