Re: buildfarm instance bichir stuck

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Robins Tharakan <tharakan(at)gmail(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: buildfarm instance bichir stuck
Date: 2021-04-07 11:49:38
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On 4/7/21 2:16 AM, Thomas Munro wrote:
> On Wed, Apr 7, 2021 at 5:44 PM Robins Tharakan <tharakan(at)gmail(dot)com> wrote:
>> Bichir's been stuck for the past month and is unable to run regression tests since 6a2a70a02018d6362f9841cc2f499cc45405e86b.
> Hrmph. That's "Use signalfd(2) for epoll latches." I had a similar
> report from an illumos user (but it was intermittent). I have never
> seen such a failure on Linux. My first guess is that these two
> systems that are doing Linux system call emulation have implemented
> subtly different semantics, and something is going wrong like this: a
> SIGUSR1 arrives to tell you some important news about a procsignal and
> the signal handler calls SetLatch(MyLatch) which does kill(MyProcPid,
> SIGURG), but somehow that fails to wake up the epoll() you are
> sleeping in which contains the signalfd that should receive the signal
> and report it by being readable, due to some internal race. Or
> something like that. But I haven't been able to verify that theory
> because I don't have any of those computers. If it is indeed
> something like that and not a bug in my code, then I was thinking that
> the main tool available to deal with it would be to set WAIT_USE_POLL
> in the relevant template file, so that we don't use the combination of
> epoll + signalfd on illlumos, but then WSL1 thows a spanner in the
> works because AFAIK it's masquerading as Ubuntu, running PostgreSQL
> from an Ubuntu package with a freaky kernel. Hmm.

To test this the OP could just add


to his animal's config's config_env stanza.



Andrew Dunstan

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