Date: Thu, 31 Oct 2013 22:44:31 +0000
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Ming Lei <ming.lei@canonical.com>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, Simon Baatz <gmbnomis@gmail.com>,
        Will Deacon <will.deacon@arm.com>,
        Aaro Koskinen <aaro.koskinen@iki.fi>,
        Catalin Marinas <catalin.marinas@arm.com>,
        FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
        Tejun Heo <tj@kernel.org>,
        "James E.J. Bottomley" <JBottomley@parallels.com>,
        Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH] lib/scatterlist.c: don't flush_kernel_dcache_page on
	slab page
Message-ID: <20131031224431.GI16735@n2100.arm.linux.org.uk>
References: <1382977205-26268-1-git-send-email-ming.lei@canonical.com> <20131031152745.821d2b5dbe93e2ca69d45264@linux-foundation.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20131031152745.821d2b5dbe93e2ca69d45264@linux-foundation.org>
User-Agent: Mutt/1.5.19 (2009-01-05)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1794
Lines: 42

On Thu, Oct 31, 2013 at 03:27:45PM -0700, Andrew Morton wrote:
> On Tue, 29 Oct 2013 00:20:05 +0800 Ming Lei <ming.lei@canonical.com> 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?

1bc39742aab0 (ARM: 7755/1: handle user space mapped pages in
flush_kernel_dcache_page) in June 2013, which according to git describe
is:

v3.10-rc4-9-g1bc39742aab0

Presumably that means v3.10+ need it.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/