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Date: Mon, 22 Apr 2013 14:23:24 -0700
From: Kent Overstreet <koverstreet@google.com>
To: Namjae Jeon <linkinjeon@gmail.com>
Subject: Re: [PATCH v2 0/9] fix max discard sectors limit
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Cc: axboe@kernel.dk, nbd-general@lists.sourceforge.net,
 linux-raid@vger.kernel.org, npiggin@kernel.dk, linux-scsi@vger.kernel.org,
 neilb@suse.de, dwmw2@infradead.org, Namjae Jeon <namjae.jeon@samsung.com>,
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On Sat, Apr 20, 2013 at 01:40:02AM +0900, Namjae Jeon wrote:
> From: Namjae Jeon <namjae.jeon@samsung.com>
> 
> linux-v3.8-rc1 and later support for plug for blkdev_issue_discard with
> commit 0cfbcafcae8b7364b5fa96c2b26ccde7a3a296a9 
> (block: add plug for blkdev_issue_discard )
> 
> For example,
> 1) DISCARD rq-1 with size size 4GB
> 2) DISCARD rq-2 with size size 1GB
> 
> If these 2 discard requests get merged, final request size will be 5GB.
> 
> In this case, request's __data_len field may overflow as it can store
> max 4GB(unsigned int).

Complete NACK - like James said, this fix is nonsensical. This should be
fixed by just checking for overflow before merging requests, not with
weird hacks in the drivers.