Re: 4.7.0-rc7 ext4 error in dx_probe

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Aug 05, 2016 at 12:35:44PM +0200, Johannes Stezenbach wrote:
> On Wed, Aug 03, 2016 at 05:50:26PM +0300, Török Edwin wrote:
> > I have just encountered a similar problem after I've recently upgraded to 4.7.0:
> > [Wed Aug  3 11:08:57 2016] EXT4-fs error (device dm-1): dx_probe:740: inode #13295: comm python: Directory index failed checksum
> > [Wed Aug  3 11:08:57 2016] Aborting journal on device dm-1-8.
> > [Wed Aug  3 11:08:57 2016] EXT4-fs (dm-1): Remounting filesystem read-only
> > [Wed Aug  3 11:08:57 2016] EXT4-fs error (device dm-1): ext4_journal_check_start:56: Detected aborted journal
> > 
> > I've rebooted in single-user mode, fsck fixed the filesystem, and rebooted, filesystem is rw again now.
> > 
> > inode #13295 seems to be this and I can list it now:
> > stat /usr/lib64/python3.4/site-packages
> >   File: '/usr/lib64/python3.4/site-packages'
> >   Size: 12288     	Blocks: 24         IO Block: 4096   directory
> > Device: fd01h/64769d	Inode: 13295       Links: 180
> > Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
> > Access: 2016-05-09 11:29:44.056661988 +0300
> > Modify: 2016-08-01 00:34:24.029779875 +0300
> > Change: 2016-08-01 00:34:24.029779875 +0300
> >  Birth: -
> > 
> > The filesystem was /, I only noticed it was readonly after several hours when I tried to install something:
> > /dev/mapper/vg--ssd-root on / type ext4 (rw,noatime,errors=remount-ro,data=ordered)
> > 
> > $ uname -a
> > Linux bolt 4.7.0-gentoo-rr #1 SMP Thu Jul 28 11:28:56 EEST 2016 x86_64 AMD FX(tm)-8350 Eight-Core Processor AuthenticAMD GNU/Linux
> > 
> > FWIW I've been using ext4 for years and this is the first time I see this message.
> > Prior to 4.7 I was on 4.6.1 -> 4.6.2 -> 4.6.3 -> 4.6.4.
> > 
> > The kernel is from gentoo-sources + a patch for enabling AMD LWP (I had that patch since 4.6.3 and its not related to I/O).
> > 
> > If I see this message again what should I do to obtain more information to trace down the root cause?
> 
> It just happened again to me, this time hitting /usr/sbin/
> on root fs.  Meanwhile I ran memtest86 7.0 for two nights,
> it didn't find anything.  I'm using hibernate regularly
> and I think so this only happened after a few hibernate/resume
> cycles, but no idea if that means anything.
> Now I'm back at 4.4.16 to see if it reproduces.

When you're back on 4.7, can you apply this patch[1] to see if it fixes
the problem?  I speculate that the new parallel dir lookup code enables
multiple threads to be verifying the same directory block buffer at the
same time.

--D

[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/fs/ext4/inode.c?id=b47820edd1634dc1208f9212b7ecfb4230610a23

> 
> Johannes
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