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From f993a9b5a1ac95728baae201543cad5993a28da1 Mon Sep 17 00:00:00 2001
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From: Ludwig Krispenz <lkrispen@redhat.com>
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Date: Mon, 1 Aug 2016 10:47:31 +0200
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Subject: [PATCH 22/29] Ticket 48882 - server can hang in connection list
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processing
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Bug Description: if a thread holding the connection monitor
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is stuck in polling and the client doesn't
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respond, the main thread can be blocked on
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this connection when iterating the connection
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table.
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Fix Description: Implement a test and enter function for the connection
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monitor, so the main thread will never wait for a
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connection monitor already owned by an other thread
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https://fedorahosted.org/389/ticket/48882
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Reviewed by: Noriko, Thanks
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(cherry picked from commit 7110db91e75f392f1c83643d9aa88895992d9c01)
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---
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ldap/servers/slapd/daemon.c | 69 ++++++++++++++++++++++++++++++++++++++++++++-
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1 file changed, 68 insertions(+), 1 deletion(-)
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diff --git a/ldap/servers/slapd/daemon.c b/ldap/servers/slapd/daemon.c
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index 81a54cf..23c30c3 100644
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--- a/ldap/servers/slapd/daemon.c
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+++ b/ldap/servers/slapd/daemon.c
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@@ -164,6 +164,67 @@ static void unfurl_banners(Connection_Table *ct,daemon_ports_t *ports, PRFileDes
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static int write_pid_file();
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static int init_shutdown_detect();
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+/*
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+ * NSPR has different implementations for PRMonitor, depending
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+ * on the availble threading model
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+ * The PR_TestAndEnterMonitor is not available for pthreads
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+ * so this is a implementation based on the code in
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+ * prmon.c adapted to resemble the implementation in ptsynch.c
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+ *
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+ * The function needs access to the elements of the PRMonitor struct.
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+ * Therfor the pthread variant of PRMonitor is copied here.
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+ */
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+typedef struct MY_PRMonitor {
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+ const char* name;
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+ pthread_mutex_t lock;
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+ pthread_t owner;
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+ pthread_cond_t entryCV;
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+ pthread_cond_t waitCV;
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+ PRInt32 refCount;
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+ PRUint32 entryCount;
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+ PRIntn notifyTimes;
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+} MY_PRMonitor;
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+
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+static PRBool MY_TestAndEnterMonitor(MY_PRMonitor *mon)
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+{
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+ pthread_t self = pthread_self();
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+ PRStatus rv;
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+ PRBool rc = PR_FALSE;
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+
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+ PR_ASSERT(mon != NULL);
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+ rv = pthread_mutex_lock(&mon->lock);
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+ if (rv != 0) {
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+ slapi_log_error(SLAPI_LOG_FATAL ,"TestAndEnterMonitor",
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+ "Failed to acquire monitor mutex, error (%d)\n", rv);
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+ return rc;
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+ }
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+ if (mon->entryCount != 0) {
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+ if (pthread_equal(mon->owner, self))
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+ goto done;
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+ rv = pthread_mutex_unlock(&mon->lock);
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+ if (rv != 0) {
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+ slapi_log_error(SLAPI_LOG_FATAL ,"TestAndEnterMonitor",
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+ "Failed to release monitor mutex, error (%d)\n", rv);
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+ }
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+ return PR_FALSE;
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+ }
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+ /* and now I have the monitor */
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+ PR_ASSERT(mon->notifyTimes == 0);
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+ PR_ASSERT((mon->owner) == 0);
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+ mon->owner = self;
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+
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+done:
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+ mon->entryCount += 1;
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+ rv = pthread_mutex_unlock(&mon->lock);
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+ if (rv == PR_SUCCESS) {
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+ rc = PR_TRUE;
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+ } else {
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+ slapi_log_error(SLAPI_LOG_FATAL ,"TestAndEnterMonitor",
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+ "Failed to release monitor mutex, error (%d)\n", rv);
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+ rc = PR_FALSE;
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+ }
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+ return rc;
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+}
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/* Globals which are used to store the sockets between
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* calls to daemon_pre_setuid_init() and the daemon thread
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* creation. */
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@@ -1552,7 +1613,13 @@ setup_pr_read_pds(Connection_Table *ct, PRFileDesc **n_tcps, PRFileDesc **s_tcps
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}
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else
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{
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- PR_EnterMonitor(c->c_mutex);
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+ /* we try to acquire the connection mutex, if it is already
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+ * acquired by another thread, don't wait
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+ */
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+ if (PR_FALSE == MY_TestAndEnterMonitor((MY_PRMonitor *)c->c_mutex)) {
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+ c = next;
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+ continue;
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+ }
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if (c->c_flags & CONN_FLAG_CLOSING)
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{
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/* A worker thread has marked that this connection
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--
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2.4.11
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