Deadlock between dahdi_request() and pri_dchannel() processing an incomming call.

The sig_pri_new_ast_channel() is called with the channel private lock held
when pri_dchannel() calls it and no channel private lock held when
dahdi_request() calls it.  The use of pri_grab() in
sig_pri_new_ast_channel() could leave the channel private lock held when
it returns if the lock was not held before calling it.

Make sig_pri_new_ast_channel() just lock the PRI span lock instead of
using pri_grab().  It is safe to do this because dahdi_request() does not
have the channel private lock and the deadlock potential with the PRI span
lock is only between pri_dchannel() and other threads.


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@301946 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/sig_pri.c

@@ -880,11 +880,10 @@ static struct ast_channel *sig_pri_new_ast_channel(struct sig_pri_chan *p, int s
 	if (transfercapability & AST_TRANS_CAP_DIGITAL) {
 		sig_pri_set_digital(p, 1);
 	}
-	if (p->pri && !pri_grab(p, p->pri)) {
+	if (p->pri) {
+		ast_mutex_lock(&p->pri->lock);
 		sig_pri_span_devstate_changed(p->pri);
-		pri_rel(p->pri);
-	} else {
-		ast_log(LOG_WARNING, "Failed to grab PRI!\n");
+		ast_mutex_unlock(&p->pri->lock);
 	}
 
 	return c;