Re: [PATCH] fetch-pack: ignore SIGPIPE when writing to index-pack

From: Jeff King <peff@peff.net>
Date: Nov 19, 2021, 22:32 UTC
Message-ID: <YZgl5qYbAyAsixmo@coredump.intra.peff.net>
In-Reply-To: <xmqqy25jokft.fsf@gitster.g>

On Fri, Nov 19, 2021 at 02:21:58PM -0800, Junio C Hamano wrote:

Show 14 quoted lines

> Jeff King <peff@peff.net> writes:
> 
> > When fetching, we send the incoming pack to index-pack (or
> > unpack-objects) via the sideband demuxer. If index-pack hits an error
> > (e.g., because an object fails fsck), then it will die immediately. This
> > may cause us to get SIGPIPE on the fetch, as we're still trying to write
> > pack contents from the sideband demuxer (which is typically a thread,
> > and thus takes down the whole fetch process).
> 
> So, ... we'd die anyway and won't update the refs and anything that
> leaves permanent damage to the repository either way, but we choose
> a better way to die by not taking SIGPIPE, but to get an error from
> one of the write()s or the final close(), which will lead us to more
> "controlled" death using the normal error path?

Yes, exactly. We'll be exiting either way; it's just a matter of racily changing the exit code and possibly the error message from the parent fetch process.

So I do doubt this really hurts users much in practice, but making the tests robust seems worth it to me (because I found it after tracking down a flaky test failure). And because it _is_ a race in the code, I fixed it there rather than papering over the SIGPIPE exit in the test script.

-Peff