Message-ID: <49E8F35E.2060103@rtr.ca>
Date: Fri, 17 Apr 2009 17:23:42 -0400
From: Mark Lord <liml@rtr.ca>
Organization: Real-Time Remedies Inc.
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To: Matthew Wilcox <willy@linux.intel.com>
Cc: linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org,
       jgarzik@redhat.com, Matthew Wilcox <matthew@wil.cx>
Subject: Re: [PATCH 1/5] Block: Discard may need to allocate pages
References: <1238683047-13588-1-git-send-email-willy@linux.intel.com>
In-Reply-To: <1238683047-13588-1-git-send-email-willy@linux.intel.com>
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Matthew Wilcox wrote:
> From: Matthew Wilcox <matthew@wil.cx>
> 
> SCSI and ATA both need to send data to the device.  In order to do this,
> the BIO must be allocated with room for a page to be added, and the bio
> needs to be passed to the discard prep function.  We also need to free
> the page attached to the BIO before we free it.
> 
> init_request_from_bio() is not currently called from a context which
> forbids sleeping, and to make sure it stays that way (so we don't have
> to use GFP_ATOMIC), add a might_sleep() to it.
> 
> Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
...
> @@ -1118,7 +1120,7 @@ void init_request_from_bio(struct request *req, struct bio *bio)
>  		req->cmd_flags |= REQ_DISCARD;
>  		if (bio_barrier(bio))
>  			req->cmd_flags |= REQ_SOFTBARRIER;
> -		req->q->prepare_discard_fn(req->q, req);
> +		req->q->prepare_discard_fn(req->q, req, bio);
>  	} else if (unlikely(bio_barrier(bio)))
>  		req->cmd_flags |= (REQ_HARDBARRIER | REQ_NOMERGE);
>  
..

Matthew, note that prepare_discardfn() may fail,
and return an error result.  The above code does not
check for this or handle it very well.

Cheers
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