From d1981719adbcc05fa15f540e8fc4327907991fc6 Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Fri, 31 Jan 2014 21:31:08 -0500 Subject: [PATCH] Clear MyProc and MyProcSignalState before they become invalid. Evidence from buildfarm member crake suggests that the new test_shm_mq module is routinely crashing the server due to the arrival of a SIGUSR1 after the shared memory segment has been unmapped. Although processes using the new dynamic background worker facilities are more likely to receive a SIGUSR1 around this time, the problem is also possible on older branches, so I'm back-patching the parts of this change that apply to older branches as far as they apply. It's already generally the case that code checks whether these pointers are NULL before deferencing them, so the important thing is mostly to make sure that they do get set to NULL before they become invalid. But in master, there's one case in procsignal_sigusr1_handler that lacks a NULL guard, so add that. Patch by me; review by Tom Lane. --- src/backend/storage/ipc/procsignal.c | 9 +++++- src/backend/storage/lmgr/proc.c | 42 +++++++++++++++++----------- 2 files changed, 33 insertions(+), 18 deletions(-) diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c index 6ebabce72f..6526b2688a 100644 --- a/src/backend/storage/ipc/procsignal.c +++ b/src/backend/storage/ipc/procsignal.c @@ -149,6 +149,13 @@ CleanupProcSignalState(int status, Datum arg) slot = &ProcSignalSlots[pss_idx - 1]; Assert(slot == MyProcSignalSlot); + /* + * Clear MyProcSignalSlot, so that a SIGUSR1 received after this point + * won't try to access it after it's no longer ours (and perhaps even + * after we've unmapped the shared memory segment). + */ + MyProcSignalSlot = NULL; + /* sanity check */ if (slot->pss_pid != MyProcPid) { @@ -285,7 +292,7 @@ procsignal_sigusr1_handler(SIGNAL_ARGS) if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN)) RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN); - if (set_latch_on_sigusr1) + if (set_latch_on_sigusr1 && MyProc != NULL) SetLatch(&MyProc->procLatch); latch_sigusr1_handler(); diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1a683b8336..9d32f9405d 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -773,6 +773,7 @@ ProcKill(int code, Datum arg) { /* use volatile pointer to prevent code rearrangement */ volatile PROC_HDR *procglobal = ProcGlobal; + PGPROC *proc; Assert(MyProc != NULL); @@ -797,31 +798,34 @@ ProcKill(int code, Datum arg) */ LWLockReleaseAll(); - /* Release ownership of the process's latch, too */ - DisownLatch(&MyProc->procLatch); + /* + * Clear MyProc first; then disown the process latch. This is so that + * signal handlers won't try to clear the process latch after it's no + * longer ours. + */ + proc = MyProc; + MyProc = NULL; + DisownLatch(&proc->procLatch); SpinLockAcquire(ProcStructLock); /* Return PGPROC structure (and semaphore) to appropriate freelist */ if (IsAnyAutoVacuumProcess()) { - MyProc->links.next = (SHM_QUEUE *) procglobal->autovacFreeProcs; - procglobal->autovacFreeProcs = MyProc; + proc->links.next = (SHM_QUEUE *) procglobal->autovacFreeProcs; + procglobal->autovacFreeProcs = proc; } else if (IsBackgroundWorker) { - MyProc->links.next = (SHM_QUEUE *) procglobal->bgworkerFreeProcs; - procglobal->bgworkerFreeProcs = MyProc; + proc->links.next = (SHM_QUEUE *) procglobal->bgworkerFreeProcs; + procglobal->bgworkerFreeProcs = proc; } else { - MyProc->links.next = (SHM_QUEUE *) procglobal->freeProcs; - procglobal->freeProcs = MyProc; + proc->links.next = (SHM_QUEUE *) procglobal->freeProcs; + procglobal->freeProcs = proc; } - /* PGPROC struct isn't mine anymore */ - MyProc = NULL; - /* Update shared estimate of spins_per_delay */ procglobal->spins_per_delay = update_spins_per_delay(procglobal->spins_per_delay); @@ -850,6 +854,7 @@ AuxiliaryProcKill(int code, Datum arg) { int proctype = DatumGetInt32(arg); PGPROC *auxproc PG_USED_FOR_ASSERTS_ONLY; + PGPROC *proc; Assert(proctype >= 0 && proctype < NUM_AUXILIARY_PROCS); @@ -860,16 +865,19 @@ AuxiliaryProcKill(int code, Datum arg) /* Release any LW locks I am holding (see notes above) */ LWLockReleaseAll(); - /* Release ownership of the process's latch, too */ - DisownLatch(&MyProc->procLatch); + /* + * Clear MyProc first; then disown the process latch. This is so that + * signal handlers won't try to clear the process latch after it's no + * longer ours. + */ + proc = MyProc; + MyProc = NULL; + DisownLatch(&proc->procLatch); SpinLockAcquire(ProcStructLock); /* Mark auxiliary proc no longer in use */ - MyProc->pid = 0; - - /* PGPROC struct isn't mine anymore */ - MyProc = NULL; + proc->pid = 0; /* Update shared estimate of spins_per_delay */ ProcGlobal->spins_per_delay = update_spins_per_delay(ProcGlobal->spins_per_delay);