From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 12 Jan 2018 11:03:52 -0500 From: Mike Snitzer To: axboe@kernel.dk Cc: David Jeffery , Ming Lei , linux-block@vger.kernel.org, dm-devel@redhat.com, Bart.VanAssche@wdc.com Subject: [for-4.16 PATCH v6 2/4] block: properly protect the 'queue' kobj in blk_unregister_queue Message-ID: <20180112160352.GA6270@redhat.com> References: <20180112150606.6037-1-snitzer@redhat.com> <20180112150606.6037-3-snitzer@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20180112150606.6037-3-snitzer@redhat.com> List-ID: The original commit e9a823fb34a8b (block: fix warning when I/O elevator is changed as request_queue is being removed) is pretty conflated. "conflated" because the resource being protected by q->sysfs_lock isn't the queue_flags (it is the 'queue' kobj). q->sysfs_lock serializes __elevator_change() (via elv_iosched_store) from racing with blk_unregister_queue(): 1) By holding q->sysfs_lock first, __elevator_change() can complete before a racing blk_unregister_queue(). 2) Conversely, __elevator_change() is testing for QUEUE_FLAG_REGISTERED in case elv_iosched_store() loses the race with blk_unregister_queue(), it needs a way to know the 'queue' kobj isn't there. Expand the scope of blk_unregister_queue()'s q->sysfs_lock use so it is held until after the 'queue' kobj is removed. To do so blk_mq_unregister_dev() must not also take q->sysfs_lock. So rename __blk_mq_unregister_dev() to blk_mq_unregister_dev(). Also, blk_unregister_queue() should use q->queue_lock to protect against any concurrent writes to q->queue_flags -- even though chances are the queue is being cleaned up so no concurrent writes are likely. Fixes: e9a823fb34a8b ("block: fix warning when I/O elevator is changed as request_queue is being removed") Signed-off-by: Mike Snitzer --- block/blk-mq-sysfs.c | 9 +-------- block/blk-sysfs.c | 13 ++++++++++--- 2 files changed, 11 insertions(+), 11 deletions(-) v6: blk_mq_unregister_dev now requires q->sysfs_lock be held, Ming: I am not seeing any lockdep complaints with this. I've tested bio-based, blk-mq and old .request_fn request-based. diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c index 79969c3c234f..a54b4b070f1c 100644 --- a/block/blk-mq-sysfs.c +++ b/block/blk-mq-sysfs.c @@ -248,7 +248,7 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx) return ret; } -static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q) +void blk_mq_unregister_dev(struct device *dev, struct request_queue *q) { struct blk_mq_hw_ctx *hctx; int i; @@ -265,13 +265,6 @@ static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q) q->mq_sysfs_init_done = false; } -void blk_mq_unregister_dev(struct device *dev, struct request_queue *q) -{ - mutex_lock(&q->sysfs_lock); - __blk_mq_unregister_dev(dev, q); - mutex_unlock(&q->sysfs_lock); -} - void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx) { kobject_init(&hctx->kobj, &blk_mq_hw_ktype); diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 870484eaed1f..9272452ff456 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -929,12 +929,17 @@ void blk_unregister_queue(struct gendisk *disk) if (WARN_ON(!q)) return; + /* + * Protect against the 'queue' kobj being accessed + * while/after it is removed. + */ mutex_lock(&q->sysfs_lock); - queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q); - mutex_unlock(&q->sysfs_lock); - wbt_exit(q); + spin_lock_irq(q->queue_lock); + queue_flag_clear(QUEUE_FLAG_REGISTERED, q); + spin_unlock_irq(q->queue_lock); + wbt_exit(q); if (q->mq_ops) blk_mq_unregister_dev(disk_to_dev(disk), q); @@ -946,4 +951,6 @@ void blk_unregister_queue(struct gendisk *disk) kobject_del(&q->kobj); blk_trace_remove_sysfs(disk_to_dev(disk)); kobject_put(&disk_to_dev(disk)->kobj); + + mutex_unlock(&q->sysfs_lock); } -- 2.15.0