Index: channels/chan_iax2.c
===================================================================
diff -u -N -r55c8daf88b94f74e334ab246c51bdb7b469eedc4 -rcf98c744d5bb7e5f015f201bc79c58462f7aaaed
--- a/channels/chan_iax2.c	(.../chan_iax2.c)	(revision 55c8daf88b94f74e334ab246c51bdb7b469eedc4)
+++ b/channels/chan_iax2.c	(.../chan_iax2.c)	(revision cf98c744d5bb7e5f015f201bc79c58462f7aaaed)
@@ -395,8 +395,6 @@
 static struct io_context *io;
 static struct ast_sched_context *sched;
 
-#define DONT_RESCHEDULE -2
-
 static iax2_format iax2_capability = IAX_CAPABILITY_FULLBANDWIDTH;
 
 static int iaxdebug = 0;
@@ -864,6 +862,8 @@
 	int frames_dropped;
 	/*! received frame count: (just for stats) */
 	int frames_received;
+	/*! Destroying this call initiated. */
+	int destroy_initiated;
 	/*! num bytes used for calltoken ie, even an empty ie should contain 2 */
 	unsigned char calltoken_ie_len;
 	/*! hold all signaling frames from the pbx thread until we have a destination callno */
@@ -1672,37 +1672,55 @@
 	return ast_sched_add(con, when, callback, data);
 }
 
+/*
+ * \brief Acquire the iaxsl[callno] if call exists and not having ongoing hangup.
+ * \param callno Call number to lock.
+ * \return 0 If call disappeared or has ongoing hangup procedure. 1 If call found and mutex is locked.
+ */
+static int iax2_lock_callno_unless_destroyed(int callno)
+{
+	ast_mutex_lock(&iaxsl[callno]);
+
+	/* We acquired the lock; but the call was already destroyed (we came after full hang up procedures)
+	 * or destroy initiated (in middle of hang up procedure. */
+	if (!iaxs[callno] || iaxs[callno]->destroy_initiated) {
+		ast_debug(3, "I wanted to lock callno %d, but it is dead or going to die.\n", callno);
+		ast_mutex_unlock(&iaxsl[callno]);
+		return 0;
+	}
+
+	/* Lock acquired, and callno is alive and kicking. */
+	return 1;
+}
+
 static int send_ping(const void *data);
 
 static void __send_ping(const void *data)
 {
-	int callno = (long) data;
+	int callno = PTR_TO_CALLNO(data);
 
-	ast_mutex_lock(&iaxsl[callno]);
+	if (iax2_lock_callno_unless_destroyed(callno) == 0) {
+		ast_debug(3, "Hangup initiated on call %d, aborting __send_ping\n", callno);
+		return;
+	}
 
-	if (iaxs[callno]) {
-		if (iaxs[callno]->peercallno) {
-			send_command(iaxs[callno], AST_FRAME_IAX, IAX_COMMAND_PING, 0, NULL, 0, -1);
-			if (iaxs[callno]->pingid != DONT_RESCHEDULE) {
-				iaxs[callno]->pingid = iax2_sched_add(sched, ping_time * 1000, send_ping, data);
-			}
-		}
-	} else {
-		ast_debug(1, "I was supposed to send a PING with callno %d, but no such call exists.\n", callno);
+	/* Mark pingid as invalid scheduler id. */
+	iaxs[callno]->pingid = -1;
+
+	/* callno is now locked. */
+	if (iaxs[callno]->peercallno) {
+		/* Send PING packet. */
+		send_command(iaxs[callno], AST_FRAME_IAX, IAX_COMMAND_PING, 0, NULL, 0, -1);
+
+		/* Schedule sending next ping. */
+		iaxs[callno]->pingid = iax2_sched_add(sched, ping_time * 1000, send_ping, data);
 	}
 
 	ast_mutex_unlock(&iaxsl[callno]);
 }
 
 static int send_ping(const void *data)
 {
-	int callno = (long) data;
-	ast_mutex_lock(&iaxsl[callno]);
-	if (iaxs[callno] && iaxs[callno]->pingid != DONT_RESCHEDULE) {
-		iaxs[callno]->pingid = -1;
-	}
-	ast_mutex_unlock(&iaxsl[callno]);
-
 #ifdef SCHED_MULTITHREADED
 	if (schedule_action(__send_ping, data))
 #endif
@@ -1743,33 +1761,30 @@
 
 static void __send_lagrq(const void *data)
 {
-	int callno = (long) data;
+	int callno = PTR_TO_CALLNO(data);
 
-	ast_mutex_lock(&iaxsl[callno]);
+	if (iax2_lock_callno_unless_destroyed(callno) == 0) {
+		ast_debug(3, "Hangup initiated on call %d, aborting __send_lagrq\n", callno);
+		return;
+	}
 
-	if (iaxs[callno]) {
-		if (iaxs[callno]->peercallno) {
-			send_command(iaxs[callno], AST_FRAME_IAX, IAX_COMMAND_LAGRQ, 0, NULL, 0, -1);
-			if (iaxs[callno]->lagid != DONT_RESCHEDULE) {
-				iaxs[callno]->lagid = iax2_sched_add(sched, lagrq_time * 1000, send_lagrq, data);
-			}
-		}
-	} else {
-		ast_debug(1, "I was supposed to send a LAGRQ with callno %d, but no such call exists.\n", callno);
+	/* Mark lagid as invalid scheduler id. */
+	iaxs[callno]->lagid = -1;
+
+	/* callno is now locked. */
+	if (iaxs[callno]->peercallno) {
+		/* Send LAGRQ packet. */
+		send_command(iaxs[callno], AST_FRAME_IAX, IAX_COMMAND_LAGRQ, 0, NULL, 0, -1);
+
+		/* Schedule sending next lagrq. */
+		iaxs[callno]->lagid = iax2_sched_add(sched, lagrq_time * 1000, send_lagrq, data);
 	}
 
 	ast_mutex_unlock(&iaxsl[callno]);
 }
 
 static int send_lagrq(const void *data)
 {
-	int callno = (long) data;
-	ast_mutex_lock(&iaxsl[callno]);
-	if (iaxs[callno] && iaxs[callno]->lagid != DONT_RESCHEDULE) {
-		iaxs[callno]->lagid = -1;
-	}
-	ast_mutex_unlock(&iaxsl[callno]);
-
 #ifdef SCHED_MULTITHREADED
 	if (schedule_action(__send_lagrq, data))
 #endif
@@ -2053,6 +2068,16 @@
 	return res;
 }
 
+/* Call AST_SCHED_DEL on a scheduled task if it is found in scheduler. */
+static int iax2_delete_from_sched(const void* data)
+{
+	int sched_id = (int)(long)data;
+
+	AST_SCHED_DEL(sched, sched_id);
+
+	return 0;
+}
+
 /*!\note Assumes the lock on the pvt is already held, when
  * iax2_destroy_helper() is called. */
 static void iax2_destroy_helper(struct chan_iax2_pvt *pvt)
@@ -2069,11 +2094,27 @@
 
 		ast_clear_flag64(pvt, IAX_MAXAUTHREQ);
 	}
-	/* No more pings or lagrq's */
-	AST_SCHED_DEL_SPINLOCK(sched, pvt->pingid, &iaxsl[pvt->callno]);
-	pvt->pingid = DONT_RESCHEDULE;
-	AST_SCHED_DEL_SPINLOCK(sched, pvt->lagid, &iaxsl[pvt->callno]);
-	pvt->lagid = DONT_RESCHEDULE;
+
+
+	/* Mark call destroy initiated flag. */
+	pvt->destroy_initiated = 1;
+
+	/*
+	 * Schedule deleting the scheduled (but didn't run yet) PINGs or LAGRQs.
+	 * Already running tasks will be terminated because of destroy_initiated.
+	 *
+	 * Don't call AST_SCHED_DEL from this thread for pingid and lagid because
+	 * it leads to a deadlock between the scheduler thread callback locking
+	 * the callno mutex and this thread which holds the callno mutex one or
+	 * more times.  It is better to have another thread delete the scheduled
+	 * callbacks which doesn't lock the callno mutex.
+	 */
+	iax2_sched_add(sched, 0, iax2_delete_from_sched, (void*)(long)pvt->pingid);
+	iax2_sched_add(sched, 0, iax2_delete_from_sched, (void*)(long)pvt->lagid);
+
+	pvt->pingid = -1;
+	pvt->lagid = -1;
+
 	AST_SCHED_DEL(sched, pvt->autoid);
 	AST_SCHED_DEL(sched, pvt->authid);
 	AST_SCHED_DEL(sched, pvt->initid);
Index: main/sched.c
===================================================================
diff -u -N -reb9448a1ae18bf16074346bdaae5e0d29d3bcd38 -rcf98c744d5bb7e5f015f201bc79c58462f7aaaed
--- a/main/sched.c	(.../sched.c)	(revision eb9448a1ae18bf16074346bdaae5e0d29d3bcd38)
+++ b/main/sched.c	(.../sched.c)	(revision cf98c744d5bb7e5f015f201bc79c58462f7aaaed)
@@ -513,16 +513,8 @@
 
 	if (!s && *last_id != id) {
 		ast_debug(1, "Attempted to delete nonexistent schedule entry %d!\n", id);
-#ifndef AST_DEVMODE
-		ast_assert(s != NULL);
-#else
-		{
-			char buf[100];
-
-			snprintf(buf, sizeof(buf), "s != NULL, id=%d", id);
-			_ast_assert(0, buf, file, line, function);
-		}
-#endif
+		/* Removing nonexistent schedule entry shouldn't trigger assert (it was enabled in DEV_MODE);
+		 * because in many places entries is deleted without having valid id. */
 		*last_id = id;
 		return -1;
 	} else if (!s) {