Seg Fault on git fetch with fetch.negotiationAlgorithm=skipping

Seg Fault on git fetch with fetch.negotiationAlgorithm=skipping

[Son Luong Ngoc]

Hi folks,

We recently encountered a segfault during a git fetch
strace output could be found https://gist.github.com/sluongng/e48327cc911c617ed2ef8578acc2ea34

The root cause was due to having `fetch.negotiationAlgorithm=skipping`
The repo is about linux.git size with a few NULL commit that we have been using `fsck.skipList` 
on both server and client side to skip.

Is this and edge case for the new algorithm?

Cheers,
Son Luong.

Re: Seg Fault on git fetch with fetch.negotiationAlgorithm=skipping

[Taylor Blau]

Hi Son,

On Thu, Apr 30, 2020 at 04:55:07PM +0200, Son Luong Ngoc wrote:
> Hi folks,
>
> We recently encountered a segfault during a git fetch
> strace output could be found https://gist.github.com/sluongng/e48327cc911c617ed2ef8578acc2ea34
>
> The root cause was due to having `fetch.negotiationAlgorithm=skipping`
> The repo is about linux.git size with a few NULL commit that we have been using `fsck.skipList`
> on both server and client side to skip.

Are you able to share a core file? If not, it would be very helpful for
you to 'git fast-export --anonymize ...' and see if you can reproduce
the problem on an anonymized copy of your repository.

I can speculate about the cause of the crash from your strace above, but
a core file would be more helpful.

> Is this and edge case for the new algorithm?
>
> Cheers,
> Son Luong.

Thanks,
Taylor

Re: Seg Fault on git fetch with fetch.negotiationAlgorithm=skipping

[Son Luong Ngoc]

Hi Taylor,

> On Apr 30, 2020, at 22:20, Taylor Blau <me@ttaylorr.com> wrote:
> 
> Are you able to share a core file? If not, it would be very helpful for
> you to 'git fast-export --anonymize ...' and see if you can reproduce
> the problem on an anonymized copy of your repository.

I played a bit with --anonymized yesterday but export/import is slow and I still need to review
the history to see whether it could be released.

It might take more time than just a few days.

> I can speculate about the cause of the crash from your strace above, but
> a core file would be more helpful.

I have added perf trace2 in https://gist.github.com/sluongng/e48327cc911c617ed2ef8578acc2ea34#file-perf-trace2-L52
(git version is 2.26.2)

I think this trace is a lot cleared than the strace log.

> Thanks,
> Taylor

Cheers,
Son Luong.

Re: Seg Fault on git fetch with fetch.negotiationAlgorithm=skipping

[Taylor Blau]

On Fri, May 01, 2020 at 10:13:43AM +0200, Son Luong Ngoc wrote:
> Hi Taylor,
>
> > On Apr 30, 2020, at 22:20, Taylor Blau <me@ttaylorr.com> wrote:
> >
> > Are you able to share a core file? If not, it would be very helpful for
> > you to 'git fast-export --anonymize ...' and see if you can reproduce
> > the problem on an anonymized copy of your repository.
>
> I played a bit with --anonymized yesterday but export/import is slow and I still need to review
> the history to see whether it could be released.
>
> It might take more time than just a few days.

That's OK. Please let us know when you have it by responding in the
sub-thread here, and I will be happy to take a look.

> > I can speculate about the cause of the crash from your strace above, but
> > a core file would be more helpful.
>
> I have added perf trace2 in https://gist.github.com/sluongng/e48327cc911c617ed2ef8578acc2ea34#file-perf-trace2-L52
> (git version is 2.26.2)
>
> I think this trace is a lot cleared than the strace log.
>
> > Thanks,
> > Taylor
>
> Cheers,
> Son Luong.

Thanks,
Taylor