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block: fix warning when I/O elevator is changed as request_queue is being removed
There is a race between changing I/O elevator and request_queue removal which can trigger the warning in kobject_add_internal. A program can use sysfs to request a change of elevator at the same time another task is unregistering the request_queue the elevator would be attached to. The elevator's kobject will then attempt to be connected to the request_queue in the object tree when the request_queue has just been removed from sysfs. This triggers the warning in kobject_add_internal as the request_queue no longer has a sysfs directory: kobject_add_internal failed for iosched (error: -2 parent: queue) ------------[ cut here ]------------ WARNING: CPU: 3 PID: 14075 at lib/kobject.c:244 kobject_add_internal+0x103/0x2d0 To fix this warning, we can check the QUEUE_FLAG_REGISTERED flag when changing the elevator and use the request_queue's sysfs_lock to serialize between clearing the flag and the elevator testing the flag. Signed-off-by: David Jeffery <djeffery@redhat.com> Tested-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@ -931,7 +931,9 @@ void blk_unregister_queue(struct gendisk *disk)
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if (WARN_ON(!q))
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return;
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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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wbt_exit(q);
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@ -1055,6 +1055,10 @@ static int __elevator_change(struct request_queue *q, const char *name)
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char elevator_name[ELV_NAME_MAX];
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struct elevator_type *e;
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/* Make sure queue is not in the middle of being removed */
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if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags))
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return -ENOENT;
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/*
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* Special case for mq, turn off scheduling
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*/
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