Fix deadlock when executing CLI "pri show channels" and "ss7 show channels" commands.

* Fix sig_pri_lock_owner() to avoid deadlock properly.

* Code pri_grab() better.

* Fix sig_ss7_lock_owner() to avoid deadlock properly.

* Code ss7_grab() better.

(closes issue ASTERISK-19854)
Reported by: Jaxon
Patches:
      jira_asterisk_19854_v1.8.6.patch (license #5621) patch uploaded by rmudgett (Modified to do the same thing to sig_ss7)
Tested by: Jaxon
........

Merged revisions 367976 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 367978 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@367979 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 15 insertions, 21 deletions

diff --git a/channels/sig_pri.c b/channels/sig_pri.c
index e94f08ef5..4be5269fc 100644
--- a/channels/sig_pri.c
+++ b/channels/sig_pri.c
@@ -115,13 +115,6 @@ static int pri_gendigittimeout = 8000;
 
 #define DCHAN_AVAILABLE	(DCHAN_NOTINALARM | DCHAN_UP)
 
-#define PRI_DEADLOCK_AVOIDANCE(p) \
-	do { \
-		sig_pri_unlock_private(p); \
-		usleep(1); \
-		sig_pri_lock_private(p); \
-	} while (0)
-
 static int pri_active_dchan_index(struct sig_pri_span *pri);
 
 static const char *sig_pri_call_level2str(enum sig_pri_call_level level)
@@ -349,23 +342,23 @@ static void sig_pri_deadlock_avoidance_private(struct sig_pri_chan *p)
 		p->calls->deadlock_avoidance_private(p->chan_pvt);
 	} else {
 		/* Fallback to the old way if callback not present. */
-		PRI_DEADLOCK_AVOIDANCE(p);
+		sig_pri_unlock_private(p);
+		sched_yield();
+		sig_pri_lock_private(p);
 	}
 }
 
 static void pri_grab(struct sig_pri_chan *p, struct sig_pri_span *pri)
 {
-	int res;
-
 	/* Grab the lock first */
-	do {
-		res = ast_mutex_trylock(&pri->lock);
-		if (res) {
-			sig_pri_deadlock_avoidance_private(p);
-		}
-	} while (res);
+	while (ast_mutex_trylock(&pri->lock)) {
+		/* Avoid deadlock */
+		sig_pri_deadlock_avoidance_private(p);
+	}
 	/* Then break the poll */
-	pthread_kill(pri->master, SIGURG);
+	if (pri->master != AST_PTHREADT_NULL) {
+		pthread_kill(pri->master, SIGURG);
+	}
 }
 
 /*!
@@ -1205,10 +1198,11 @@ static void sig_pri_lock_owner(struct sig_pri_span *pri, int chanpos)
 			/* We got the lock */
 			break;
 		}
-		/* We must unlock the PRI to avoid the possibility of a deadlock */
-		ast_mutex_unlock(&pri->lock);
-		sig_pri_deadlock_avoidance_private(pri->pvts[chanpos]);
-		ast_mutex_lock(&pri->lock);
+
+		/* Avoid deadlock */
+		sig_pri_unlock_private(pri->pvts[chanpos]);
+		DEADLOCK_AVOIDANCE(&pri->lock);
+		sig_pri_lock_private(pri->pvts[chanpos]);
 	}
 }