In PGSharedMemoryIsInUse, assume that EACCES indicates a shmem segment

that is of no concern to us --- it must belong to a different userid,
which means it is not a Postgres shmem segment (or at least,
not one that is relevant to our data directory).  I plan a more extensive
fix in HEAD, but this is a simple change that prevents failure-to-reboot
problems for single-postmaster installations.

diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 9ec046071c9777c94e0d4fa497fde1433d747d33..b44f07c8ec5288026971c9f32ebfbfa61283b584 100644 (file)
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/port/sysv_shmem.c,v 1.24.2.1 2003/11/07 21:56:01 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/port/sysv_shmem.c,v 1.24.2.2 2004/11/09 20:35:16 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -191,10 +191,6 @@ PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
        /*
         * We detect whether a shared memory segment is in use by seeing
         * whether it (a) exists and (b) has any processes are attached to it.
-        *
-        * If we are unable to perform the stat operation for a reason other than
-        * nonexistence of the segment (most likely, because it doesn't belong
-        * to our userid), assume it is in use.
         */
        if (shmctl(shmId, IPC_STAT, &shmStat) < 0)
        {
@@ -205,7 +201,18 @@ PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
                 */
                if (errno == EINVAL)
                        return false;
-               /* Else assume segment is in use */
+               /*
+                * EACCES implies that the segment belongs to some other userid,
+                * which means it is not a Postgres shmem segment (or at least,
+                * not one that is relevant to our data directory).
+                */
+               if (errno == EACCES)
+                       return false;
+               /*
+                * Otherwise, we had better assume that the segment is in use.
+                * The only likely case is EIDRM, which implies that the segment
+                * has been IPC_RMID'd but there are still processes attached to it.
+                */
                return true;
        }
        /* If it has attached processes, it's in use */