Horton

Re: SIGQUIT handling, redux

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2023-08-02T16:25:50Z
Lists: pgsql-hackers 
Hi,

On 2020-09-11 11:52:55 -0400, Tom Lane wrote:
> It's simple enough that maybe we could back-patch it, once it's
> aged awhile in HEAD.  OTOH, given the lack of field reports of
> trouble here, I'm not sure back-patching is worth the risk.

FWIW, looking at collected stack traces in azure, there's a slow but steady
stream of crashes below StartupPacketTimeoutHandler. Most seem to be things
like
libcrypto->malloc->StartupPacketTimeoutHandler->proc_exit->socket_close->free->crash
there's a few other variants, some where the stack apparently was not
decipherable for the relevant tooling.

Note that this wouldn't even include cases where this caused hangs - which is
quite common IME.


Unsurprisingly just in versions before 14, where this change went in.

I think that might be enough evidence for backpatching the commit? I've not
heard of issues due to the checks in check_on_shmem_exit_lists_are_empty().

Greetings,

Andres Freund

Commits

  1. Log a message when resorting to SIGKILL during shutdown/crash recovery.

  2. Don't run atexit callbacks during signal exits from ProcessStartupPacket.

  3. Use _exit(2) for SIGQUIT during ProcessStartupPacket, too.

  4. Make archiver's SIGQUIT handler exit via _exit().