Shut down the SIP session timers more gracefully, in order to prevent a possible crash.

(closes issue #16452)
 Reported by: corruptor
 Patches: 
       20091221__issue16452.diff.txt uploaded by tilghman (license 14)
 Tested by: corruptor


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@236802 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -1668,6 +1668,7 @@ struct sip_st_dlg {
 	int st_cached_max_se;                   /*!< Session-Timers cached Session-Expires */
 	enum st_mode st_cached_mode;            /*!< Session-Timers cached M.O. */
 	enum st_refresher st_cached_ref;        /*!< Session-Timers cached refresher */
+	unsigned char quit_flag:1;              /*!< Stop trying to lock; just quit */
 };
 
 
@@ -5797,6 +5798,11 @@ static void __sip_destroy(struct sip_pvt *p, int lockowner, int lockdialoglist)
 {
 	struct sip_request *req;
 
+	if (p->stimer) {
+		ast_free(p->stimer);
+		p->stimer = NULL;
+	}
+
 	if (sip_debug_test_pvt(p))
 		ast_verbose("Really destroying SIP dialog '%s' Method: %s\n", p->callid, sip_methods[p->method].text);
 
@@ -5872,6 +5878,7 @@ static void __sip_destroy(struct sip_pvt *p, int lockowner, int lockdialoglist)
 
 	/* Destroy Session-Timers if allocated */
 	if (p->stimer) {
+		p->stimer->quit_flag = 1;
 		if (p->stimer->st_active == TRUE && p->stimer->st_schedid > -1) {
 			AST_SCHED_DEL_UNREF(sched, p->stimer->st_schedid,
 					dialog_unref(p, "removing session timer ref"));
@@ -23689,25 +23696,34 @@ static int proc_session_timer(const void *vp)
 	} else {
 		p->stimer->st_expirys++;
 		if (p->stimer->st_expirys >= 2) {
+			if (p->stimer->quit_flag) {
+				goto return_unref;
+			}
 			ast_log(LOG_WARNING, "Session-Timer expired - %s\n", p->callid);
-
+			sip_pvt_lock(p);
 			while (p->owner && ast_channel_trylock(p->owner)) {
 				sip_pvt_unlock(p);
 				usleep(1);
+				if (p->stimer && p->stimer->quit_flag) {
+					goto return_unref;
+				}
 				sip_pvt_lock(p);
 			}
 
 			ast_softhangup_nolock(p->owner, AST_SOFTHANGUP_DEV);
 			ast_channel_unlock(p->owner);
+			sip_pvt_unlock(p);
 		}
 	}
 
 return_unref:
 	if (!res) {
 		/* An error occurred.  Stop session timer processing */
-		p->stimer->st_schedid = -1;
-		stop_session_timer(p);
-		
+		if (p->stimer) {
+			p->stimer->st_schedid = -1;
+			stop_session_timer(p);
+		}
+
 		/* If we are not asking to be rescheduled, then we need to release our
 		 * reference to the dialog. */
 		dialog_unref(p, "removing session timer ref");