From 0ad95bc8a048e165148c68c5bdec5555b25218a9 Mon Sep 17 00:00:00 2001
From: Frederic LE FOLL <frederic.lefoll@c-s.fr>
Date: Thu, 8 Jun 2017 19:28:12 +0200
Subject: [PATCH] Core/PBX: Deadlock between dialplan execution and application
unregistration.
Not easy to reproduce, but we have noticed deadlocks when unloading a module
while dialplan is handling a request.
The deadlock is between :
1) Dialplan execution: pbx_extension_helper() first taking conlock,
then pbx_findapp() [when called] asking for lock on apps list.
2) Application unregistration: ast_unregister_application() first taking lock
on apps list, then unreference_cached_app() [when called] asking for conlock.
As a protection, I suggest to modify ast_unregister_application(), so that it
anticipates the need of conlock, before taking the lock on apps list.
The side effect is a longer unavailability of conlock when unregistering an
application.
ASTERISK-27041
Change-Id: I0db0f1eb320da6a5758cce3a47d765be1face8e2
---
main/pbx_app.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/main/pbx_app.c b/main/pbx_app.c
index e0609db70e..ec6bc75890 100644
--- a/main/pbx_app.c
+++ b/main/pbx_app.c
@@ -394,6 +394,11 @@ int ast_unregister_application(const char *app)
struct ast_app *cur;
int cmp;
+ /* Anticipate need for conlock in unreference_cached_app(), in order to avoid
+ * possible deadlock with pbx_extension_helper()/pbx_findapp()
+ */
+ ast_rdlock_contexts();
+
AST_RWLIST_WRLOCK(&apps);
AST_RWLIST_TRAVERSE_SAFE_BEGIN(&apps, cur, list) {
cmp = strcasecmp(app, cur->name);
@@ -416,6 +421,8 @@ int ast_unregister_application(const char *app)
AST_RWLIST_TRAVERSE_SAFE_END;
AST_RWLIST_UNLOCK(&apps);
+ ast_unlock_contexts();
+
return cur ? 0 : -1;
}
--
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