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 <h...@infradead.org>
Cc: Hannes Reinecke <h...@suse.com>
Cc: Greg KH <gre...@linuxfoundation.org>
Cc: Mike Snitzer <snit...@redhat.com>
Cc: Bart Van Assche <bvanass...@acm.org>
Signed-off-by: Ming Lei <ming....@redhat.com>
---
block/blk-sysfs.c | 8 +++++---
1 file 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);
--
2.20.1
