[OpenAFS] Git throwing bus error when pack files not entirely cached

Michael La lass@mail.upb.de
Sun, 13 Mar 2016 21:39:05 +0100


Hi,

while trying to stress test the proposed patches for Linux 4.4 I
encountered an issue using git inside AFS that is not connected to the
Linux 4.4 issue:

I cloned the Linux kernel repo inside AFS. On this freshly cloned repo,
all data is stored in a single .pack file (.git/objects/pack/pack-
somehash.pack) that is about 1GB of size. When checking out revisions
of this repository, git almost always aborts with a bus error and
leaves the working copy in a broken state. This happens at different
stages of the checkout and only in rare cases the checkout finishes
without an error.

Now here's the interesting part: If the OpenAFS cache is large enough
and the pack file is entirely cached (e.g. by running "cat
.git/objects/pack/pack-somehash.pack > /dev/null" before) the errors
disappear completely. After flushing the cache (fs flushall) they
reappear. The smaller the cache size, the more often the errors seem to
occur.

I repeatedly built a checksum of the pack file unter different
circumstances and the checksum was always identical, so only git seems
to see a problem here.

File server versions tested:
- 1.6.9-2+deb8u4 from Debian Stable (Jessie)
- 1.6.15 from Debian Sid, running on Jessie

Client versions tested:
- 1.6.9-2+deb8u4 from Debian Jessie
- 1.6.15-1 from Debian Sid, running on Jessie
- 1.6.16 + proposed Linux-4.4 patches on Arch Linux

Git versions tested:
- 2.1.4-2.1+deb8u1 on Debian Jessie
- 2.7.2 on Arch Linux

Has this problem been observed before? Anything I can test to track
this down? It's at least easily reproducible.

Cheers,
Michael