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From b69687377d6afd973a8bc27d8d34bf8069943a9d Mon Sep 17 00:00:00 2001
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From: Mark Reynolds <mreynolds@redhat.com>
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Date: Tue, 19 May 2020 11:25:13 -0400
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Subject: [PATCH] Issue 50745: ns-slapd hangs during CleanAllRUV tests
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Bug Description:
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The hang condition:
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- is not systematic
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- occurs in rare case, for example here during the deletion of a replica.
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- a thread is waiting for a dblock that an other thread "forgot" to
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release.
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- have always existed, at least since 1.4.0 but likely since 1.2.x
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When deleting a replica, the replica is retrieved from
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mapping tree structure (mtnode).
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The replica is also retrieved through the mapping tree
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when writing updates to the changelog.
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When deleting the replica, mapping tree structure is cleared
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after the changelog is deleted (that can take some cycles).
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There is a window where an update can retrieve the replica,
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from the not yet cleared MT, while the changelog being removed.
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At the end, the update will update the changelog that is
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currently removed and keeps an unfree lock in the DB.
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Fix description:
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Ideally mapping tree should be protected by a lock but it
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is not done systematically (e.g. slapi_get_mapping_tree_node).
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Using a lock looks an overkill and can probably introduce
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deadlock and performance hit.
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The idea of the fix is to reduce the window, moving the
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mapping tree clear before the changelog removal.
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https://pagure.io/389-ds-base/issue/50745
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Reviewed by: Mark Reynolds, Ludwig Krispenz
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---
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ldap/servers/plugins/replication/repl5_replica_config.c | 6 +++---
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1 file changed, 3 insertions(+), 3 deletions(-)
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diff --git a/ldap/servers/plugins/replication/repl5_replica_config.c b/ldap/servers/plugins/replication/repl5_replica_config.c
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index 80a079784..95b7fa50e 100644
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--- a/ldap/servers/plugins/replication/repl5_replica_config.c
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+++ b/ldap/servers/plugins/replication/repl5_replica_config.c
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@@ -735,18 +735,18 @@ replica_config_delete(Slapi_PBlock *pb __attribute__((unused)),
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PR_ASSERT(mtnode_ext);
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if (mtnode_ext->replica) {
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+ Object *repl_obj = mtnode_ext->replica;
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/* remove object from the hash */
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r = (Replica *)object_get_data(mtnode_ext->replica);
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+ mtnode_ext->replica = NULL;
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PR_ASSERT(r);
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/* The changelog for this replica is no longer valid, so we should remove it. */
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slapi_log_err(SLAPI_LOG_WARNING, repl_plugin_name, "replica_config_delete - "
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"The changelog for replica %s is no longer valid since "
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"the replica config is being deleted. Removing the changelog.\n",
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slapi_sdn_get_dn(replica_get_root(r)));
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- cl5DeleteDBSync(mtnode_ext->replica);
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+ cl5DeleteDBSync(repl_obj);
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replica_delete_by_name(replica_get_name(r));
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- object_release(mtnode_ext->replica);
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- mtnode_ext->replica = NULL;
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}
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PR_Unlock(s_configLock);
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--
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2.26.2
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