linux-kernel - Re: [PATCH] block: Check that queue is alive in blk_insert_cloned

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Message-ID: <20110709110538.35e1ea1e@stein>
Date:	Sat, 9 Jul 2011 11:05:38 +0200
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Roland Dreier <roland@...nel.org>
Cc:	Jens Axboe <axboe@...nel.dk>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-scsi@...r.kernel.org,
	Steffen Maier <maier@...ux.vnet.ibm.com>,
	"Manvanthara B. Puttashankar" <manvanth@...ux.vnet.ibm.com>,
	Tarak Reddy <tarak.reddy@...ibm.com>,
	"Seshagiri N. Ippili" <sesh17@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: Check that queue is alive in
 blk_insert_cloned_request()

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
-=====-==-== -=== -=--=
http://arcgraph.de/sr/
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