From: Jeff King <peff@peff.net>
To: "Randall S. Becker" <rsbecker@nexbridge.com>
Cc: Max Kirillov <max@max630.net>,
'Junio C Hamano' <gitster@pobox.com>,
git@vger.kernel.org
Subject: Re: [ANNOUNCE] Git v2.33.0-rc2 (Build/Test Report)
Date: Mon, 16 Aug 2021 17:55:01 -0400 [thread overview]
Message-ID: <YRretXfEfiVujSeO@coredump.intra.peff.net> (raw)
In-Reply-To: <01b901d792d0$1e993950$5bcbabf0$@nexbridge.com>
On Mon, Aug 16, 2021 at 02:54:14PM -0400, Randall S. Becker wrote:
> >That 60 seconds is the timeout from t5562/invoke-with-content-length.
> >
> >So one, are you sure it's hanging forever, and not just for 60 seconds?
>
> Absolutely sure. 48 hours because I forgot to check.
>
> >And two, it is quite obvious there's some racing here. I'm not sure if this is indicative of a problem in the test suite, or in http-backend
> >itself (in which case it could be affecting real users).
>
> How can I help track this down?
Here's what I found out so far. For my 60-second lag case, the test
_does_ complete as expected; it just takes a long time. So I think what
happens is this:
- the invoke-with-content-length script sets up a SIGCLD handler
- then it kicks off http-backend and writes to it
- then it sleeps for 60 seconds, assuming that SIGCLD will interrupt
the sleep
- after the sleep finishes (whether by 60 seconds or because it was
interrupted by the signal), we check a flag to see if our SIGCLD
handler was called. If not, then we complain.
This usually completes instantaneously-ish, because the signal
interrupts our sleep. But very occasionally the child process dies
_before_ we hit the sleep, so we don't realize it.
So ideally we'd have some way of atomically checking our flag and then
sleeping only if it's not set. But I don't think that exists. The
closest we can come is using a series of smaller sleeps and checks. And
indeed, digging in the archive shows that Max already proposed such a
patch:
https://lore.kernel.org/git/20190218205028.32486-1-max@max630.net/
It looks like it feel through the cracks, though. Maybe now is a good
time to resurrect it.
However, you are in that thread, too, and it didn't help your situation.
So I think your race is somehow different. It looks like there was some
weirdness around close() for you, though generally we _shouldn't_ be
hitting that close() at all, because we'd have gotten SIGCLD and set the
$exited flag in the interim.
-Peff
next prev parent reply other threads:[~2021-08-16 21:55 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-13 14:22 [ANNOUNCE] Git v2.33.0-rc2 (Build/Test Report) Randall S. Becker
2021-08-13 15:00 ` Junio C Hamano
2021-08-13 16:06 ` Jeff King
2021-08-16 18:08 ` Randall S. Becker
2021-08-16 18:35 ` Jeff King
2021-08-16 18:54 ` Randall S. Becker
2021-08-16 21:55 ` Jeff King [this message]
2021-08-16 21:59 ` Jeff King
2021-08-16 18:31 ` Randall S. Becker
2021-08-16 18:36 ` Jeff King
2021-08-16 20:43 ` Randall S. Becker
2021-08-16 21:02 ` Jeff King
2021-08-16 21:54 ` Randall S. Becker
2021-08-16 22:22 ` Jeff King
2021-08-16 22:29 ` Jeff King
2021-08-17 14:30 ` Randall S. Becker
2021-08-17 14:29 ` Randall S. Becker
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