Re: BUG #12918: Segfault in BackendIdGetTransactionIds

* Vladimir Borodin (root(at)simply(dot)name) wrote:
>
> > 30 марта 2015 г., в 19:33, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> написал(а):
> >
> > root(at)simply(dot)name writes:
> >> After upgrading from 9.3.6 to 9.4.1 (both installed from packages on
> >> yum.postgresql.org) we have started getting segfaults of different backends.
> >> Backtraces of all coredumps look similar:
> >> (gdb) bt
> >> #0 0x000000000066bf9b in BackendIdGetTransactionIds (backendID=<value
> >> optimized out>, xid=0x7f2a1b714798, xmin=0x7f2a1b71479c) at sinvaladt.c:426
> >> #1 0x00000000006287f4 in pgstat_read_current_status () at pgstat.c:2871
> >> #2 0x0000000000628879 in pgstat_fetch_stat_numbackends () at pgstat.c:2342
> >
> > Hmm ... looks to me like BackendIdGetTransactionIds is simply busted.
> > It supposes that there are no inactive entries in the sinval array
> > within the range 0 .. lastBackend. But there can be, in which case
> > dereferencing stateP->proc crashes. The reason it's hard to reproduce
> > is the relatively narrow window between where pgstat_read_current_status
> > saw the backend as active and where we're inspecting its sinval entry.
>
> I’ve also tried to revert dd1a3bcc where this function appeared but couldn’t do it :( If you would be able to make a build without this commit (if it is easier than fix it in right way), I could install it on several production hosts to test it.

Hopefully a fix will be forthcoming shortly. Reverting it won't work
though, no, as it included a catalog bump.

Thanks,

Stephen