[lttng-dev] [PATCH lttng-tools 1/2] Fix: relayd: don't call lttng_ht_destroy in RCU read-side C.S.

[Jérémie Galarneau]

Merged in master and stable-2.7.

Thanks!
Jérémie

On Thu, Sep 17, 2015 at 12:48 PM, Mathieu Desnoyers
<mathieu.desnoyers at efficios.com> wrote:
> It is forbidden to call lttng_ht_destroy() within a RCU read-side
> critical section.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> ---
>  src/bin/lttng-relayd/session.c | 15 ++++++++-------
>  src/bin/lttng-relayd/stream.c  |  5 +++++
>  2 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/src/bin/lttng-relayd/session.c b/src/bin/lttng-relayd/session.c
> index 14ae874..2300e5f 100644
> --- a/src/bin/lttng-relayd/session.c
> +++ b/src/bin/lttng-relayd/session.c
> @@ -131,7 +131,14 @@ static void rcu_destroy_session(struct rcu_head *rcu_head)
>         struct relay_session *session =
>                         caa_container_of(rcu_head, struct relay_session,
>                                 rcu_node);
> -
> +       /*
> +        * Since each trace has a reference on the session, it means
> +        * that if we are at the point where we teardown the session, no
> +        * trace belonging to that session exist at this point.
> +        * Calling lttng_ht_destroy in call_rcu worker thread so we
> +        * don't hold the RCU read-side lock while calling it.
> +        */
> +       lttng_ht_destroy(session->ctf_traces_ht);
>         free(session);
>  }
>
> @@ -155,12 +162,6 @@ static void destroy_session(struct relay_session *session)
>
>         ret = session_delete(session);
>         assert(!ret);
> -       /*
> -        * Since each trace has a reference on the session, it means
> -        * that if we are at the point where we teardown the session, no
> -        * trace belonging to that session exist at this point.
> -        */
> -       lttng_ht_destroy(session->ctf_traces_ht);
>         call_rcu(&session->rcu_node, rcu_destroy_session);
>  }
>
> diff --git a/src/bin/lttng-relayd/stream.c b/src/bin/lttng-relayd/stream.c
> index b604919..8825d09 100644
> --- a/src/bin/lttng-relayd/stream.c
> +++ b/src/bin/lttng-relayd/stream.c
> @@ -253,6 +253,11 @@ static void stream_unpublish(struct relay_stream *stream)
>  static void stream_destroy(struct relay_stream *stream)
>  {
>         if (stream->indexes_ht) {
> +               /*
> +                * Calling lttng_ht_destroy in call_rcu worker thread so
> +                * we don't hold the RCU read-side lock while calling
> +                * it.
> +                */
>                 lttng_ht_destroy(stream->indexes_ht);
>         }
>         if (stream->tfa) {
> --
> 2.1.4
>



-- 
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com