Tighten up error recovery for fast-path locking.

The previous code could cause a backend crash after BEGIN; SAVEPOINT a;
LOCK TABLE foo (interrupted by ^C or statement timeout); ROLLBACK TO
SAVEPOINT a; LOCK TABLE foo, and might have leaked strong-lock counts
in other situations.

Report by Zoltán Böszörményi; patch review by Jeff Davis.

Author: robertmhaas

src/backend/access/transam/xact.c

@@ -2259,7 +2259,7 @@ AbortTransaction(void)
 	 * Also clean up any open wait for lock, since the lock manager will choke
 	 * if we try to wait for another lock before doing this.
 	 */
-	LockWaitCancel();
+	LockErrorCleanup();
 
 	/*
 	 * check the current transaction state
@@ -4144,7 +4144,7 @@ AbortSubTransaction(void)
 	AbortBufferIO();
 	UnlockBuffers();
 
-	LockWaitCancel();
+	LockErrorCleanup();
 
 	/*
 	 * check the current transaction state

src/backend/storage/lmgr/README

@@ -560,7 +560,7 @@ examines every member of the wait queue (this was not true in the 7.0
 implementation, BTW).  Therefore, if ProcLockWakeup is always invoked
 after a lock is released or a wait queue is rearranged, there can be no
 failure to wake a wakable process.  One should also note that
-LockWaitCancel (abort a waiter due to outside factors) must run
+LockErrorCleanup (abort a waiter due to outside factors) must run
 ProcLockWakeup, in case the canceled waiter was soft-blocking other
 waiters.
 

src/backend/storage/lmgr/lock.c

@@ -250,7 +250,8 @@ static HTAB *LockMethodProcLockHash;
 static HTAB *LockMethodLocalHash;
 
 
-/* private state for GrantAwaitedLock */
+/* private state for error cleanup */
+static LOCALLOCK *StrongLockInProgress;
 static LOCALLOCK *awaitedLock;
 static ResourceOwner awaitedOwner;
 
@@ -338,6 +339,8 @@ static void RemoveLocalLock(LOCALLOCK *locallock);
 static PROCLOCK *SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc,
 			     const LOCKTAG *locktag, uint32 hashcode, LOCKMODE lockmode);
 static void GrantLockLocal(LOCALLOCK *locallock, ResourceOwner owner);
+static void BeginStrongLockAcquire(LOCALLOCK *locallock, uint32 fasthashcode);
+static void FinishStrongLockAcquire(void);
 static void WaitOnLock(LOCALLOCK *locallock, ResourceOwner owner);
 static void ReleaseLockForOwner(LOCALLOCK *locallock, ResourceOwner owner);
 static bool UnGrantLock(LOCK *lock, LOCKMODE lockmode,
@@ -738,22 +741,11 @@ LockAcquireExtended(const LOCKTAG *locktag,
 		}
 		else if (FastPathStrongMode(lockmode))
 		{
-			/*
-			 * Adding to a memory location is not atomic, so we take a
-			 * spinlock to ensure we don't collide with someone else trying
-			 * to bump the count at the same time.
-			 *
-			 * XXX: It might be worth considering using an atomic fetch-and-add
-			 * instruction here, on architectures where that is supported.
-			 */
-			Assert(locallock->holdsStrongLockCount == FALSE);
-			SpinLockAcquire(&FastPathStrongRelationLocks->mutex);
-			FastPathStrongRelationLocks->count[fasthashcode]++;
-			locallock->holdsStrongLockCount = TRUE;
-			SpinLockRelease(&FastPathStrongRelationLocks->mutex);
+			BeginStrongLockAcquire(locallock, fasthashcode);
 			if (!FastPathTransferRelationLocks(lockMethodTable, locktag,
 											   hashcode))
 			{
+				AbortStrongLockAcquire();
 				if (reportMemoryError)
 					ereport(ERROR,
 							(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -779,6 +771,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
 								hashcode, lockmode);
 	if (!proclock)
 	{
+		AbortStrongLockAcquire();
 		LWLockRelease(partitionLock);
 		if (reportMemoryError)
 			ereport(ERROR,
@@ -820,6 +813,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
 		 */
 		if (dontWait)
 		{
+			AbortStrongLockAcquire();
 			if (proclock->holdMask == 0)
 			{
 				uint32		proclock_hashcode;
@@ -884,6 +878,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
 		 */
 		if (!(proclock->holdMask & LOCKBIT_ON(lockmode)))
 		{
+			AbortStrongLockAcquire();
 			PROCLOCK_PRINT("LockAcquire: INCONSISTENT", proclock);
 			LOCK_PRINT("LockAcquire: INCONSISTENT", lock, lockmode);
 			/* Should we retry ? */
@@ -894,6 +889,12 @@ LockAcquireExtended(const LOCKTAG *locktag,
 		LOCK_PRINT("LockAcquire: granted", lock, lockmode);
 	}
 
+	/*
+	 * Lock state is fully up-to-date now; if we error out after this, no
+	 * special error cleanup is required.
+	 */
+	FinishStrongLockAcquire();
+
 	LWLockRelease(partitionLock);
 
 	/*
@@ -1349,6 +1350,64 @@ GrantLockLocal(LOCALLOCK *locallock, ResourceOwner owner)
 	locallock->numLockOwners++;
 }
 
+/*
+ * BeginStrongLockAcquire - inhibit use of fastpath for a given LOCALLOCK,
+ * and arrange for error cleanup if it fails
+ */
+static void
+BeginStrongLockAcquire(LOCALLOCK *locallock, uint32 fasthashcode)
+{
+	Assert(StrongLockInProgress == NULL);
+	Assert(locallock->holdsStrongLockCount == FALSE);
+
+	/*
+	 * Adding to a memory location is not atomic, so we take a
+	 * spinlock to ensure we don't collide with someone else trying
+	 * to bump the count at the same time.
+	 *
+	 * XXX: It might be worth considering using an atomic fetch-and-add
+	 * instruction here, on architectures where that is supported.
+	 */
+
+	SpinLockAcquire(&FastPathStrongRelationLocks->mutex);
+	FastPathStrongRelationLocks->count[fasthashcode]++;
+	locallock->holdsStrongLockCount = TRUE;
+	StrongLockInProgress = locallock;
+	SpinLockRelease(&FastPathStrongRelationLocks->mutex);
+}
+
+/*
+ * FinishStrongLockAcquire - cancel pending cleanup for a strong lock
+ * acquisition once it's no longer needed
+ */
+static void
+FinishStrongLockAcquire(void)
+{
+	StrongLockInProgress = NULL;
+}
+
+/*
+ * AbortStrongLockAcquire - undo strong lock state changes performed by
+ * BeginStrongLockAcquire.
+ */
+void
+AbortStrongLockAcquire(void)
+{
+	uint32	fasthashcode;
+	LOCALLOCK  *locallock = StrongLockInProgress;
+	
+	if (locallock == NULL)
+		return;
+
+	fasthashcode = FastPathStrongLockHashPartition(locallock->hashcode);
+	Assert(locallock->holdsStrongLockCount == TRUE);
+	SpinLockAcquire(&FastPathStrongRelationLocks->mutex);
+	FastPathStrongRelationLocks->count[fasthashcode]--;
+	locallock->holdsStrongLockCount = FALSE;
+	StrongLockInProgress = NULL;
+	SpinLockRelease(&FastPathStrongRelationLocks->mutex);
+}
+
 /*
  * GrantAwaitedLock -- call GrantLockLocal for the lock we are doing
  *		WaitOnLock on.
@@ -1414,7 +1473,7 @@ WaitOnLock(LOCALLOCK *locallock, ResourceOwner owner)
 	 * We can and do use a PG_TRY block to try to clean up after failure, but
 	 * this still has a major limitation: elog(FATAL) can occur while waiting
 	 * (eg, a "die" interrupt), and then control won't come back here. So all
-	 * cleanup of essential state should happen in LockWaitCancel, not here.
+	 * cleanup of essential state should happen in LockErrorCleanup, not here.
 	 * We can use PG_TRY to clear the "waiting" status flags, since doing that
 	 * is unimportant if the process exits.
 	 */
@@ -1441,7 +1500,7 @@ WaitOnLock(LOCALLOCK *locallock, ResourceOwner owner)
 	}
 	PG_CATCH();
 	{
-		/* In this path, awaitedLock remains set until LockWaitCancel */
+		/* In this path, awaitedLock remains set until LockErrorCleanup */
 
 		/* Report change to non-waiting status */
 		pgstat_report_waiting(false);

src/backend/storage/lmgr/proc.c

@@ -635,17 +635,20 @@ IsWaitingForLock(void)
 }
 
 /*
- * Cancel any pending wait for lock, when aborting a transaction.
+ * Cancel any pending wait for lock, when aborting a transaction, and revert
+ * any strong lock count acquisition for a lock being acquired.
  *
  * (Normally, this would only happen if we accept a cancel/die
- * interrupt while waiting; but an ereport(ERROR) while waiting is
- * within the realm of possibility, too.)
+ * interrupt while waiting; but an ereport(ERROR) before or during the lock
+ * wait is within the realm of possibility, too.)
  */
 void
-LockWaitCancel(void)
+LockErrorCleanup(void)
 {
 	LWLockId	partitionLock;
 
+	AbortStrongLockAcquire();
+
 	/* Nothing to do if we weren't waiting for a lock */
 	if (lockAwaited == NULL)
 		return;
@@ -709,7 +712,7 @@ ProcReleaseLocks(bool isCommit)
 	if (!MyProc)
 		return;
 	/* If waiting, get off wait queue (should only be needed after error) */
-	LockWaitCancel();
+	LockErrorCleanup();
 	/* Release locks */
 	LockReleaseAll(DEFAULT_LOCKMETHOD, !isCommit);
 
@@ -1019,7 +1022,7 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
 	 * NOTE: this may also cause us to exit critical-section state, possibly
 	 * allowing a cancel/die interrupt to be accepted. This is OK because we
 	 * have recorded the fact that we are waiting for a lock, and so
-	 * LockWaitCancel will clean up if cancel/die happens.
+	 * LockErrorCleanup will clean up if cancel/die happens.
 	 */
 	LWLockRelease(partitionLock);
 
@@ -1062,7 +1065,7 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
 	 * don't, because we have no shared-state-change work to do after being
 	 * granted the lock (the grantor did it all).  We do have to worry about
 	 * updating the locallock table, but if we lose control to an error,
-	 * LockWaitCancel will fix that up.
+	 * LockErrorCleanup will fix that up.
 	 */
 	do
 	{
@@ -1207,7 +1210,7 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
 	LWLockAcquire(partitionLock, LW_EXCLUSIVE);
 
 	/*
-	 * We no longer want LockWaitCancel to do anything.
+	 * We no longer want LockErrorCleanup to do anything.
 	 */
 	lockAwaited = NULL;
 

src/backend/tcop/postgres.c

@@ -2575,7 +2575,7 @@ die(SIGNAL_ARGS)
 			/* bump holdoff count to make ProcessInterrupts() a no-op */
 			/* until we are done getting ready for it */
 			InterruptHoldoffCount++;
-			LockWaitCancel();	/* prevent CheckDeadLock from running */
+			LockErrorCleanup();	/* prevent CheckDeadLock from running */
 			DisableNotifyInterrupt();
 			DisableCatchupInterrupt();
 			InterruptHoldoffCount--;
@@ -2617,7 +2617,7 @@ StatementCancelHandler(SIGNAL_ARGS)
 			/* bump holdoff count to make ProcessInterrupts() a no-op */
 			/* until we are done getting ready for it */
 			InterruptHoldoffCount++;
-			LockWaitCancel();	/* prevent CheckDeadLock from running */
+			LockErrorCleanup();	/* prevent CheckDeadLock from running */
 			DisableNotifyInterrupt();
 			DisableCatchupInterrupt();
 			InterruptHoldoffCount--;
@@ -2776,7 +2776,7 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 			/* bump holdoff count to make ProcessInterrupts() a no-op */
 			/* until we are done getting ready for it */
 			InterruptHoldoffCount++;
-			LockWaitCancel();	/* prevent CheckDeadLock from running */
+			LockErrorCleanup();	/* prevent CheckDeadLock from running */
 			DisableNotifyInterrupt();
 			DisableCatchupInterrupt();
 			InterruptHoldoffCount--;

src/include/storage/lock.h

@@ -489,6 +489,7 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag,
 					bool sessionLock,
 					bool dontWait,
 					bool report_memory_error);
+extern void AbortStrongLockAcquire(void);
 extern bool LockRelease(const LOCKTAG *locktag,
 			LOCKMODE lockmode, bool sessionLock);
 extern void LockReleaseSession(LOCKMETHODID lockmethodid);

src/include/storage/proc.h

@@ -244,7 +244,7 @@ extern int	ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable);
 extern PGPROC *ProcWakeup(PGPROC *proc, int waitStatus);
 extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock);
 extern bool IsWaitingForLock(void);
-extern void LockWaitCancel(void);
+extern void LockErrorCleanup(void);
 
 extern void ProcWaitForSignal(void);
 extern void ProcSendSignal(int pid);