linux-kernel - Re: Filesystem corruption MD (imsm) Raid0 via 2 SSD's + discard

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Date:	Thu, 21 May 2015 17:14:25 +1000
From:	NeilBrown <neilb@...e.de>
To:	Holger Kiehl <Holger.Kiehl@....de>
Cc:	Roman Mamedov <rm@...anrm.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-raid <linux-raid@...r.kernel.org>
Subject: Re: Filesystem corruption MD (imsm) Raid0 via 2 SSD's + discard

On Thu, 21 May 2015 06:44:27 +0000 (UTC) Holger Kiehl <Holger.Kiehl@....de>
wrote:

> On Thu, 21 May 2015, NeilBrown wrote:
> 
> > On Thu, 21 May 2015 01:32:13 +0500 Roman Mamedov <rm@...anrm.net> wrote:
> >
> >> On Wed, 20 May 2015 20:12:31 +0000 (UTC)
> >> Holger Kiehl <Holger.Kiehl@....de> wrote:
> >>
> >>> The kernel I was running when I discovered the
> >>> problem was 4.0.2 from kernel.org. However, after reinstalling from DVD
> >>> I updated to Fedora's lattest kernel, which was 3.19.? (I do not remember
> >>> the last numbers). So that kernel seems also effected, but I assume it
> >>> contains many 'fixes' from 4.0.x. As filesystem I use ext4, distribution
> >>> is Fedora 21 and hardware is: Xeon E3-1275, 16GB ECC Ram.
> >>>
> >>> My system seems to be now running stable for some days with kernel.org
> >>> kernel 4.0.3 and with discard DISABLED. But I am still unsure what could
> >>> be the real cause.
> >>
> >> It is a bug in the 4.0.2 kernel, fixed in 4.0.3.
> >>
> >> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=785672
> >> https://bbs.archlinux.org/viewtopic.php?id=197400
> >> https://kernel.googlesource.com/pub/scm/linux/kernel/git/stable/linux-stable/+/d2dc317d564a46dfc683978a2e5a4f91434e9711
> >>
> >>
> >
> > I suspect that is a different bug.
> > I think this one is
> >  https://bugzilla.kernel.org/show_bug.cgi?id=98501
> >
> Should there not be a big fat warning going around telling users to disable
> discard on Raid 0 until this is fixed? This breaks the filesystem completely
> and I believe there is absolutly no way one can get back the data.

Probably.  Would you like to do that?

> 
> Is this fixed in 4.0.4? And which kernels are effected? There could be many
> people running systems that have not noticed this and don't know in what
> dangerous situation they are when they delete data.

The patch was only added to my tree today.  I will send to Linus tomorrow so
it should appear in the next -rc.
Any -stable kernel released since mid-April probably has the bug.  It was
caused by
commit 47d68979cc968535cb87f3e5f2e6a3533ea48fbd

Once the fix gets into Linus' tree, it should get into subsequent -stable releases.

The fix is here:

http://git.neil.brown.name/?p=md.git;a=commitdiff;h=a81157768a00e8cf8a7b43b5ea5cac931262374f

commit id should remain unchanged.

Thanks,
NeilBrown


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