Re: BUG #12918: Segfault in BackendIdGetTransactionIds

* Vladimir Borodin (root@simply.name) wrote:
>=20
> > 30 =D0=BC=D0=B0=D1=80=D1=82=D0=B0 2015 =D0=B3., =D0=B2 19:33, Tom Lane =
<tgl@sss.pgh.pa.us> =D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0=D0=BB(=D0=B0):
> >=20
> > root@simply.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 bac=
kends.
> >> Backtraces of all coredumps look similar:
> >> (gdb) bt
> >> #0  0x000000000066bf9b in BackendIdGetTransactionIds (backendID=3D<val=
ue
> >> optimized out>, xid=3D0x7f2a1b714798, xmin=3D0x7f2a1b71479c) at sinval=
adt.c:426
> >> #1  0x00000000006287f4 in pgstat_read_current_status () at pgstat.c:28=
71
> >> #2  0x0000000000628879 in pgstat_fetch_stat_numbackends () at pgstat.c=
:2342
> >=20
> > 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.
>=20
> I=E2=80=99ve also tried to revert dd1a3bcc where this function appeared b=
ut couldn=E2=80=99t do it :( If you would be able to make a build without t=
his commit (if it is easier than fix it in right way), I could install it o=
n 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