linux-kernel - Re: [PATCH v3 2/2] lib/scatterlist: use page iterator in the mapping iterator

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Date:	Sat, 23 Feb 2013 22:04:06 +0200
From:	Imre Deak <imre.deak@...el.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Tejun Heo <tj@...nel.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linaro-mm-sig@...ts.linaro.org,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] lib/scatterlist: use page iterator in the
 mapping iterator

On Fri, 2013-02-22 at 21:29 -0700, Stephen Warren wrote:
> On 02/13/2013 08:10 AM, Imre Deak wrote:
> > For better code reuse use the newly added page iterator to iterate
> > through the pages. The offset, length within the page is still
> > calculated by the mapping iterator as well as the actual mapping.
> > Idea from Tejun Heo <tj@...nel.org>.
> 
> This patch appears in linux-next since next-20130220. It breaks mounting
> a root filesystem on an SD card on the Raspberry Pi ARM platform, with
> errors such as those shown below.
> 
> next-20130222 with just this patch reverted works fine.

Thanks for tracking this down. I noticed now an obvious mistake I've
made, not limiting the mapping size to page size :/ I didn't hit it
since it only causes a problem when the user of miter modifies
miter->consumed and I think nothing does this on my machine. Since the
sdhci driver on Raspberry Pi does this the following might fix the
problem you saw. Could you give it a try? It applies on top of
v4 of the patch [1]:

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 2645acf..b83c144 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -493,6 +493,8 @@ bool sg_miter_next(struct sg_mapping_iter *miter)
 		miter->__offset = pgoffset ? 0 : sg->offset;
 		miter->__remaining = sg->offset + sg->length -
 				(pgoffset << PAGE_SHIFT) - miter->__offset;
+		miter->__remaining = min_t(unsigned long, miter->__remaining,
+					   PAGE_SIZE - miter->__offset);
 	}
 	miter->page = miter->piter.page;
 	miter->consumed = miter->length = miter->__remaining;


--Imre

[1]
http://lists.linaro.org/pipermail/linaro-mm-sig/2013-February/003069.html

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