Re: plperl sigfpe reset can crash the server

On Friday, August 24, 2012 06:55:04 AM Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > On Thursday, August 23, 2012 12:17:22 PM Andres Freund wrote:
> >> While debugging an instance of this bug I noticed that plperlu always
> >
> >> removes the SIGFPE handler and sets it to ignore:
> > In fact it can be used to crash the server:
> Um ... how exactly can that happen, if the signal is now ignored?

Don't ask me the hard questions at 7 in the morning. I have no clue yet.

I don't see where but something resets SIGFPE before the server crashes. If I
catch the sigfpe with gdb I see:

test=# SELECT pg_backend_pid();
pg_backend_pid
----------------
18084

root(at)awork2:/home/andres# grep -E '^Sig(Cgt|Ign)' /proc/18084/status
SigIgn: 0000000001301800
SigCgt: 0000000180006287

test=# SELECT (-2^31)::int/-1;
ERROR: floating-point exception
DETAIL: An invalid floating-point operation was signaled. This probably means
an out-of-range result or an invalid operation, such as division by zero.

root(at)awork2:/home/andres# grep -E '^Sig(Cgt|Ign)' /proc/18084/status
SigIgn: 0000000001301800
SigCgt: 0000000180006287

test=# DO LANGUAGE plperl $$$$;

root(at)awork2:/home/andres# grep -E '^Sig(Cgt|Ign)' /proc/18084/status
SigIgn: 0000000001301880
SigCgt: 0000000180006207

test=# SELECT (-2^31)::int/-1;

Program received signal SIGFPE, Arithmetic exception.
0x00007f858001f8c6 in int4div (fcinfo=0x7f8581b30320)

root(at)awork2:/home/andres# grep -E '^Sig(Cgt|Ign)' /proc/18084/status
SigIgn: 0000000001301800
SigCgt: 0000000180006207

Andres
--
Andres Freund http://www.2ndQuadrant.com/
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