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

[Catalin Marinas]

On Mon, Oct 28, 2013 at 04:20:05PM +0000, Ming Lei wrote:
> 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().
> 
> Reported-by: Aaro Koskinen <aaro.koskinen at iki.fi>
> Cc: Russell King - ARM Linux <linux at arm.linux.org.uk>
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: Simon Baatz <gmbnomis at gmail.com>
> Cc: Will Deacon <will.deacon at arm.com>
> Cc: Aaro Koskinen <aaro.koskinen at iki.fi>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> 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: Ming Lei <ming.lei at canonical.com>

Acked-by: Catalin Marinas <catalin.marinas at arm.com>