Public repro case! Re: [PATCH/RFC] Allow writing loose objects that are corrupted in a pack file

On Wed, 2009-01-07 at 15:29 -0800, Linus Torvalds wrote:

It is certainly possible. It's too bad that it's private, because it makes 
it _much_ harder to try to pinpoint this.

My most esteemed colleague (Ken aka kb) who pointed out the memory issue
was on the right path (I think), and I have a reproduction case you can
try with your very own Linux kernel tree!

WOO!

I set ulimit -v really low (150M), and the operations I made got an
mmap(2) fatal error, but there is a sweet spot that I found, see the
transcript below. I basically chose an arbitrary revision from a couple
of weeks ago, and rolled the repository back to that point, then I tried
with iterations of ulimit -v 150, 250, 450, and then back down to 350.

        tyler@grapefruit:~/source/git/linux-2.6> limit
        cputime         unlimited
        filesize        unlimited
        datasize        unlimited
        stacksize       8MB
        coredumpsize    0kB
        memoryuse       2561MB
        maxproc         24564
        descriptors     1024
        memorylocked    64kB
        addressspace    unlimited
        maxfilelocks    unlimited
        sigpending      24564
        msgqueue        819200
        nice            0
        rt_priority     0
        tyler@grapefruit:~/source/git/linux-2.6> export
        START=56d18e9932ebf4e8eca42d2ce509450e6c9c1666
        tyler@grapefruit:~/source/git/linux-2.6> git reset --hard $START
        HEAD is now at 56d18e9 Merge branch 'upstream' of
        git://ftp.linux-mips.org/pub/scm/upstream-linus
        tyler@grapefruit:~/source/git/linux-2.6> ulimit -v `echo "350 *
        1024" | bc -l`
        tyler@grapefruit:~/source/git/linux-2.6> git pull
        error: failed to read object
        be1b87c70af69acfadb8a27a7a76dfb61de92643 at offset 1850923
        from .git/objects/pack/pack-dbe154052997a05499eb6b4fd90b924da68e799a.pack
        fatal: object be1b87c70af69acfadb8a27a7a76dfb61de92643 is
        corrupted
        tyler@grapefruit:~/source/git/linux-2.6>
        
I've tried this a couple of times, and it does seem to be reproducible,
let me know if you have any issues reproducing it locally and I'll try
to dig into it more with valgrind or something a bit more pin-pointing
than "ulimit -v && try, try again"


Cheers
-- 
-R. Tyler Ballance
Slide, Inc.