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

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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
This commit is contained in:
Frederic LE FOLL
2017-06-08 19:28:12 +02:00
parent 85dff8e26e
commit dc307af7f2
1 changed files with 7 additions and 0 deletions
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7
main/pbx_app.c
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@@ -396,6 +396,11 @@ int ast_unregister_application(const char *app)
struct ast_app *cur; struct ast_app *cur;
int cmp; 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_WRLOCK(&apps);
AST_RWLIST_TRAVERSE_SAFE_BEGIN(&apps, cur, list) { AST_RWLIST_TRAVERSE_SAFE_BEGIN(&apps, cur, list) {
cmp = strcasecmp(app, cur->name); cmp = strcasecmp(app, cur->name);
@@ -418,6 +423,8 @@ int ast_unregister_application(const char *app)
AST_RWLIST_TRAVERSE_SAFE_END; AST_RWLIST_TRAVERSE_SAFE_END;
AST_RWLIST_UNLOCK(&apps); AST_RWLIST_UNLOCK(&apps);
ast_unlock_contexts();
return cur ? 0 : -1; return cur ? 0 : -1;
} }