linux-kernel - Re: [PATCH 1/5] Block: Discard may need to allocate pages

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Date:	Fri, 17 Apr 2009 17:23:42 -0400
From:	Mark Lord <liml@....ca>
To:	Matthew Wilcox <willy@...ux.intel.com>
Cc:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	jgarzik@...hat.com, Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCH 1/5] Block: Discard may need to allocate pages

Matthew Wilcox wrote:
> From: Matthew Wilcox <matthew@....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@...ux.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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