Re: Parallel worker hangs while handling errors.

On Fri, Aug 7, 2020 at 1:34 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Tue, Jul 28, 2020 at 5:35 AM Bharath Rupireddy
> <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
> > The v4 patch looks good to me. Hang is not seen, make check and make
> > check-world passes. I moved this to the committer for further review
> > in https://commitfest.postgresql.org/29/2636/.
>
> I don't think I agree with this approach. In particular, I don't
> understand the rationale for unblocking only SIGUSR1. Above, Vignesh
> says that he feels that unblocking only that signal would be the right
> approach, but no reason is given. I have two reasons why I suspect
> it's not the right approach. One, it doesn't seem to be what we do
> elsewhere; the only existing cases where we have special handling for
> particular signals are SIGQUIT and SIGPIPE, and those places have
> comments explaining the reason why they are handled in a special way.
>

We intend to unblock SIGQUIT before sigsetjmp() in places like
bgwriter, checkpointer, walwriter and walreceiver, but we only call
sigdelset(&BlockSig, SIGQUIT);, Without PG_SETMASK(&BlockSig);, seems
like we are not actually unblocking SIQUIT and quickdie() will never
get called in these processes if (sigsetjmp(local_sigjmp_buf, 1) !=
0){....}, if postmaster sends a SIGQUIT while these processes are
doing clean up tasks in sigsetjmp(), it will not be received, and the
postmaster later sends SIGKLL to kill from below places.

/*
* If we already sent SIGQUIT to children and they are slow to shut
* down, it's time to send them SIGKILL. This doesn't happen
* normally, but under certain conditions backends can get stuck while
* shutting down. This is a last measure to get them unwedged.
*
* Note we also do this during recovery from a process crash.
*/
if ((Shutdown >= ImmediateShutdown || (FatalError && !SendStop)) &&
AbortStartTime != 0 &&
(now - AbortStartTime) >= SIGKILL_CHILDREN_AFTER_SECS)
{
/* We were gentle with them before. Not anymore */
TerminateChildren(SIGKILL);
/* reset flag so we don't SIGKILL again */
AbortStartTime = 0;
}

Shouldn't we call PG_SETMASK(&BlockSig); to make it effective?

Am I missing anything here?

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com