From 701dcc983eb4d08dd36bb3a0ddba255819797760 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 30 Mar 2015 13:05:27 -0400 Subject: [PATCH] Fix rare core dump in BackendIdGetTransactionIds(). BackendIdGetTransactionIds() neglected the possibility that the PROC pointer in a ProcState array entry is null. In current usage, this could only crash if the other backend had exited since pgstat_read_current_status saw it as active, which is a pretty narrow window. But it's reachable in the field, per bug #12918 from Vladimir Borodin. Back-patch to 9.4 where the faulty code was introduced. --- src/backend/storage/ipc/sinvaladt.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/src/backend/storage/ipc/sinvaladt.c b/src/backend/storage/ipc/sinvaladt.c index 81b85c0e42..a2fde89b52 100644 --- a/src/backend/storage/ipc/sinvaladt.c +++ b/src/backend/storage/ipc/sinvaladt.c @@ -403,9 +403,7 @@ BackendIdGetProc(int backendID) void BackendIdGetTransactionIds(int backendID, TransactionId *xid, TransactionId *xmin) { - ProcState *stateP; SISeg *segP = shmInvalBuffer; - PGXACT *xact; *xid = InvalidTransactionId; *xmin = InvalidTransactionId; @@ -415,11 +413,16 @@ BackendIdGetTransactionIds(int backendID, TransactionId *xid, TransactionId *xmi if (backendID > 0 && backendID <= segP->lastBackend) { - stateP = &segP->procState[backendID - 1]; - xact = &ProcGlobal->allPgXact[stateP->proc->pgprocno]; + ProcState *stateP = &segP->procState[backendID - 1]; + PGPROC *proc = stateP->proc; - *xid = xact->xid; - *xmin = xact->xmin; + if (proc != NULL) + { + PGXACT *xact = &ProcGlobal->allPgXact[proc->pgprocno]; + + *xid = xact->xid; + *xmin = xact->xmin; + } } LWLockRelease(SInvalWriteLock); -- 2.39.5