linux-kernel - [PATCH 3.2 87/87] lib/scatterlist.c: don't flush_kernel_dcache

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Message-ID: <lsq.1385387069.245392394@decadent.org.uk>
Date:	Mon, 25 Nov 2013 13:44:29 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Will Deacon" <will.deacon@....com>,
	"FUJITA Tomonori" <fujita.tomonori@....ntt.co.jp>,
	"Jens Axboe" <axboe@...nel.dk>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Simon Baatz" <gmbnomis@...il.com>,
	"Ming Lei" <ming.lei@...onical.com>,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	"Aaro Koskinen" <aaro.koskinen@....fi>,
	"Catalin Marinas" <catalin.marinas@....com>,
	"Tejun Heo" <tj@...nel.org>,
	"Russell King - ARM Linux" <linux@....linux.org.uk>
Subject: [PATCH 3.2 87/87] lib/scatterlist.c: don't flush_kernel_dcache_page
 on slab page

3.2.53-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ming Lei <ming.lei@...onical.com>

commit 3d77b50c5874b7e923be946ba793644f82336b75 upstream.

Commit b1adaf65ba03 ("[SCSI] block: add sg buffer copy helper
functions") introduces two sg buffer copy helpers, and calls
flush_kernel_dcache_page() on pages in SG list after these pages are
written to.

Unfortunately, the commit may introduce a potential bug:

 - Before sending some SCSI commands, kmalloc() buffer may be passed to
   block layper, so flush_kernel_dcache_page() can see a slab page
   finally

 - According to cachetlb.txt, flush_kernel_dcache_page() is only called
   on "a user page", which surely can't be a slab page.

 - ARCH's implementation of flush_kernel_dcache_page() may use page
   mapping information to do optimization so page_mapping() will see the
   slab page, then VM_BUG_ON() is triggered.

Aaro Koskinen reported the bug on ARM/kirkwood when DEBUG_VM is enabled,
and this patch fixes the bug by adding test of '!PageSlab(miter->page)'
before calling flush_kernel_dcache_page().

Signed-off-by: Ming Lei <ming.lei@...onical.com>
Reported-by: Aaro Koskinen <aaro.koskinen@....fi>
Tested-by: Simon Baatz <gmbnomis@...il.com>
Cc: Russell King - ARM Linux <linux@....linux.org.uk>
Cc: Will Deacon <will.deacon@....com>
Cc: Aaro Koskinen <aaro.koskinen@....fi>
Acked-by: Catalin Marinas <catalin.marinas@....com>
Cc: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc: Tejun Heo <tj@...nel.org>
Cc: "James E.J. Bottomley" <JBottomley@...allels.com>
Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 lib/scatterlist.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -419,7 +419,8 @@ void sg_miter_stop(struct sg_mapping_ite
 	if (miter->addr) {
 		miter->__offset += miter->consumed;
 
-		if (miter->__flags & SG_MITER_TO_SG)
+		if ((miter->__flags & SG_MITER_TO_SG) &&
+		    !PageSlab(miter->page))
 			flush_kernel_dcache_page(miter->page);
 
 		if (miter->__flags & SG_MITER_ATOMIC) {

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