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From: Vivek Goyal <vgoyal@redhat.com>
To: "misono.tomohiro@fujitsu.com" <misono.tomohiro@fujitsu.com>
Cc: "'virtio-fs@redhat.com'" <virtio-fs@redhat.com>,
	"'qemu-devel@nongnu.org'" <qemu-devel@nongnu.org>
Subject: Re: [Virtio-fs] [PATCH] virtiofsd: Fix data corruption with O_APPEND wirte in writeback mode
Date: Thu, 31 Oct 2019 11:47:10 -0400	[thread overview]
Message-ID: <20191031154710.GB7308@redhat.com> (raw)
In-Reply-To: <OSBPR01MB3783739E4F9545DABEF3E230E5630@OSBPR01MB3783.jpnprd01.prod.outlook.com>

On Thu, Oct 31, 2019 at 09:39:23AM +0000, misono.tomohiro@fujitsu.com wrote:
[..]
> > > > Hi Misono,
> > > >
> > > > Have you tried running pjdfstests. Looks like with the patch applied
> > > > I see following tests failing which were passing without the patch.
> > > > Can you please have a look. I ran daemon with options "-o
> > > cache=always -o writeback"
> > 
> > I see these errors in both with and without this patch but not always.
> > Do you always see the failure?
> > 
> > I use:
> >   Kernel: Fuse's for-next branch
> >   Qemu: virtio-fs-dev branch
> >   backend: XFS (relatime)
> > 
> > These tests fail because a/c/m time is not updated as expected.
> > So it seems this is related to the failure of xfstest generic/003.
> > I will look into the problem more.
> > 
> 
> Hi,
> 
> So I fugured out the problem. 
> The failure occurs when guest clock is earlier than host clock in writeback mode.
> 
> The failure case checks:
>  1. get current c/time of file
>  2. sleep 1 second
>  3. modify file's metadata/data
>  4. check if c/mtime is updated
> 
> And the tests fail because:
>  1. when file is opened, guest inode's time is initialized by host's inode information
>  2. In writeback mode, guest clock is used for c/mtime update
>  3. if guest clock is earlier than host clock, c/mtime could be updated
>     earlier than current inode time. 
> 
> I can reproduce the problem reliably by deliberately setting guest clock earlier
> than host clock. I'm not sure if virtiofs is to be blmaed in this case, but should
> we not update c/mtime in guest if it is earlier then current c/mtime?
> 
> Anyway, I believe this O_APPEND fix patch is irrelevant to the problem,
> could you please check it again?

Hi Misono,

Thanks for looking into it. I agree that a/c/m time updates with -o writeback
is probably a different issue and not related to your patch. So I am fine
with your patch.

Thanks
Vivek



  reply	other threads:[~2019-10-31 15:59 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-23 12:25 Misono Tomohiro
2019-10-23 20:07 ` [Virtio-fs] " Vivek Goyal
2019-10-24 15:02   ` Vivek Goyal
2019-10-25 10:02     ` misono.tomohiro
2019-10-29 10:07       ` misono.tomohiro
2019-10-31  9:39         ` misono.tomohiro
2019-10-31 15:47           ` Vivek Goyal [this message]
2019-10-31 15:47 ` Vivek Goyal
2019-11-01  8:08   ` Dr. David Alan Gilbert

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