From fddf45b38097d14301d249fbeebca32e40233bd2 Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Wed, 29 Mar 2017 09:44:29 -0400 Subject: [PATCH] Plug race in dsa_attach. With sufficiently bad luck, it was possible for a parallel worker to attempt attach to a DSA area after all other backends have detached from it, which is not legal. If the worker had waited a little longer to get started, the DSM itself would have been destroyed, which is why this wasn't noticed before. Thomas Munro, per a report from Andreas Seltenreich Discussion: http://postgr.es/m/87h92g83t3.fsf@credativ.de --- src/backend/utils/mmgr/dsa.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/src/backend/utils/mmgr/dsa.c b/src/backend/utils/mmgr/dsa.c index 6d5d12a6c9..d08317249b 100644 --- a/src/backend/utils/mmgr/dsa.c +++ b/src/backend/utils/mmgr/dsa.c @@ -1314,6 +1314,13 @@ attach_internal(void *place, dsm_segment *segment, dsa_handle handle) /* Bump the reference count. */ LWLockAcquire(DSA_AREA_LOCK(area), LW_EXCLUSIVE); + if (control->refcnt == 0) + { + /* We can't attach to a DSA area that has already been destroyed. */ + ereport(ERROR, + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), + errmsg("could not attach to dsa_area"))); + } ++control->refcnt; LWLockRelease(DSA_AREA_LOCK(area));