[3.5.y.z extended stable] Patch "lib/scatterlist.c: don't flush_kernel_dcache_page on slab page" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Tue Nov 12 12:45:44 UTC 2013

This is a note to let you know that I have just added a patch titled

    lib/scatterlist.c: don't flush_kernel_dcache_page on slab page

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From 0723a210c747c37a65f951f8f4c2d3635779f867 Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei at canonical.com>
Date: Thu, 31 Oct 2013 16:34:17 -0700
Subject: lib/scatterlist.c: don't flush_kernel_dcache_page on slab page

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

 - 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 at canonical.com>
Reported-by: Aaro Koskinen <aaro.koskinen at iki.fi>
Tested-by: Simon Baatz <gmbnomis at gmail.com>
Cc: Russell King - ARM Linux <linux at arm.linux.org.uk>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Aaro Koskinen <aaro.koskinen at iki.fi>
Acked-by: Catalin Marinas <catalin.marinas at arm.com>
Cc: FUJITA Tomonori <fujita.tomonori at lab.ntt.co.jp>
Cc: Tejun Heo <tj at kernel.org>
Cc: "James E.J. Bottomley" <JBottomley at parallels.com>
Cc: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 lib/scatterlist.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 6096e89..8c2f278 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -419,7 +419,8 @@ void sg_miter_stop(struct sg_mapping_iter *miter)
 	if (miter->addr) {
 		miter->__offset += miter->consumed;

-		if (miter->__flags & SG_MITER_TO_SG)
+		if ((miter->__flags & SG_MITER_TO_SG) &&
+		    !PageSlab(miter->page))

 		if (miter->__flags & SG_MITER_ATOMIC) {

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