| Message ID | 20190912040224.7554-1-ming.lei@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: fix race between switching elevator and removing queues | expand |
On 9/11/19 10:02 PM, Ming Lei wrote: > 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. Thanks Ming, looks good to me and cleaner than before too.
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);
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> --- block/blk-sysfs.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)