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Date: Thu, 17 Jan 2013 11:04:38 +0000
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
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        Subhash Jadavani <subhashj@codeaurora.org>, Tejun Heo <tj@kernel.org>,
        asias@redhat.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 1/1] block: blk-merge: don't merge the pages with
	non-contiguous descriptors
Message-ID: <20130117110438.GZ23505@n2100.arm.linux.org.uk>
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On Thu, Jan 17, 2013 at 11:01:47AM +0000, James Bottomley wrote:
> On Thu, 2013-01-17 at 10:47 +0000, Russell King - ARM Linux wrote:
> > Also, couldn't the addition of the scatterlist offset to the page also
> > be buggy too?
> 
> No, fortunately, offset must be within the first page from the point of
> view of block generated sg lists.  As long as nothing within arm
> violates this, it should be a safe assumption ... although the code
> seems to assume otherwise.

Are you absolutely sure about that?  I believe I have seen cases where
that has been violated in the past, though it was many years ago.