Re: BUG #16754: When using LLVM and parallel queries aborted all session by pg_cancel_backend.

On Thu, Jul 28, 2022 at 1:11 PM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> On Tue, Dec 8, 2020 at 4:35 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > On 2020-12-07 08:58:18 +0000, Shinoda, Noriyoshi (PN Japan FSIP) wrote:
> > > Thanks for the comment.
> > > I newly cloned the latest version 13.1 source and then rebuilt it. The
> > > segmentation fault has recurred.I tried the backtrace feature, but it
> > > didn't work.
> >
> > What exactly do you mean by that? You attached to the worker with a
> > debugger, and you didn't get a backtrace once it crashed? Same with a
> > core file? Or were you hoping for the segfault to automatically
> > generate a backtrace?
> >
> > The easist way would be to enable core files with 'ulimit -c unlimited'
> > in the shell you start postgres in, and to set the
> > 'jit_debugging_support=1' option. Then, once the crash happend, you
> > should be able to find a core file.
> >
> > You then can inspect that core file with
> > gdb /path/to/postgres -core /path/to/core
> >
> > and execute 'bt' inside.
> >
> >
> > > The function specification may not have been good.
> >
> > Which function's specification?
> >
> >
> > > Segmentation faults do not always occur, but occasionally after running pg_cancel_backend several times.
> > > Also, it only seems to happen if I canceled the parallel worker process.
> >
> > I tried this a couple hundred times without success.
>
> I have happened to run into an odd JIT-related crash that may be related.
>
> It happens (almost) every time when I run make installcheck with
> force_parallel_mode=regress and build with LLVM 7.0.

Forgot to mention: no crash when using LLVM 9.0 though.

--
Thanks, Amit Langote
EDB: http://www.enterprisedb.com