Re: BUG #12918: Segfault in BackendIdGetTransactionIds

> 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.

>
> regards, tom lane

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