[PATCH 3.8 90/91] lib/scatterlist.c: don't flush_kernel_dcache_page on slab page

[Kamal Mostafa]

3.8.13.13 -stable review patch.  If anyone has any objections, please let me know.

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

From: Ming Lei <ming.lei@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
Reported-by: Aaro Koskinen <aaro.koskinen@xxxxxx>
Tested-by: Simon Baatz <gmbnomis@xxxxxxxxx>
Cc: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Aaro Koskinen <aaro.koskinen@xxxxxx>
Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: "James E.J. Bottomley" <JBottomley@xxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
 lib/scatterlist.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 7874b01..bd86887 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -495,7 +495,8 @@ 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))
 			flush_kernel_dcache_page(miter->page);
 
 		if (miter->__flags & SG_MITER_ATOMIC) {
-- 
1.8.1.2

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