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

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 <[email protected]>
Reported-by: Aaro Koskinen <[email protected]>
Tested-by: Simon Baatz <[email protected]>
Cc: Russell King - ARM Linux <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Aaro Koskinen <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Cc: FUJITA Tomonori <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: <[email protected]>	[3.2+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions