Fix POTS flash hook to orignate a second call deadlock.

A deadlock can occur when a POTS phone tries to flash hook to originate a
second call for 3-way or transfer.  If another process is scanning the
channels container when the POTS line flash hooks then a deadlock will
occur.

* Release the channel and private locks when creating a new channel as a
result of a flash hook.

(closes issue ASTERISK-19842)
Reported by: rmudgett
Tested by: rmudgett
........

Merged revisions 368644 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 368645 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@368646 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_dahdi.c

@@ -8603,8 +8603,18 @@ static struct ast_frame *dahdi_handle_event(struct ast_channel *ast)
 						ast_log(LOG_WARNING, "Unable to allocate three-way subchannel\n");
 						goto winkflashdone;
 					}
-					/* Make new channel */
+
+					/*
+					 * Make new channel
+					 *
+					 * We cannot hold the p or ast locks while creating a new
+					 * channel.
+					 */
+					ast_mutex_unlock(&p->lock);
+					ast_channel_unlock(ast);
 					chan = dahdi_new(p, AST_STATE_RESERVED, 0, SUB_THREEWAY, 0, NULL);
+					ast_channel_lock(ast);
+					ast_mutex_lock(&p->lock);
 					if (p->dahditrcallerid) {
 						if (!p->origcid_num)
 							p->origcid_num = ast_strdup(p->cid_num);

channels/sig_analog.c

@@ -3205,8 +3205,18 @@ static struct ast_frame *__analog_handle_event(struct analog_pvt *p, struct ast_
 						ast_log(LOG_WARNING, "Unable to allocate three-way subchannel\n");
 						goto winkflashdone;
 					}
-					/* Make new channel */
+
+					/*
+					 * Make new channel
+					 *
+					 * We cannot hold the p or ast locks while creating a new
+					 * channel.
+					 */
+					analog_unlock_private(p);
+					ast_channel_unlock(ast);
 					chan = analog_new_ast_channel(p, AST_STATE_RESERVED, 0, ANALOG_SUB_THREEWAY, NULL);
+					ast_channel_lock(ast);
+					analog_lock_private(p);
 					if (!chan) {
 						ast_log(LOG_WARNING,
 							"Cannot allocate new call structure on channel %d\n",