[lttng-dev] [PATCH LTTNG-UST] Fix: Cleanup local_apps sock_info in lttng_ust_cleanup

[Mathieu Desnoyers]

Merged into stable-2.6, stable-2.5, master, thanks!

Mathieu

----- On Jul 7, 2015, at 2:35 PM, Jeremie Galarneau jeremie.galarneau at efficios.com wrote:

> LTTng-UST will deadlock after a fork while waiting on the
> "constructor_wait" semaphore if local apps, handled the session daemon
> running under the current UID, are disabled or "not_allowed".
> 
> This deadlock can be triggered by setting an infinite registration
> timeout, clearing the HOME environment variable and launching an app
> which calls FORK(3). This will cause setup_local_apps() to fail to
> determine the local_apps sock_path, thus leaving
> local_apps.allowed == 0.
> 
> This, in turn, would cause lttng_ust_cleanup to skip the cleanup
> of the local_apps sock_info after a fork,
> leaving local_apps.constructor_sem_posted == 1. This would cause
> handle_register_done() in the child to skip over the decrementation
> of sem_count and post of the constructor_wait semaphore.
> 
> Signed-off-by: Jérémie Galarneau <jeremie.galarneau at efficios.com>
> ---
> liblttng-ust/lttng-ust-comm.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
> index b290204..9f71839 100644
> --- a/liblttng-ust/lttng-ust-comm.c
> +++ b/liblttng-ust/lttng-ust-comm.c
> @@ -1554,9 +1554,7 @@ static
> void lttng_ust_cleanup(int exiting)
> {
> 	cleanup_sock_info(&global_apps, exiting);
> -	if (local_apps.allowed) {
> -		cleanup_sock_info(&local_apps, exiting);
> -	}
> +	cleanup_sock_info(&local_apps, exiting);
> 	/*
> 	 * The teardown in this function all affect data structures
> 	 * accessed under the UST lock by the listener thread. This
> --
> 2.4.4

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com