[lttng-dev] [PATCH lttng-tools stable-2.9] Fix: cleanup inactive FDs in the consumer polling thread

[Jérémie Galarneau]

Merged in stable-2.9 with the modified message discussed in the other
thread.

Thanks!
Jérémie

On Thu, Feb 01, 2018 at 02:27:05PM -0500, Jonathan Rajotte wrote:
> From: Julien Desfossez <jdesfossez at efficios.com>
> 
> The data polling thread on the consumer relies on nb_fd and
> consumer_quit to determine if it can exit, but the polling thread is
> also responsible to close inactive streams and there is a case where it
> could exit before it does.
> 
> On consumer teardown (consumer_quit == 1 and all streams hanging up), if
> a relay becomes unreachable, we flag the streams that talk to this relay
> as inactive (CONSUMER_ENDPOINT_INACTIVE) and wakeup the data polling
> thread to close them. If that thread is already busy handling the hangup
> of the remaining streams, it ends up updating the poll array without all
> the inactive streams in it and nb_fd can end up being 0, which makes the
> polling thread exit.
> 
> So we now track the number of inactive streams in update_poll_array()
> and prevent the data polling thread to exit if there are inactive
> streams. That way the write on the data_poll_pipe is received by this
> thread and it can close the inactive streams properly.
> 
> Signed-off-by: Julien Desfossez <jdesfossez at efficios.com>
> Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien at efficios.com>
> ---
>  src/common/consumer/consumer.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/src/common/consumer/consumer.c b/src/common/consumer/consumer.c
> index e379171..814d93e 100644
> --- a/src/common/consumer/consumer.c
> +++ b/src/common/consumer/consumer.c
> @@ -1071,7 +1071,7 @@ int consumer_add_channel(struct lttng_consumer_channel *channel,
>   */
>  static int update_poll_array(struct lttng_consumer_local_data *ctx,
>  		struct pollfd **pollfd, struct lttng_consumer_stream **local_stream,
> -		struct lttng_ht *ht)
> +		struct lttng_ht *ht, int *nb_inactive_fd)
>  {
>  	int i = 0;
>  	struct lttng_ht_iter iter;
> @@ -1083,6 +1083,7 @@ static int update_poll_array(struct lttng_consumer_local_data *ctx,
>  	assert(local_stream);
>  
>  	DBG("Updating poll fd array");
> +	*nb_inactive_fd = 0;
>  	rcu_read_lock();
>  	cds_lfht_for_each_entry(ht->ht, &iter.iter, stream, node.node) {
>  		/*
> @@ -1093,9 +1094,14 @@ static int update_poll_array(struct lttng_consumer_local_data *ctx,
>  		 * just after the check. However, this is OK since the stream(s) will
>  		 * be deleted once the thread is notified that the end point state has
>  		 * changed where this function will be called back again.
> +		 *
> +		 * We track the number of inactive FDs because they still need to be
> +		 * closed by the polling thread after a wakeup on the data_pipe or
> +		 * metadata_pipe.
>  		 */
>  		if (stream->state != LTTNG_CONSUMER_ACTIVE_STREAM ||
>  				stream->endpoint_status == CONSUMER_ENDPOINT_INACTIVE) {
> +			(*nb_inactive_fd)++;
>  			continue;
>  		}
>  		/*
> @@ -2449,6 +2455,8 @@ void *consumer_thread_data_poll(void *data)
>  	struct lttng_consumer_stream **local_stream = NULL, *new_stream = NULL;
>  	/* local view of consumer_data.fds_count */
>  	int nb_fd = 0;
> +	/* Number of FDs with CONSUMER_ENDPOINT_INACTIVE but still open. */
> +	int nb_inactive_fd = 0;
>  	struct lttng_consumer_local_data *ctx = data;
>  	ssize_t len;
>  
> @@ -2505,7 +2513,7 @@ void *consumer_thread_data_poll(void *data)
>  				goto end;
>  			}
>  			ret = update_poll_array(ctx, &pollfd, local_stream,
> -					data_ht);
> +					data_ht, &nb_inactive_fd);
>  			if (ret < 0) {
>  				ERR("Error in allocating pollfd or local_outfds");
>  				lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_POLL_ERROR);
> @@ -2518,7 +2526,7 @@ void *consumer_thread_data_poll(void *data)
>  		pthread_mutex_unlock(&consumer_data.lock);
>  
>  		/* No FDs and consumer_quit, consumer_cleanup the thread */
> -		if (nb_fd == 0 && consumer_quit == 1) {
> +		if (nb_fd == 0 && consumer_quit == 1 && nb_inactive_fd == 0) {
>  			err = 0;	/* All is OK */
>  			goto end;
>  		}
> -- 
> 2.7.4
>