[syslog-ng] [PATCH] afmongodb: Fix a race condition in the queue handling.

[Balazs Scheidler]

On Thu, 2011-12-29 at 14:41 +0100, Gergely Nagy wrote:
> There is a race condition between afmongodb_dd_queue() and
> afmongodb_worker_insert(), that can trigger an assertion when the rate
> of incoming messages is very high.
> 
> The scenario that triggers this is like this:
> 
> * We receive a message, put it in our internal queue, and notify the
>   worker thread.
> * The worker thread resets the queue's parallel_push.
> * We receive another message, notice that the queue is empty, so we
>   insert it, and set parallel_push at the same time.
> * The worker thread tries to pop the queue's head, but that triggers
>   an assert, because parallel_push is set.
> 
> The root cause of the problem is that afmongodb_dd_queue() modifies
> the queue without locking the queue_mutex. This patch corrects that
> problem.
> 
> Reported-By: Costa Farber <costaf at wix.com>
> Signed-off-by: Gergely Nagy <algernon at balabit.hu>
> ---
>  modules/afmongodb/afmongodb.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/modules/afmongodb/afmongodb.c b/modules/afmongodb/afmongodb.c
> index cbd0d16..a88aeaa 100644
> --- a/modules/afmongodb/afmongodb.c
> +++ b/modules/afmongodb/afmongodb.c
> @@ -530,7 +530,9 @@ afmongodb_dd_queue(LogPipe *s, LogMessage *msg, const LogPathOptions *path_optio
>    g_mutex_lock(self->suspend_mutex);
>    if (queue_was_empty && !self->writer_thread_suspended)
>      {
> +      g_mutex_lock(self->queue_mutex);
>        log_queue_set_parallel_push(self->queue, 1, afmongodb_dd_queue_notify, self, NULL);
> +      g_mutex_unlock(self->queue_mutex);
>      }
>    g_mutex_unlock(self->suspend_mutex);
>  }

Thanks Gergely, applied to 3.3.

-- 
Bazsi