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block: properly protect the 'queue' kobj in blk_unregister_queue
The original commite9a823fb34
(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:e9a823fb34
("block: fix warning when I/O elevator is changed as request_queue is being removed") Signed-off-by: Mike Snitzer <snitzer@redhat.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@ -248,7 +248,7 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx)
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return ret;
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}
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static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
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void blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
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{
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struct blk_mq_hw_ctx *hctx;
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int i;
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@ -265,13 +265,6 @@ static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
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q->mq_sysfs_init_done = false;
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}
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void blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
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{
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mutex_lock(&q->sysfs_lock);
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__blk_mq_unregister_dev(dev, q);
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mutex_unlock(&q->sysfs_lock);
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}
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void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx)
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{
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kobject_init(&hctx->kobj, &blk_mq_hw_ktype);
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@ -929,13 +929,18 @@ void blk_unregister_queue(struct gendisk *disk)
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if (WARN_ON(!q))
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return;
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/*
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* Protect against the 'queue' kobj being accessed
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* while/after it is removed.
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*/
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mutex_lock(&q->sysfs_lock);
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queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q);
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mutex_unlock(&q->sysfs_lock);
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spin_lock_irq(q->queue_lock);
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queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
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spin_unlock_irq(q->queue_lock);
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wbt_exit(q);
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if (q->mq_ops)
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blk_mq_unregister_dev(disk_to_dev(disk), q);
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@ -946,4 +951,6 @@ void blk_unregister_queue(struct gendisk *disk)
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kobject_del(&q->kobj);
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blk_trace_remove_sysfs(disk_to_dev(disk));
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kobject_put(&disk_to_dev(disk)->kobj);
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mutex_unlock(&q->sysfs_lock);
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}
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