Re: Crash after a call to pg_backup_start()

On Fri, Oct 21, 2022 at 7:06 PM Michael Paquier <michael@paquier.xyz> wrote:
>
> On Fri, Oct 21, 2022 at 05:53:25PM +0800, Richard Guo wrote:
> > Yeah, the two conditions could be both false. How about we update the
> > comment a bit to emphasize this? Such as
> >
> >     /* At most one of these conditions can be true */
> > or
> >     /* These conditions can not be both true */
>
> If you do that, it would be a bit easier to read as of the following
> assertion instead?  Like:
> Assert(!during_backup_start ||
>        sessionBackupState == SESSION_BACKUP_NONE);
>
> Please note that I have not checked in details all the interactions
> behind register_persistent_abort_backup_handler() before entering in
> do_pg_backup_start() and the ERROR_CLEANUP block used in this
> routine (just a matter of some elog(ERROR)s put here and there, for
> example).  Anyway, yes, both conditions can be false, and that's easy
> to reproduce:
> 1) Do pg_backup_start().
> 2) Do pg_backup_stop().
> 3) Stop the session to kick do_pg_abort_backup()
> 4) Assert()-boom.

I'm wondering if we need the assertion at all. We know that when the
arg is true or the sessionBackupState is SESSION_BACKUP_RUNNING, the
runningBackups would've been incremented and we can just go ahead and
decrement it, like the attached patch. This is a cleaner approach IMO
unless I'm missing something here.

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com