Back-patch assorted latch-related fixes.

Fix a whole bunch of signal handlers that had been hacked to do things that
might change errno, without adding the necessary save/restore logic for
errno.  Also make some minor fixes in unix_latch.c, and clean up bizarre
and unsafe scheme for disowning the process's latch.  While at it, rename
the PGPROC latch field to procLatch for consistency with 9.2.

Issues noted while reviewing a patch by Peter Geoghegan.

1 files changed, 31 insertions, 11 deletions

diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index 9ef008e7331..58d95bc0d6b 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -187,7 +187,8 @@ InitProcGlobal(void)
 	ProcGlobal->spins_per_delay = DEFAULT_SPINS_PER_DELAY;
 
 	/*
-	 * Pre-create the PGPROC structures and create a semaphore for each.
+	 * Pre-create the PGPROC structures and create a semaphore and latch
+	 * for each.
 	 */
 	procs = (PGPROC *) ShmemAlloc((MaxConnections) * sizeof(PGPROC));
 	if (!procs)
@@ -198,9 +199,9 @@ InitProcGlobal(void)
 	for (i = 0; i < MaxConnections; i++)
 	{
 		PGSemaphoreCreate(&(procs[i].sem));
+		InitSharedLatch(&procs[i].procLatch);
 		procs[i].links.next = (SHM_QUEUE *) ProcGlobal->freeProcs;
 		ProcGlobal->freeProcs = &procs[i];
-		InitSharedLatch(&procs[i].waitLatch);
 	}
 
 	/*
@@ -217,9 +218,9 @@ InitProcGlobal(void)
 	for (i = 0; i < autovacuum_max_workers + 1; i++)
 	{
 		PGSemaphoreCreate(&(procs[i].sem));
+		InitSharedLatch(&procs[i].procLatch);
 		procs[i].links.next = (SHM_QUEUE *) ProcGlobal->autovacFreeProcs;
 		ProcGlobal->autovacFreeProcs = &procs[i];
-		InitSharedLatch(&procs[i].waitLatch);
 	}
 
 	/*
@@ -230,7 +231,7 @@ InitProcGlobal(void)
 	{
 		AuxiliaryProcs[i].pid = 0;		/* marks auxiliary proc as not in use */
 		PGSemaphoreCreate(&(AuxiliaryProcs[i].sem));
-		InitSharedLatch(&procs[i].waitLatch);
+		InitSharedLatch(&AuxiliaryProcs[i].procLatch);
 	}
 
 	/* Create ProcStructLock spinlock, too */
@@ -306,8 +307,8 @@ InitProcess(void)
 		MarkPostmasterChildActive();
 
 	/*
-	 * Initialize all fields of MyProc, except for the semaphore which was
-	 * prepared for us by InitProcGlobal.
+	 * Initialize all fields of MyProc, except for the semaphore and latch,
+	 * which were prepared for us by InitProcGlobal.
 	 */
 	SHMQueueElemInit(&(MyProc->links));
 	MyProc->waitStatus = STATUS_OK;
@@ -333,12 +334,17 @@ InitProcess(void)
 		SHMQueueInit(&(MyProc->myProcLocks[i]));
 	MyProc->recoveryConflictPending = false;
 
-	/* Initialise for sync rep */
+	/* Initialize fields for sync rep */
 	MyProc->waitLSN.xlogid = 0;
 	MyProc->waitLSN.xrecoff = 0;
 	MyProc->syncRepState = SYNC_REP_NOT_WAITING;
 	SHMQueueElemInit(&(MyProc->syncRepLinks));
-	OwnLatch(&MyProc->waitLatch);
+
+	/*
+	 * Acquire ownership of the PGPROC's latch, so that we can use WaitLatch.
+	 * Note that there's no particular need to do ResetLatch here.
+	 */
+	OwnLatch(&MyProc->procLatch);
 
 	/*
 	 * We might be reusing a semaphore that belonged to a failed process. So
@@ -379,7 +385,6 @@ InitProcessPhase2(void)
 	/*
 	 * Arrange to clean that up at backend exit.
 	 */
-	on_shmem_exit(SyncRepCleanupAtProcExit, 0);
 	on_shmem_exit(RemoveProcFromArray, 0);
 }
 
@@ -454,8 +459,8 @@ InitAuxiliaryProcess(void)
 	SpinLockRelease(ProcStructLock);
 
 	/*
-	 * Initialize all fields of MyProc, except for the semaphore which was
-	 * prepared for us by InitProcGlobal.
+	 * Initialize all fields of MyProc, except for the semaphore and latch,
+	 * which were prepared for us by InitProcGlobal.
 	 */
 	SHMQueueElemInit(&(MyProc->links));
 	MyProc->waitStatus = STATUS_OK;
@@ -476,6 +481,12 @@ InitAuxiliaryProcess(void)
 		SHMQueueInit(&(MyProc->myProcLocks[i]));
 
 	/*
+	 * Acquire ownership of the PGPROC's latch, so that we can use WaitLatch.
+	 * Note that there's no particular need to do ResetLatch here.
+	 */
+	OwnLatch(&MyProc->procLatch);
+
+	/*
 	 * We might be reusing a semaphore that belonged to a failed process. So
 	 * be careful and reinitialize its value here.	(This is not strictly
 	 * necessary anymore, but seems like a good idea for cleanliness.)
@@ -677,6 +688,9 @@ ProcKill(int code, Datum arg)
 
 	Assert(MyProc != NULL);
 
+	/* Make sure we're out of the sync rep lists */
+	SyncRepCleanupAtProcExit();
+
 	/*
 	 * Release any LW locks I am holding.  There really shouldn't be any, but
 	 * it's cheap to check again before we cut the knees off the LWLock
@@ -684,6 +698,9 @@ ProcKill(int code, Datum arg)
 	 */
 	LWLockReleaseAll();
 
+	/* Release ownership of the process's latch, too */
+	DisownLatch(&MyProc->procLatch);
+
 	SpinLockAcquire(ProcStructLock);
 
 	/* Return PGPROC structure (and semaphore) to appropriate freelist */
@@ -739,6 +756,9 @@ 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);
+
 	SpinLockAcquire(ProcStructLock);
 
 	/* Mark auxiliary proc no longer in use */