Re: [PATCH] block: Check that queue is alive in blk_insert_cloned_request()

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

On Jul 08 Roland Dreier wrote:
> This fixes crashes such as the below that I see when the storage
> underlying a dm-multipath device is hot-removed.  The problem is that
> dm requeues a request to a device whose block queue has already been
> cleaned up, and blk_insert_cloned_request() doesn't check if the queue
> is alive, but rather goes ahead and tries to queue the request.  This
> ends up dereferencing the elevator that was already freed in
> blk_cleanup_queue().
[...]
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1706,6 +1706,9 @@ int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
>  		return -EIO;
>  #endif
>  
> +	if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
> +		return -EIO;
> +
>  	spin_lock_irqsave(q->queue_lock, flags);
>  
>  	/*

Not knowing the calling contexts or having tried to learn about them, I am
wondering:  What prevents the elevator to be freed right after the flag
was checked?
-- 
Stefan Richter
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http://arcgraph.de/sr/