From: Ming Lei <ming.lei@redhat.com> mainline inclusion from mainline-5.4-rc1 commit 0a67b5a926e63ff5492c3c675eab5900580d056d category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I6HOKY CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h... --------------------------- 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> Conflict: block/blk-sysfs.c Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com> Reviewed-by: Hou Tao <houtao1@huawei.com> Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.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 d925b75702e3..a663dbcbdd19 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -1020,7 +1020,6 @@ 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; @@ -1038,7 +1037,6 @@ 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); @@ -1051,7 +1049,11 @@ void blk_unregister_queue(struct gendisk *disk) blk_trace_remove_sysfs(disk_to_dev(disk)); - if (q->request_fn || (q->mq_ops && has_elevator)) + /* + * q->kobj has been removed, so it is safe to check if elevator + * exists without holding q->sysfs_lock. + */ + if (q->request_fn || (q->mq_ops && q->elevator)) elv_unregister_queue(q); mutex_unlock(&q->sysfs_dir_lock); -- 2.25.1