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From: Alexander Lakhin <[email protected]>
To: Masahiko Sawada <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: Matthias van de Meent <[email protected]>
Cc: Thomas Munro <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Subject: Re: Startup process deadlock: WaitForProcSignalBarriers vs aux process
Date: Wed, 29 Apr 2026 21:00:00 +0300
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAD21AoBDjU4fi+QgaC7RimqrDoUi9Ma+oBP10i0Je13NPSYcuw@mail.gmail.com>
References: <CAEze2WgAJmWReDN7Chtba8Er2YBvKCoa0KVN25-1evnTrHsLyA@mail.gmail.com>
	<ojnnvj553eber32njg5nphybcf6zvb3bzexfkh3obylsll67pc@jk7jmtzeb66k>
	<CAD21AoBj+zKvgw_Q8gjr4YbKccW_uMe3OFQ5+KT246FHUuNXSQ@mail.gmail.com>
	<[email protected]>
	<CAD21AoBDjU4fi+QgaC7RimqrDoUi9Ma+oBP10i0Je13NPSYcuw@mail.gmail.com>

Dear Sawada-san,

28.04.2026 22:27, Masahiko Sawada wrote:
> On Mon, Apr 27, 2026 at 11:00 AM Alexander Lakhin <[email protected]> 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

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