Re: OSTree locking fails sometimes

[Stefan Agner <stefan agner ch>]

On 24.01.2019 13:51, Dan Nicholson wrote:
> On Thu, Jan 24, 2019 at 3:41 AM Colin Walters <walters verbum org> wrote:
> > On Mon, Jan 14, 2019, at 12:16 PM, Stefan Agner wrote:
> > > Hello,
> >
> > [Hi, sorry about not replying earlier]
> >
> > > And get this every now and then:
> > > "error: Locking repo exclusive failed: Resource temporarily unavailable"
> >
> > Hmm.  So this boils down to do_repo_lock() which calls:
> >
> > res = TEMP_FAILURE_RETRY (fcntl (fd, (flags & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW, &fl));
> >
> > "Resource temporarily unavailable" maps to EAGAIN.
>
> That's the same as EWOULDBLOCK, which suggests there's lock contention
> and it times out. I'd guess that the more likely issue is the recent
> change to make summary generation take an exclusive lock in
> https://github.com/ostreedev/ostree/pull/1681. We discussed this when
> it started affecting one of our systems in
> https://github.com/endlessm/eos-updater/pull/237#issuecomment-425563031.
>
> But then he says that the processes are serialized...

We have about 6 builds which run in parallel and write into the same
OSTree at one point during the end of the build. bitbake should
serialize them, and in a dry run the serialization seems to work fine
across the NFS.

So I am not sure really who is to blame.


> Stefan, if you can run ostree with --verbose, then you'll get some
> more information about what's going on with the locking. My guess is
> that you're failing to exclusively lock the repo, but it would say in
> the debug messages.

Will add --verbose so we have better debug messages next time.

--
Stefan

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