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Date:	Thu, 26 Dec 2013 17:51:44 -0500
From:	Milosz Tanski <milosz@...in.com>
To:	Li Wang <liwang@...ntukylin.com>
Cc:	ceph-devel <ceph-devel@...r.kernel.org>,
	Sage Weil <sage@...tank.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	linux-kernel@...r.kernel.org,
	Yunchuan Wen <yunchuanwen@...ntukylin.com>
Subject: Re: [PATCH 0/3] Ceph fscache: Fix kernel panic due to a race

Li,

I looked at the patchset am I correct that this only happens when we
enable caching in the write path?

- Milosz

On Thu, Dec 26, 2013 at 9:29 AM, Li Wang <liwang@...ntukylin.com> wrote:
> From: Yunchuan Wen <yunchuanwen@...ntukylin.com>
>
> The following scripts could easily panic the kernel,
>
> #!/bin/bash
> mount -t ceph -o fsc MONADDR:/ cephfs
> rm -rf cephfs/foo
> dd if=/dev/zero of=cephfs/foo bs=8 count=512
> echo 3 > /proc/sys/vm/drop_caches
> dd if=cephfs/foo of=/dev/null bs=8 count=1024
>
> This is due to when writing a page into fscache, the code will
> assert that the write position does not exceed the
> object->store_limit_l, which is supposed to be equal to inode->i_size.
> However, for current implementation, after file writing, the
> object->store_limit_l is not synchronized with new
> inode->i_size immediately, which introduces a race that if writing
> a new page into fscache, will reach the ASSERT that write position
> has exceeded the object->store_limit_l, and cause kernel panic.
> This patch fixes it.
>
> Yunchuan Wen (3):
>   Ceph fscache: Add an interface to synchronize object store limit
>   Ceph fscache: Update object store limit after writing
>   Ceph fscache: Wait for completion of object initialization
>
>  fs/ceph/cache.c |    1 +
>  fs/ceph/cache.h |   10 ++++++++++
>  fs/ceph/file.c  |    3 +++
>  3 files changed, 14 insertions(+)
>
> --
> 1.7.9.5
>



-- 
Milosz Tanski
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p: 646-253-9055
e: milosz@...in.com
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