[lttng-dev] [PATCH lttng-tools v2] Fix: race between kconsumerd and sessiond on tear down

[Jérémie Galarneau]

Merged, thanks!

Jérémie

On Thu, Sep 3, 2015 at 5:48 PM, Jonathan Rajotte
<jonathan.rajotte-julien at efficios.com> wrote:
> v2: minimize indentation by using return on condition.
>
> Kconsumerd and sessiond both have reference on lttng-module. This can lead to a race
> on modprobe_remove_lttng_all which might fail to unload modules due to
> certain modules not having a ref count equal to zero at the time.
>
> waitpid is used to force a synchronization on the child (kconsumer) termination.
>
> This also have been applied to ust consumers for the sake of consistency.
>
> Fixes: #878
>
> Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien at efficios.com>
> ---
>  src/bin/lttng-sessiond/main.c | 34 +++++++++++++++++++++++++++++++++-
>  1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
> index d284deb..66a6149 100644
> --- a/src/bin/lttng-sessiond/main.c
> +++ b/src/bin/lttng-sessiond/main.c
> @@ -587,6 +587,34 @@ static int generate_lock_file_path(char *path, size_t len)
>  }
>
>  /*
> + * Wait on consumer process termination.
> + *
> + * Need to be called with the consumer data lock held or from a context
> + * ensuring no concurrent access to data (e.g: cleanup).
> + */
> +static void wait_consumer(struct consumer_data *consumer_data)
> +{
> +       pid_t ret;
> +       int status;
> +
> +       if (consumer_data->pid <= 0) {
> +               return;
> +       }
> +
> +       DBG("Waiting for complete teardown of consumerd (PID: %d)",
> +                       consumer_data->pid);
> +       ret = waitpid(consumer_data->pid, &status, 0);
> +       if (ret == -1) {
> +               PERROR("consumerd waitpid pid: %d", consumer_data->pid)
> +       }
> +       if (!WIFEXITED(status)) {
> +               ERR("consumerd termination with error: %d",
> +                               WEXITSTATUS(ret));
> +       }
> +       consumer_data->pid = 0;
> +}
> +
> +/*
>   * Cleanup the session daemon's data structures.
>   */
>  static void sessiond_cleanup(void)
> @@ -680,6 +708,11 @@ static void sessiond_cleanup(void)
>                 }
>         }
>
> +       wait_consumer(&kconsumer_data);
> +       wait_consumer(&ustconsumer64_data);
> +       wait_consumer(&ustconsumer32_data);
> +
> +
>         DBG("Cleaning up all agent apps");
>         agent_app_ht_clean();
>
> @@ -1497,7 +1530,6 @@ error:
>
>         unlink(consumer_data->err_unix_sock_path);
>         unlink(consumer_data->cmd_unix_sock_path);
> -       consumer_data->pid = 0;
>         pthread_mutex_unlock(&consumer_data->lock);
>
>         /* Cleanup metadata socket mutex. */
> --
> 2.1.4
>



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