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From 70e6c68196d381d05d35414c138894b54939d236 Mon Sep 17 00:00:00 2001
From: Thierry Bordaz <tbordaz@redhat.com>
Date: Thu, 7 Jun 2018 16:19:34 +0200
Subject: [PATCH] Ticket 49765 - Async operations can hang when the server is
 running nunc-stans

Bug Description:
	The fix https://pagure.io/389-ds-base/issue/48184 allowed to schedule
	several NS handlers where each handler waits for the dispatch of the
	previous handler before being schedule.

	In case the current handler is never called (connection inactivity)
	those that are waiting can wait indefinitely (until timeout or connection
	closure). But those that are waiting delay the processing of the operation
	when the scheduling is called by connection_threadmain.

	The some operations can appear hanging.
	This scenario happens with async operations

Fix Description:
	Instead of waiting for the completion of the scheduled handler,
	evaluates if the scheduled handler needs to be cleared (ns_job_done)
	or the waiting  handler to be canceled.

https://pagure.io/389-ds-base/issue/49765

Reviewed by: Mark Reynolds (thanks Mark !)

Platforms tested: F26

Flag Day: no

Doc impact: no
---
 ldap/servers/slapd/daemon.c         | 142 +++++++++++++++-------------
 src/nunc-stans/include/nunc-stans.h |   3 +
 src/nunc-stans/ns/ns_thrpool.c      |   5 +
 3 files changed, 84 insertions(+), 66 deletions(-)

diff --git a/ldap/servers/slapd/daemon.c b/ldap/servers/slapd/daemon.c
index 35cfe7de0..0a723c4a8 100644
--- a/ldap/servers/slapd/daemon.c
+++ b/ldap/servers/slapd/daemon.c
@@ -152,12 +152,21 @@ accept_and_configure(int s __attribute__((unused)), PRFileDesc *pr_acceptfd, PRN
  */
 static int handle_new_connection(Connection_Table *ct, int tcps, PRFileDesc *pr_acceptfd, int secure, int local, Connection **newconn);
 static void ns_handle_new_connection(struct ns_job_t *job);
+static void ns_handle_closure(struct ns_job_t *job);
 static void handle_pr_read_ready(Connection_Table *ct, PRIntn num_poll);
 static int clear_signal(struct POLL_STRUCT *fds);
 static void unfurl_banners(Connection_Table *ct, daemon_ports_t *ports, PRFileDesc **n_tcps, PRFileDesc **s_tcps, PRFileDesc **i_unix);
 static int write_pid_file(void);
 static int init_shutdown_detect(void);
 
+#define NS_HANDLER_NEW_CONNECTION   0
+#define NS_HANDLER_READ_CONNECTION  1
+#define NS_HANDLER_CLOSE_CONNECTION 2
+static ns_job_func_t ns_handlers[] = {
+    ns_handle_new_connection,
+    ns_handle_pr_read_ready,
+    ns_handle_closure
+};
 /*
  * NSPR has different implementations for PRMonitor, depending
  * on the availble threading model
@@ -1058,7 +1067,7 @@ slapd_daemon(daemon_ports_t *ports, ns_thrpool_t *tp)
         for (size_t ii = 0; ii < listeners; ++ii) {
             listener_idxs[ii].ct = the_connection_table; /* to pass to handle_new_connection */
             ns_result_t result = ns_add_io_job(tp, listener_idxs[ii].listenfd, NS_JOB_ACCEPT | NS_JOB_PERSIST | NS_JOB_PRESERVE_FD,
-                                               ns_handle_new_connection, &listener_idxs[ii], &(listener_idxs[ii].ns_job));
+                                               ns_handlers[NS_HANDLER_NEW_CONNECTION], &listener_idxs[ii], &(listener_idxs[ii].ns_job));
             if (result != NS_SUCCESS) {
                 slapi_log_err(SLAPI_LOG_CRIT, "slapd_daemon", "ns_add_io_job failed to create add acceptor %d\n", result);
             }
@@ -1684,28 +1693,84 @@ ns_handle_closure(struct ns_job_t *job)
 /**
  * Schedule more I/O for this connection, or make sure that it
  * is closed in the event loop.
+ * 
  * caller must hold c_mutex
- * It returns
- *  0 on success
- *  1 on need to retry
  */
-static int
-ns_connection_post_io_or_closing_try(Connection *conn)
+void
+ns_connection_post_io_or_closing(Connection *conn)
 {
     struct timeval tv;
 
     if (!enable_nunc_stans) {
-        return 0;
+        return;
     }
 
     /*
      * A job was already scheduled.
-     * Let it be dispatched first
+     * Check if it is the appropriate one
      */
     if (conn->c_job != NULL) {
-        return 1;
+        if (connection_is_free(conn, 0)) {
+            PRStatus shutdown_status;
+
+            /* The connection being freed,
+             * It means that ns_handle_closure already completed and the connection
+             * is no longer on the active list.
+             * The scheduled job is useless and scheduling a new one as well
+             */
+            shutdown_status = ns_job_done(conn->c_job);
+            if (shutdown_status != PR_SUCCESS) {
+                slapi_log_err(SLAPI_LOG_CRIT, "ns_connection_post_io_or_closing", "Failed cancel a job on a freed connection %d !\n", conn->c_sd);
+            }
+            conn->c_job = NULL;
+            return;
+        }
+        if (CONN_NEEDS_CLOSING(conn)) {
+            if (ns_job_is_func(conn->c_job, ns_handlers[NS_HANDLER_CLOSE_CONNECTION])) {
+                /* Due to the closing state we would schedule a ns_handle_closure
+                 * but one is already registered.
+                 * Just return;
+                 */
+                slapi_log_err(SLAPI_LOG_CONNS, "ns_connection_post_io_or_closing", "Already ns_handle_closure "
+                        "job in progress on conn %" PRIu64 " for fd=%d\n",
+                        conn->c_connid, conn->c_sd);
+                return;
+            } else {
+                /* Due to the closing state we would schedule a ns_handle_closure
+                 * but a different handler is registered. Stop it and schedule (below) ns_handle_closure
+                 */
+                ns_job_done(conn->c_job);
+                conn->c_job = NULL;
+            }
+        } else {
+            /* Here the connection is still active => ignore the call and return */
+            if (ns_job_is_func(conn->c_job, ns_handlers[NS_HANDLER_READ_CONNECTION])) {
+                /* Connection is still active and a read_ready is already scheduled
+                 * Likely a consequence of async operations
+                 * Just let the current read_ready do its job
+                 */
+                slapi_log_err(SLAPI_LOG_CONNS, "ns_connection_post_io_or_closing", "Already ns_handle_pr_read_ready "
+                                                                               "job in progress on conn %" PRIu64 " for fd=%d\n",
+                          conn->c_connid, conn->c_sd);
+            } else {
+                /* Weird situation where the connection is not flagged closing but ns_handle_closure
+                 * is scheduled.
+                 * We should not try to read it anymore
+                 */
+                PR_ASSERT(ns_job_is_func(conn->c_job, ns_handlers[NS_HANDLER_CLOSE_CONNECTION]));
+            }
+            return;
+        }
     }
 
+    /* At this point conn->c_job is NULL
+     * Either it was null when the function was called
+     * Or we cleared it (+ns_job_done) if the wrong (according
+     * to the connection state) handler was scheduled
+     *
+     * Now we need to determine which handler to schedule
+     */
+
     if (CONN_NEEDS_CLOSING(conn)) {
         /* there should only ever be 0 or 1 active closure jobs */
         PR_ASSERT((conn->c_ns_close_jobs == 0) || (conn->c_ns_close_jobs == 1));
@@ -1718,7 +1783,7 @@ ns_connection_post_io_or_closing_try(Connection *conn)
             conn->c_ns_close_jobs++;                                                      /* now 1 active closure job */
             connection_acquire_nolock_ext(conn, 1 /* allow acquire even when closing */); /* event framework now has a reference */
             /* Close the job asynchronously. Why? */
-            ns_result_t job_result = ns_add_job(conn->c_tp, NS_JOB_TIMER, ns_handle_closure, conn, &(conn->c_job));
+            ns_result_t job_result = ns_add_job(conn->c_tp, NS_JOB_TIMER, ns_handlers[NS_HANDLER_CLOSE_CONNECTION], conn, &(conn->c_job));
             if (job_result != NS_SUCCESS) {
                 if (job_result == NS_SHUTDOWN) {
                     slapi_log_err(SLAPI_LOG_INFO, "ns_connection_post_io_or_closing", "post closure job "
@@ -1762,7 +1827,7 @@ ns_connection_post_io_or_closing_try(Connection *conn)
 #endif
         ns_result_t job_result = ns_add_io_timeout_job(conn->c_tp, conn->c_prfd, &tv,
                                                        NS_JOB_READ | NS_JOB_PRESERVE_FD,
-                                                       ns_handle_pr_read_ready, conn, &(conn->c_job));
+                                                       ns_handlers[NS_HANDLER_READ_CONNECTION], conn, &(conn->c_job));
         if (job_result != NS_SUCCESS) {
             if (job_result == NS_SHUTDOWN) {
                 slapi_log_err(SLAPI_LOG_INFO, "ns_connection_post_io_or_closing", "post I/O job for "
@@ -1782,61 +1847,6 @@ ns_connection_post_io_or_closing_try(Connection *conn)
     return 0;
 }
 
-/*
- * Tries to schedule I/O for this connection
- * If the connection is already busy with a scheduled I/O
- * it can wait until scheduled I/O is dispatched
- *
- * caller must hold c_mutex
- */
-void
-ns_connection_post_io_or_closing(Connection *conn)
-{
-    while (ns_connection_post_io_or_closing_try(conn)) {
-        /* Here a job is currently scheduled (c->job is set) and not yet dispatched
-         * Job can be either:
-         *  - ns_handle_closure
-         *  - ns_handle_pr_read_ready
-         */
-
-        if (connection_is_free(conn, 0)) {
-            PRStatus shutdown_status;
-
-            /* The connection being freed,
-             * It means that ns_handle_closure already completed and the connection
-             * is no longer on the active list.
-             * The scheduled job is useless and scheduling a new one as well
-             */
-            shutdown_status = ns_job_done(conn->c_job);
-            if (shutdown_status != PR_SUCCESS) {
-                slapi_log_err(SLAPI_LOG_CRIT, "ns_connection_post_io_or_closing", "Failed cancel a job on a freed connection %d !\n", conn->c_sd);
-            }
-            conn->c_job = NULL;
-            return;
-        }
-        if (g_get_shutdown() && CONN_NEEDS_CLOSING(conn)) {
-            PRStatus shutdown_status;
-
-            /* This is shutting down cancel any scheduled job to register ns_handle_closure
-             */
-            shutdown_status = ns_job_done(conn->c_job);
-            if (shutdown_status != PR_SUCCESS) {
-                slapi_log_err(SLAPI_LOG_CRIT, "ns_connection_post_io_or_closing", "Failed to cancel a job during shutdown %d !\n", conn->c_sd);
-            }
-            conn->c_job = NULL;
-            continue;
-        }
-
-        /* We are not suppose to work immediately on the connection that is taken by
-         * another job
-         * release the lock and give some time
-         */
-        PR_ExitMonitor(conn->c_mutex);
-        DS_Sleep(PR_MillisecondsToInterval(100));
-        PR_EnterMonitor(conn->c_mutex);
-    }
-}
-
 /* This function must be called without the thread flag, in the
  * event loop.  This function may free the connection.  This can
  * only be done in the event loop thread.
diff --git a/src/nunc-stans/include/nunc-stans.h b/src/nunc-stans/include/nunc-stans.h
index 192e38ec3..a0ddbdb42 100644
--- a/src/nunc-stans/include/nunc-stans.h
+++ b/src/nunc-stans/include/nunc-stans.h
@@ -959,4 +959,7 @@ ns_result_t ns_thrpool_wait(struct ns_thrpool_t *tp);
  */
 ns_result_t ns_job_rearm(struct ns_job_t *job);
 
+int
+ns_job_is_func(struct ns_job_t *job, ns_job_func_t func);
+
 #endif /* NS_THRPOOL_H */
diff --git a/src/nunc-stans/ns/ns_thrpool.c b/src/nunc-stans/ns/ns_thrpool.c
index d95b0c38b..774607c88 100644
--- a/src/nunc-stans/ns/ns_thrpool.c
+++ b/src/nunc-stans/ns/ns_thrpool.c
@@ -1237,6 +1237,11 @@ ns_job_rearm(ns_job_t *job)
     /* Unreachable code .... */
     return NS_INVALID_REQUEST;
 }
+int
+ns_job_is_func(struct ns_job_t *job, ns_job_func_t func)
+{
+    return(job && job->func == func);
+}
 
 static void
 ns_thrpool_delete(ns_thrpool_t *tp)
-- 
2.17.1