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authorMing Lei <ming.lei@redhat.com>2019-09-12 12:02:24 +0800
committerJens Axboe <axboe@kernel.dk>2019-09-12 07:13:22 -0600
commit0a67b5a926e63ff5492c3c675eab5900580d056d (patch)
tree46b1761c8dc89e466d14e20abd659a3e76a1ca24 /block
parentb804049dce9128a88558bc1594ff96d6632fbc10 (diff)
block: fix race between switching elevator and removing queues
cecf5d87ff20 ("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: cecf5d87ff20 ("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>
Diffstat (limited to 'block')
-rw-r--r--block/blk-sysfs.c8
1 files changed, 5 insertions, 3 deletions
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 107513495220..3af79831e717 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -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);

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