| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Cc: | Marko Kreen <markokr(at)gmail(dot)com>, Postgres Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: 8.3.5: Crash in CountActiveBackends() - lockless race? |
| Date: | 2009-03-30 14:18:29 |
| Message-ID: | 3072.1238422709@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> Marko Kreen wrote:
>> Without reset in ProcArrayRemove we may use some ancient pointer that
>> may point to garbage? I don't think it's good coding style to allow
>> that to happen.
> Well, that can happen anyway. CountActiveBackends() could fetch the
> pointer and determine that it's not NULL, just before ProcArrayRemove
> clears it.
Dead PGPROC entries are just put into a list for reuse, so the pointer
would still point at storage that looked like a PGPROC. I concur with
Heikki's theory that the observed crash must have been from fetching a
pointer that was never yet not NULL.
regards, tom lane
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