Unlock the sip channel during fax detection like chan_dahdi does to prevent a deadloc...

(closes issue ASTERISK-17798)
tested by mnicholson

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.6.2@323039 65c4cc65-6c06-0410-ace0-fbb531ad65f3

diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index b7f2ef2d8a8ca2a2a66b98a587ae1ae3858e6131..7908a14b0a87212a215a98527d0ec63ddbe2bd5f 100644 (file)
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -7369,11 +7369,18 @@ static struct ast_frame *sip_read(struct ast_channel *ast)
 
        /* If we detect a CNG tone and fax detection is enabled then send us off to the fax extension */
        if (faxdetected && ast_test_flag(&p->flags[1], SIP_PAGE2_FAX_DETECT_CNG)) {
-               ast_channel_lock(ast);
                if (strcmp(ast->exten, "fax")) {
                        const char *target_context = S_OR(ast->macrocontext, ast->context);
+                       /* We need to unlock 'ast' here because
+                        * ast_exists_extension has the potential to start and
+                        * stop an autoservice on the channel. Such action is
+                        * prone to deadlock if the channel is locked.
+                        */
+                       sip_pvt_unlock(p);
                        ast_channel_unlock(ast);
                        if (ast_exists_extension(ast, target_context, "fax", 1, ast->cid.cid_num)) {
+                               ast_channel_lock(ast);
+                               sip_pvt_lock(p);
                                ast_verbose(VERBOSE_PREFIX_2 "Redirecting '%s' to fax extension due to CNG detection\n", ast->name);
                                pbx_builtin_setvar_helper(ast, "FAXEXTEN", ast->exten);
                                if (ast_async_goto(ast, target_context, "fax", 1)) {
@@ -7381,10 +7388,10 @@ static struct ast_frame *sip_read(struct ast_channel *ast)
                                }
                                fr = &ast_null_frame;
                        } else {
+                               ast_channel_lock(ast);
+                               sip_pvt_lock(p);
                                ast_log(LOG_NOTICE, "FAX CNG detected but no fax extension\n");
                         }
-               } else {
-                       ast_channel_unlock(ast);
                 }
         }