NULL characters in file on ReiserFS again.

NULL characters in file on ReiserFS again.

[Andrej Borsenkow]

This happened to me yesterday on kernel-2.4.4-6mdk (Mandrake cooker, based
on 2.4.4-ac14), single reiser root filesystem, mounted with default options.
Hardware - ASUS CUSL2 (i815e chipset), Fujitsu UDMA-4 drive.

I tried to change hostname and did not have the corresponding entry in
/etc/hosts (or anywhere). As a tesult, startx hung starting X server; it was
not possible to switch to alpha console or kill X server. I pressed reset
and after reboot looked into /var/log/XFree86*log - and there were a bunch
of ^@ there.

I then run fsck from another system (installed on another partition) but
there was no errors (well, new errors - there was off-by-one free blocks
bitmap mismatch but it was always there, I do not know how to correct it). I
tried the above once more but this time XFree log was O.K.

So, I really do not know how to reproduce it, but I wanted to give a warning
that a problem still exists (albeit in emergency situation). As Reiser does
not do any fsck after crash, the problem is serious enough IMHO.

-andrej

Re: NULL characters in file on ReiserFS again.

[Chris Mason]

On Thursday, May 31, 2001 03:33:06 PM +0400 Andrej Borsenkow
<Andrej.Borsenkow@mow.siemens.ru> wrote:

> This happened to me yesterday on kernel-2.4.4-6mdk (Mandrake cooker, based
> on 2.4.4-ac14), single reiser root filesystem, mounted with default
> options. Hardware - ASUS CUSL2 (i815e chipset), Fujitsu UDMA-4 drive.
> 
> I tried to change hostname and did not have the corresponding entry in
> /etc/hosts (or anywhere). As a tesult, startx hung starting X server; it
> was not possible to switch to alpha console or kill X server. I pressed
> reset and after reboot looked into /var/log/XFree86*log - and there were
> a bunch of ^@ there.
> 

There are two ways to get nulls in log files.  reiserfs bugs, and a crash
before data blocks are flushed to disk.  You've probably hit the second.
Reiserfs only logs metadata, so it is possible for newly allocated data
blocks to have null bytes after a crash.

Patches are in progress to flush new data blocks before transaction commit.
I'm about to send out the first building block for this...

-chris

Re: NULL characters in file on ReiserFS again.

[Hans Reiser]

Andrej Borsenkow wrote:
> 
> This happened to me yesterday on kernel-2.4.4-6mdk (Mandrake cooker, based
> on 2.4.4-ac14), single reiser root filesystem, mounted with default options.
> Hardware - ASUS CUSL2 (i815e chipset), Fujitsu UDMA-4 drive.
> 
> I tried to change hostname and did not have the corresponding entry in
> /etc/hosts (or anywhere). As a tesult, startx hung starting X server; it was
> not possible to switch to alpha console or kill X server. I pressed reset
> and after reboot looked into /var/log/XFree86*log - and there were a bunch
> of ^@ there.
> 
> I then run fsck from another system (installed on another partition) but
> there was no errors (well, new errors - there was off-by-one free blocks
> bitmap mismatch but it was always there, I do not know how to correct it). I
> tried the above once more but this time XFree log was O.K.
> 
> So, I really do not know how to reproduce it, but I wanted to give a warning
> that a problem still exists (albeit in emergency situation). As Reiser does
> not do any fsck after crash, the problem is serious enough IMHO.
> 
> -andrej
> 
> -
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> Please read the FAQ at  http://www.tux.org/lkml/
this is the nature of metadata journaling filesystems.

Re: NULL characters in file on ReiserFS again.

[Stephen C. Tweedie]

Hi,

On Thu, May 31, 2001 at 09:57:51AM -0700, Hans Reiser wrote:

> > /etc/hosts (or anywhere). As a tesult, startx hung starting X server; it was
> > not possible to switch to alpha console or kill X server. I pressed reset
> > and after reboot looked into /var/log/XFree86*log - and there were a bunch
> > of ^@ there.

> this is the nature of metadata journaling filesystems.

Umm, no, it isn't.  Ext3 would never allow that to happen in ordered
metadata-journaling mode, and Chris Mason is already working to remove
that window in reiserfs.  It is by no means a necessary consequence of
doing metadata-only journaling.

--Stephen

Re: NULL characters in file on ReiserFS again.

[Eric W. Biederman]

"Stephen C. Tweedie" <sct@redhat.com> writes:

> Hi,
> 
> On Thu, May 31, 2001 at 09:57:51AM -0700, Hans Reiser wrote:
> 
> > > /etc/hosts (or anywhere). As a tesult, startx hung starting X server; it was
> 
> > > not possible to switch to alpha console or kill X server. I pressed reset
> > > and after reboot looked into /var/log/XFree86*log - and there were a bunch
> > > of ^@ there.
> 
> > this is the nature of metadata journaling filesystems.
> 
> Umm, no, it isn't.  Ext3 would never allow that to happen in ordered
> metadata-journaling mode, and Chris Mason is already working to remove
> that window in reiserfs.  It is by no means a necessary consequence of
> doing metadata-only journaling.

Hans seemed to be refering to the fact that fsck.reiser returned
without errors on the partition being looked at.  Which is the nature
of metadata journalling.  The filesystem doesn't get corrupted though
the files might. 

Eric

Re: NULL characters in file on ReiserFS again.

[Tor Arntsen]

On Thu, May 31, 2001 at 09:57:51AM -0700, Hans Reiser wrote:
>Andrej Borsenkow wrote:
> > /etc/hosts (or anywhere). As a tesult, startx hung starting X server; it was
> > not possible to switch to alpha console or kill X server. I pressed reset
> > and after reboot looked into /var/log/XFree86*log - and there were a bunch
> > of ^@ there.

> this is the nature of metadata journaling filesystems.

Exactly the same thing happens on XFS filesystems on IRIX 6.5.
We had a bunch of Origin systems that crashed every so often because
of some PCI bus problems, and every time this happened every file
on the system that had been updated the last seconds before the
crash would be full of, or almost full of ^@.  Needless to say
this created havoc with CVS repositories and also checked-out
trees, since the CVS/Entries files would end up modified.

I first noticed this when my setiathome status files were empty
after the restarts.. *every* time.  I had to install a cron job 
that copied the status file every two minutes or so, the slightly
older copy would be okay so I could just copy it back after the
restart.

That was a nuisance, but when the CVS systems got wrecked it became
a little worse.  Obviously we have backups, but the problem was that
you wouldn't necessarily notice right away that anything was screwed.

Hopefully SGI will fix it, or maybe they have fixed it already -- 
I don't know.  I'm running 6.5.8 which isn't the latest (IRIX is
at 6.5.11 or 6.5.12 now I think), and it certainly wasn't fixed there.
If not, then XFS will never run on my Linux boxes, and certainly
not on the big Linux server that now holds our CVS repositories
instead of the SGI Origin system that we originally used :-)

In another posting Stephen Tweedie writes:
>Umm, no, it isn't.  Ext3 would never allow that to happen in ordered
>metadata-journaling mode, and Chris Mason is already working to remove
>that window in reiserfs.  It is by no means a necessary consequence of
>doing metadata-only journaling.

That's good news.

-Tor