[Asterisk-code-review] Core/PBX: Deadlock between dialplan execution and applicatio... (asterisk[master])

[George Joseph]

George Joseph has uploaded this change for review. ( https://gerrit.asterisk.org/5870


Change subject: Core/PBX: Deadlock between dialplan execution and application unregistration.
......................................................................

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
---
M main/pbx_app.c
1 file changed, 7 insertions(+), 0 deletions(-)



  git pull ssh://gerrit.asterisk.org:29418/asterisk refs/changes/70/5870/1

diff --git a/main/pbx_app.c b/main/pbx_app.c
index e0609db..ec6bc75 100644
--- a/main/pbx_app.c
+++ b/main/pbx_app.c
@@ -394,6 +394,11 @@
 	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 @@
 	AST_RWLIST_TRAVERSE_SAFE_END;
 	AST_RWLIST_UNLOCK(&apps);
 
+	ast_unlock_contexts();
+
 	return cur ? 0 : -1;
 }
 

-- 
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Gerrit-Project: asterisk
Gerrit-Branch: master
Gerrit-MessageType: newchange
Gerrit-Change-Id: I0db0f1eb320da6a5758cce3a47d765be1face8e2
Gerrit-Change-Number: 5870
Gerrit-PatchSet: 1
Gerrit-Owner: George Joseph <gjoseph at digium.com>
Gerrit-Reviewer: Frederic LE FOLL <frederic.lefoll at c-s.fr>
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