lib/scatterlist.c: don't flush_kernel_dcache_page on slab page
Ming Lei [Thu, 31 Oct 2013 23:34:17 +0000 (16:34 -0700)]
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 <>
Reported-by: Aaro Koskinen <>
Tested-by: Simon Baatz <>
Cc: Russell King - ARM Linux <>
Cc: Will Deacon <>
Cc: Aaro Koskinen <>
Acked-by: Catalin Marinas <>
Cc: FUJITA Tomonori <>
Cc: Tejun Heo <>
Cc: "James E.J. Bottomley" <>
Cc: Jens Axboe <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>


index a1cf8ca..3e7df38 100644 (file)
@@ -529,7 +529,8 @@ void sg_miter_stop(struct sg_mapping_iter *miter)
                miter->__offset += miter->consumed;
                miter->__remaining -= 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) {