Message-ID: <2a199ba7-1d18-438a-847e-5241b7dac514@gmail.com>
Date: Wed, 29 Apr 2026 21:00:00 +0300
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Subject: Re: Startup process deadlock: WaitForProcSignalBarriers vs aux
 process
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Andres Freund <andres@anarazel.de>,
 Matthias van de Meent <boekewurm+postgres@gmail.com>,
 Thomas Munro <thomas.munro@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Heikki Linnakangas <hlinnaka@iki.fi>
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 <CAD21AoBj+zKvgw_Q8gjr4YbKccW_uMe3OFQ5+KT246FHUuNXSQ@mail.gmail.com>
 <4358bd85-f6b4-4da6-9909-74428fe3c8f7@gmail.com>
 <CAD21AoBDjU4fi+QgaC7RimqrDoUi9Ma+oBP10i0Je13NPSYcuw@mail.gmail.com>
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From: Alexander Lakhin <exclusion@gmail.com>
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Dear Sawada-san,

28.04.2026 22:27, Masahiko Sawada wrote:
> On Mon, Apr 27, 2026 at 11:00 AM Alexander Lakhin <exclusion@gmail.com> wrote:
>> I've been puzzled by a buildfarm failure [1] with such symptoms for a while
>> and even reproduced it locally once, but couldn't gather more information
>> that time. But now that you have described the scenario, I can easily
>> reproduce the same test failure with:
>> --- a/src/backend/storage/ipc/procsignal.c
>> +++ b/src/backend/storage/ipc/procsignal.c
>> @@ -206,6 +206,7 @@ ProcSignalInit(const uint8 *cancel_key, int cancel_key_len)
>>          if (cancel_key_len > 0)
>>                  memcpy(slot->pss_cancel_key, cancel_key, cancel_key_len);
>>          slot->pss_cancel_key_len = cancel_key_len;
>> +pg_usleep(10000);
>>          pg_atomic_write_u32(&slot->pss_pid, MyProcPid);
> Thank you for testing this.
>
> I've attached a patch to address the issue. I haven't verified it
> across all versions yet, but I suspect it exists in the stable
> branches as well...

Thank you for the fix! It works for me too.

I was wondering why is that failure the only one of this kind on buildfarm
(in last two years, at least), so I've tried to reproduce it on
REL_18_STABLE... and failed.

Then I've bisected it on the master branch and found (your) commit that
introduced this behavior: 67c20979c from 2025-12-23.

Best regards,
Alexander