Re: [PATCH] lib/scatterlist.c: don't flush_kernel_dcache_page onslab page

From: Andrew Morton
Date: Thu Oct 31 2013 - 18:27:50 EST

On Tue, 29 Oct 2013 00:20:05 +0800 Ming Lei <ming.lei@xxxxxxxxxxxxx> 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().

We should work out which kernel(s) need this patch. b1adaf65ba03 was
merged in 2008, so presumably some more recent patch has exposed the
problem, but I don't know what one that was.

Help me out here?
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