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Bug#349233: marked as done (apt: Segmentation faulty tree... 50%)

Your message dated Fri, 19 Aug 2011 12:05:22 +0200
with message-id <20110819115258.GA4040@debian.org>
and subject line Re: Bug#81829: "Segmentation faulty tree" (#270147) still present in Lenny, broken /var/cache/apt/*.bin available for download
has caused the Debian Bug report #81829,
regarding apt: Segmentation faulty tree... 50%
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

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-- 
81829: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=81829
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems
--- Begin Message --- 
Package: apt
Version: 0.6.43.2
Severity: grave

REASONING for grave

apt-get becomes unusable to the whole system. Can't install, remove or
query any information.

PROBLEM

Without any notice (under testing) apt-get stopped working and 
printing message

  Segmentation faulty tree... 50%

I've done some GOOGLING and it seems this bug has been seen before,
but no intelligent handling has been added to apt. See bug Bug#84277
where  Jason Gunthorpe <jgg@debian.org> writes:

    > apt-get segfaults w/out (in my opinion) any reason:

    This has always been traced back to file corruption in /var/cache/apt/*.bin

    If you can erase those files and run the apt command and have it work then
    that is definately the problem.

    Nobody has ever been able to reproduce it, unless they have buggy hardware
    :>

    Jason

This machine does not not have buggy hardware; apt has been working fine
from the start.

SUGGESTION:

As it seems that apt-get is able to start (and does not segfault),
would it be possible to add a signal handler or error handler that -
when encountering this problem - would print a messsage:

  Hm, I suspect corrupted data files. Please delete
  /var/cache/apt/*.bin followed by "apt-get update" to reset apt.

Which indeed fixed this error condition.

-- Package-specific info:

-- (no /etc/apt/preferences present) --


-- (/etc/apt/sources.list present, but not submitted) --


-- System Information:
Debian Release: testing/unstable
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'stable')
Architecture: i386 (i686)
Shell:  /bin/sh linked to /bin/dash
Kernel: Linux 2.6.14-2-686
Locale: LANG=C, LC_CTYPE=C (charmap=ISO-8859-1) (ignored: LC_ALL set to en_US)

Versions of packages apt depends on:
ii  libc6                         2.3.5-12   GNU C Library: Shared libraries an
ii  libgcc1                       1:4.0.2-7  GCC support library
ii  libstdc++6                    4.0.2-7    The GNU Standard C++ Library v3

Versions of packages apt recommends:
pn  debian-archive-keyring        <none>     (no description available)

-- no debconf information

--- End Message ---
--- Begin Message --- 
Source: apt
Source-Version: 0.8.16~exp4

apt (0.8.16~exp4) experimental; urgency=low

   [ Julian Andres Klode ]
   * apt-pkg/pkgcache.h:
     - [ABI break] Add pkgCache::Header::CacheFileSize, storing the cache size
   * apt-pkg/pkgcachegen.cc:
     - Write the file size to the cache
   * apt-pkg/pkgcache.cc:
     - Check that cache is at least CacheFileSize bytes large (LP: #16467)

On Thu, Aug 18, 2011 at 04:16:05PM -0500, Jonathan Nieder wrote:
> tags 81829 - moreinfo
> quit
> 
> Axel Beckert wrote:
> 
> > I occasionally ran into this bug on Lenny, can't remember on which
> > platform, but never deterministically.
> >
> > But today I reproducibly ran into this bug with both, apt-get and
> > aptitude. Independent of what I did: aptitude; aptitude -u; aptitude
> > upgrade; apt-get upgrade, I always get the "Segmentation faulty
> > tree... 50%" ("Building dependency tree... 50%^MSegmentation fault").
> >
> > Moving /var/lib/apt/extended_states away didn't help.
> >
> > Couldn't even do an apt-get install gdb for generating a backtrace.
> >
> > Moving away pkgcache.bin and srcpkgcache.bin from /var/cache/apt/
> > finally did help (thanks to waldi for that hint), but copying them
> > back after upgrading two packages didn't reproduce the segfault --
> > they always got recreated.
> 
> Thanks!  No promises about being able to take a look soon, but I've
> downloaded them.
I closed the Launchpad bug in 0.8.16~exp4, but forgot to close that 
one. We still cannot detect invalid caches where data changes, but we
can now detect all truncated caches, and reject them.

I could have included a CRC checksum in the header of the remaining
cache, but our experience so far is that 

 (a) most (all?) of these bugs are the result of truncated cache files
 (b) checksumming the cache on opening is much slower than we want,
     especially on ARM systems (200 ms on abel.d.o, 500 ms on an N900,
     12 ms on my Intel Core i5)

That said, if future shows us cases where there are problems with
correctly-sized caches, we can still add a checksum when we break
ABI again, and enable it by default only on amd64 and other fast
architectures.

-- 
Julian Andres Klode  - Debian Developer, Ubuntu Member

See http://wiki.debian.org/JulianAndresKlode and http://jak-linux.org/.

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