If we're going to have a non-panic check for held_lwlocks[] overrun,

it must occur *before* we get into the critical state of holding a
lock we have no place to record.  Per discussion with Qingqing Zhou.

diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 112690ae903cf87f1d4396ac05a1faf66de78772..f75ccc869ffc4fee4e211318ac3df9f4bb1c6a1e 100644 (file)
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -15,7 +15,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/storage/lmgr/lwlock.c,v 1.26 2005/04/08 03:43:54 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/storage/lmgr/lwlock.c,v 1.27 2005/04/08 14:18:35 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -213,6 +213,10 @@ LWLockAcquire(LWLockId lockid, LWLockMode mode)
     */
    Assert(!(proc == NULL && IsUnderPostmaster));
 
+   /* Ensure we will have room to remember the lock */
+   if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
+       elog(ERROR, "too many LWLocks taken");
+
    /*
     * Lock out cancel/die interrupts until we exit the code section
     * protected by the LWLock.  This ensures that interrupts will not
@@ -328,8 +332,6 @@ LWLockAcquire(LWLockId lockid, LWLockMode mode)
    SpinLockRelease_NoHoldoff(&lock->mutex);
 
    /* Add lock to list of locks held by this backend */
-   if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
-       elog(ERROR, "too many LWLocks taken");
    held_lwlocks[num_held_lwlocks++] = lockid;
 
    /*
@@ -354,6 +356,10 @@ LWLockConditionalAcquire(LWLockId lockid, LWLockMode mode)
 
    PRINT_LWDEBUG("LWLockConditionalAcquire", lockid, lock);
 
+   /* Ensure we will have room to remember the lock */
+   if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
+       elog(ERROR, "too many LWLocks taken");
+
    /*
     * Lock out cancel/die interrupts until we exit the code section
     * protected by the LWLock.  This ensures that interrupts will not
@@ -398,8 +404,6 @@ LWLockConditionalAcquire(LWLockId lockid, LWLockMode mode)
    else
    {
        /* Add lock to list of locks held by this backend */
-       if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
-           elog(ERROR, "too many LWLocks taken");
        held_lwlocks[num_held_lwlocks++] = lockid;
    }