Re: Strange behavior (possible bugs) in btrfs

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Hi Filipe,

This is to follow up the status of crash consistency bugs we reported
on btrfs. We see that there has been a patch(not in the kernel yet)
(https://www.mail-archive.com/linux-btrfs@xxxxxxxxxxxxxxx/msg77875.html)
that resolves one of the reported bugs. However, the other bugs we
reported still exist on the latest kernel (4.19-rc1), even with the
submitted patch. Here is the list of other inconsistencies we
reported, along with the workload to reproduce them :
https://www.spinics.net/lists/linux-btrfs/msg77219.html

We just wanted to ensure that resolving these are on your to-do list.
Additionally, if there are more patches queued to address these
issues, please let us know.

Thanks,
Jayashree Mohan

Thanks,
Jayashree Mohan



On Fri, May 11, 2018 at 10:45 AM Filipe Manana <fdmanana@xxxxxxxxx> wrote:
>
> On Mon, Apr 30, 2018 at 5:04 PM, Vijay Chidambaram <vvijay03@xxxxxxxxx> wrote:
> > Hi,
> >
> > We found two more cases where the btrfs behavior is a little strange.
> > In one case, an fsync-ed file goes missing after a crash. In the
> > other, a renamed file shows up in both directories after a crash.
> >
> > Workload 1:
> >
> > mkdir A
> > mkdir B
> > mkdir A/C
> > creat B/foo
> > fsync B/foo
> > link B/foo A/C/foo
> > fsync A
> > -- crash --
> >
> > Expected state after recovery:
> > B B/foo A A/C exist
> >
> > What we find:
> > Only B B/foo exist
> >
> > A is lost even after explicit fsync to A.
> >
> > Workload 2:
> >
> > mkdir A
> > mkdir A/C
> > rename A/C B
> > touch B/bar
> > fsync B/bar
> > rename B/bar A/bar
> > rename A B (replacing B with A at this point)
> > fsync B/bar
> > -- crash --
> >
> > Expected contents after recovery:
> > A/bar
> >
> > What we find after recovery:
> > A/bar
> > B/bar
> >
> > We think this breaks rename's atomicity guarantee. bar should be
> > present in either A or B, but now it is present in both.
>
> I'll take a look at these, and all the other potential issues you
> reported in other threads, next week and let you know.
> Thanks.
>
> >
> > Thanks,
> > Vijay
> > --
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>
>
>
> --
> Filipe David Manana,
>
> “Whether you think you can, or you think you can't — you're right.”




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