Bug 745259 - Incorrect entryUSN index under high load

             in replicated environment

https://bugzilla.redhat.com/show_bug.cgi?id=745259

Description:
. Changed the backend entry lock from PRLock to PRMonitor to
  allow re-entrant locking.  In ldbm_back_delete and ldbm_
  back_modify, backend entry lock was released before calling
  be_preop plugins and re-acquired just after that to avoid
  the deadlock by the be_preop plugins called from the same
  thread. The short no-lock window was the cause of the entry-
  usn corruption.  By replacing PRLock with the re-entrant
  PRMonitor, we could eliminate the no-lock window.
. Cleaned up compiler warnings.

ldap/servers/slapd/back-ldbm/back-ldbm.h

@@ -350,19 +350,19 @@ struct backcommon {
 
 /* From ep_type through ep_size MUST be identical to backcommon */
 struct backentry {
-    int               ep_type;       /* to distinguish backdn from backentry */
-    struct backcommon *ep_lrunext;   /* for the cache */
-    struct backcommon *ep_lruprev;   /* for the cache */
-    ID                ep_id;         /* entry id */
-    char              ep_state;      /* state in the cache */
-    int               ep_refcnt;     /* entry reference cnt */
+    int               ep_type;      /* to distinguish backdn from backentry */
+    struct backcommon *ep_lrunext;  /* for the cache */
+    struct backcommon *ep_lruprev;  /* for the cache */
+    ID                ep_id;        /* entry id */
+    char              ep_state;     /* state in the cache */
+    int               ep_refcnt;    /* entry reference cnt */
     size_t            ep_size;      /* for cache tracking */
-    Slapi_Entry       *ep_entry;     /* real entry */
+    Slapi_Entry       *ep_entry;    /* real entry */
     Slapi_Entry       *ep_vlventry;
-    void *            ep_dn_link;    /* linkage for the 3 hash */
-    void *            ep_id_link;    /*     tables used for */
-    void *            ep_uuid_link;  /*     looking up entries */
-    PRLock            *ep_mutexp;    /* protection for mods */
+    void *            ep_dn_link;   /* linkage for the 3 hash */
+    void *            ep_id_link;   /*     tables used for */
+    void *            ep_uuid_link; /*     looking up entries */
+    PRMonitor         *ep_mutexp;   /* protection for mods; make it reentrant */
 };
 
 /* From ep_type through ep_size MUST be identical to backcommon */

ldap/servers/slapd/back-ldbm/backentry.c

@@ -56,7 +56,7 @@ backentry_free( struct backentry **bep )
 		slapi_entry_free( ep->ep_entry );
 	}
 	if ( ep->ep_mutexp != NULL ) {
-		PR_DestroyLock( ep->ep_mutexp );
+		PR_DestroyMonitor( ep->ep_mutexp );
 	}
 	slapi_ch_free( (void**)&ep );
 	*bep = NULL;

ldap/servers/slapd/back-ldbm/cache.c

@@ -1437,19 +1437,28 @@ int cache_lock_entry(struct cache *cache, struct backentry *e)
     if (! e->ep_mutexp) {
        /* make sure only one thread does this */
        PR_Lock(cache->c_emutexalloc_mutex);
-       if (! e->ep_mutexp)
-           e->ep_mutexp = PR_NewLock();
+       if (! e->ep_mutexp) {
+           e->ep_mutexp = PR_NewMonitor();
+           if (!e->ep_mutexp) {
+               LOG("<= cache_lock_entry (DELETED)\n", 0, 0, 0);
+               LDAPDebug1Arg(LDAP_DEBUG_ANY,
+                     "cache_lock_entry: failed to create a lock for %s\n",
+					 backentry_get_ndn(e));
+               LOG("<= cache_lock_entry (FAILED)\n", 0, 0, 0);
+               return 1;
+           }
+       }
        PR_Unlock(cache->c_emutexalloc_mutex);
     }
 
     /* wait on entry lock (done w/o holding the cache lock) */
-    PR_Lock(e->ep_mutexp);
+    PR_EnterMonitor(e->ep_mutexp);
 
     /* make sure entry hasn't been deleted now */
     PR_Lock(cache->c_mutex);
     if (e->ep_state & (ENTRY_STATE_DELETED|ENTRY_STATE_NOTINCACHE)) {
        PR_Unlock(cache->c_mutex);
-       PR_Unlock(e->ep_mutexp);
+       PR_ExitMonitor(e->ep_mutexp);
        LOG("<= cache_lock_entry (DELETED)\n", 0, 0, 0);
        return 1;
     }
@@ -1463,7 +1472,7 @@ int cache_lock_entry(struct cache *cache, struct backentry *e)
 void cache_unlock_entry(struct cache *cache, struct backentry *e)
 {
     LOG("=> cache_unlock_entry\n", 0, 0, 0);
-    PR_Unlock(e->ep_mutexp);
+    PR_ExitMonitor(e->ep_mutexp);
 }
 
 /* DN cache */

ldap/servers/slapd/back-ldbm/id2entry.c

@@ -95,7 +95,6 @@ id2entry_add_ext( backend *be, struct backentry *e, back_txn *txn, int encrypt
         memset(&data, 0, sizeof(data));
         if (entryrdn_get_switch())
         {
-            Slapi_Attr *eattr = NULL;
             struct backdn *oldbdn = NULL;
             Slapi_DN *sdn =
                          slapi_sdn_dup(slapi_entry_get_sdn_const(entry_to_use));

ldap/servers/slapd/back-ldbm/ldbm_delete.c

@@ -210,11 +210,9 @@ ldbm_back_delete( Slapi_PBlock *pb )
 			goto error_return;
 		}
 		slapi_pblock_set(pb, SLAPI_RESULT_CODE, &ldap_result_code);
-		/* have to unlock the entry here, in case the bepreop attempts
-		   to modify the same entry == deadlock */
-		cache_unlock_entry( &inst->inst_cache, e );
+
 		rc = plugin_call_plugins(pb, SLAPI_PLUGIN_BE_PRE_DELETE_FN);
-		cache_lock_entry( &inst->inst_cache, e );
+
 		if (rc == -1)
 		{
 			/* 

ldap/servers/slapd/back-ldbm/ldbm_modify.c

@@ -307,11 +307,9 @@ ldbm_back_modify( Slapi_PBlock *pb )
 	/* ec is the entry that our bepreop should get to mess with */
 	slapi_pblock_set( pb, SLAPI_MODIFY_EXISTING_ENTRY, ec->ep_entry );
 	slapi_pblock_set(pb, SLAPI_RESULT_CODE, &ldap_result_code);
-	/* have to unlock the entry here, in case the bepreop attempts
-	   to modify the same entry == deadlock */
-	cache_unlock_entry( &inst->inst_cache, e );
+
 	plugin_call_plugins(pb, SLAPI_PLUGIN_BE_PRE_MODIFY_FN);
-	cache_lock_entry( &inst->inst_cache, e );
+
 	slapi_pblock_get(pb, SLAPI_RESULT_CODE, &ldap_result_code);
 	/* The Plugin may have messed about with some of the PBlock parameters... ie. mods */
 	slapi_pblock_get( pb, SLAPI_MODIFY_MODS, &mods );

ldap/servers/slapd/modify.c

@@ -75,7 +75,9 @@
 /* Forward declarations */
 static int modify_internal_pb (Slapi_PBlock *pb);
 static void op_shared_modify (Slapi_PBlock *pb, int pw_change, char *old_pw);
+#if 0 /* not used */
 static void remove_mod (Slapi_Mods *smods, const char *type, Slapi_Mods *smod_unhashed);
+#endif
 static int op_shared_allow_pw_change (Slapi_PBlock *pb, LDAPMod *mod, char **old_pw, Slapi_Mods *smods);
 static int hash_rootpw (LDAPMod **mods);
 
@@ -976,6 +978,7 @@ free_and_return:
 	}
 }
 
+#if 0 /* not used */
 static void remove_mod (Slapi_Mods *smods, const char *type, Slapi_Mods *smod_unhashed)
 {
 	LDAPMod *mod;
@@ -991,6 +994,7 @@ static void remove_mod (Slapi_Mods *smods, const char *type, Slapi_Mods *smod_un
 		}
 	}
 }
+#endif
 
 static int op_shared_allow_pw_change (Slapi_PBlock *pb, LDAPMod *mod, char **old_pw, Slapi_Mods *smods)
 {