Ticket #47409 - allow setting db deadlock rejection policy

https://fedorahosted.org/389/ticket/47409
Reviewed by: nhosoi (Thanks!)
Branch: master
Fix Description: Add the db config attribute nsslapd-db-deadlock-policy.  This
takes values from 1-9.  The values correspond to the deadlock detector modes
in db.h.  These are the valid values to pass to the DBENV->lock_detect
method for the atype parameter.  The default value is 9 (DB_LOCK_YOUNGEST) -
select the youngest locker and reject it.  A value of 0 (DB_LOCK_NORUN) means
to disable deadlock detection and rejection - not recommended except for
testing purposes.  Attempting to use other values will cause an error.
Platforms tested: RHEL6 x86_64
Flag Day: no
Doc impact: yes - document new config parameter

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

@@ -4466,6 +4466,7 @@ static int deadlock_threadmain(void *param)
     dblayer_private *priv = NULL;
     struct ldbminfo *li = NULL;
     PRIntervalTime    interval;   /*NSPR timeout stuffy*/
+    u_int32_t flags = 0;
 
     PR_ASSERT(NULL != param);
     li = (struct ldbminfo*)param;
@@ -4480,13 +4481,19 @@ static int deadlock_threadmain(void *param)
     {
         if (priv->dblayer_enable_transactions) 
         {
-            if (dblayer_db_uses_locking(priv->dblayer_env->dblayer_DB_ENV)) {
-                int aborted;
-                if ((rval = LOCK_DETECT(priv->dblayer_env->dblayer_DB_ENV,
-                                        0, DB_LOCK_YOUNGEST, &aborted)) != 0) {
+            DB_ENV *db_env = priv->dblayer_env->dblayer_DB_ENV;
+            u_int32_t deadlock_policy = priv->dblayer_deadlock_policy;
+
+            if (dblayer_db_uses_locking(db_env) && (deadlock_policy > DB_LOCK_NORUN)) {
+                int rejected = 0;
+
+                if ((rval = LOCK_DETECT(db_env, 0, deadlock_policy, &rejected)) != 0) {
                     LDAPDebug(LDAP_DEBUG_ANY,
-                      "Serious Error---Failed in deadlock detect (aborted at 0x%x), err=%d (%s)\n",
-                      aborted, rval, dblayer_strerror(rval));
+                              "Serious Error---Failed in deadlock detect (aborted at 0x%x), err=%d (%s)\n",
+                              rejected, rval, dblayer_strerror(rval));
+                } else if (rejected) {
+                    LDAPDebug1Arg(LDAP_DEBUG_TRACE, "deadlock_threadmain: found and rejected %d lock requests\n", rejected);
+
                 }
             }
         }

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

@@ -178,6 +178,7 @@ struct dblayer_private
     PRCondVar *thread_count_cv;     /* condition variable for housekeeping thread shutdown */
     int dblayer_lockdown;           /* use DB_LOCKDOWN */
     int dblayer_lock_config;
+    u_int32_t dblayer_deadlock_policy;    /* i.e. the atype to DB_ENV->lock_detect in deadlock_threadmain */
 };
 
 #if 1000*DB_VERSION_MAJOR + 100*DB_VERSION_MINOR >= 4300

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

@@ -1394,6 +1394,40 @@ static int ldbm_config_db_tx_max_set(
     return retval;
 }
 
+static void *ldbm_config_db_deadlock_policy_get(void *arg)
+{
+    struct ldbminfo *li = (struct ldbminfo *) arg;
+
+    return (void *) ((uintptr_t)li->li_dblayer_private->dblayer_deadlock_policy);
+}
+
+static int ldbm_config_db_deadlock_policy_set(void *arg, void *value, char *errorbuf, int phase, int apply)
+{
+    struct ldbminfo *li = (struct ldbminfo *) arg;
+    int retval = LDAP_SUCCESS;
+    u_int32_t val = (u_int32_t) ((uintptr_t)value);
+
+    if ((val < DB_LOCK_NORUN) || (val > DB_LOCK_YOUNGEST)) {
+	    PR_snprintf(errorbuf, SLAPI_DSE_RETURNTEXT_SIZE,
+	                "Error: Invalid value for %s (%d). Must be between %d and %d inclusive",
+	                CONFIG_DB_DEADLOCK_POLICY, val, DB_LOCK_DEFAULT, DB_LOCK_YOUNGEST);
+	    LDAPDebug1Arg(LDAP_DEBUG_ANY, "%s\n", errorbuf);
+	    return LDAP_UNWILLING_TO_PERFORM;
+    }
+    if (val == DB_LOCK_NORUN) {
+	    PR_snprintf(errorbuf, SLAPI_DSE_RETURNTEXT_SIZE,
+	                "Warning: Setting value for %s to (%d) will disable deadlock detection",
+	                CONFIG_DB_DEADLOCK_POLICY, val);
+	    LDAPDebug1Arg(LDAP_DEBUG_ANY, "%s\n", errorbuf);
+    }
+
+    if (apply) {
+        li->li_dblayer_private->dblayer_deadlock_policy = val;
+    }
+
+    return retval;
+}
+
 
 /*------------------------------------------------------------------------
  * Configuration array for ldbm and dblayer variables
@@ -1458,6 +1492,7 @@ static config_info ldbm_config[] = {
     {CONFIG_PAGEDIDLISTSCANLIMIT, CONFIG_TYPE_INT, "0", &ldbm_config_pagedallidsthreshold_get, &ldbm_config_pagedallidsthreshold_set, CONFIG_FLAG_ALWAYS_SHOW|CONFIG_FLAG_ALLOW_RUNNING_CHANGE},
     {CONFIG_RANGELOOKTHROUGHLIMIT, CONFIG_TYPE_INT, "5000", &ldbm_config_rangelookthroughlimit_get, &ldbm_config_rangelookthroughlimit_set, CONFIG_FLAG_ALWAYS_SHOW|CONFIG_FLAG_ALLOW_RUNNING_CHANGE},
     {CONFIG_BACKEND_OPT_LEVEL, CONFIG_TYPE_INT, "1", &ldbm_config_backend_opt_level_get, &ldbm_config_backend_opt_level_set, CONFIG_FLAG_ALWAYS_SHOW},
+    {CONFIG_DB_DEADLOCK_POLICY, CONFIG_TYPE_INT, STRINGIFYDEFINE(DB_LOCK_YOUNGEST), &ldbm_config_db_deadlock_policy_get, &ldbm_config_db_deadlock_policy_set, CONFIG_FLAG_ALWAYS_SHOW|CONFIG_FLAG_ALLOW_RUNNING_CHANGE},
     {NULL, 0, NULL, NULL, NULL, 0}
 };
 

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

@@ -164,6 +164,8 @@ struct config_info {
 
 #define CONFIG_USE_LEGACY_ERRORCODE     "nsslapd-do-not-use-vlv-error"
 
+#define CONFIG_DB_DEADLOCK_POLICY	"nsslapd-db-deadlock-policy"
+
 #define CONFIG_LDBM_DN "cn=config,cn=ldbm database,cn=plugins,cn=config"
 
 #define LDBM_INSTANCE_CONFIG_DONT_WRITE 1

ldap/servers/slapd/slapi-plugin.h

@@ -107,6 +107,9 @@ NSPR_API(PRUint32) PR_fprintf(struct PRFileDesc* fd, const char *fmt, ...)
 #define BERLEN_T "u"
 #endif
 
+#define DEFINETOSTR(xxx) #xxx
+#define STRINGIFYDEFINE(xxx) DEFINETOSTR(xxx)
+
 /* Common check on berval before accessing the contents. */
 /* bv is a struct berval *bv */
 #define BV_HAS_DATA(bv) ((bv != NULL) && (bv->bv_len > 0) && (bv->bv_val != NULL))