Re: [PATCH v2] core: workqueue: return on workqueue recursion

[Oleg Nesterov <oleg@redhat.com>]

On 02/04, Simon Kagstrom wrote:
>
> When the workqueue is flushed from workqueue context (recursively), the
> system enters a strange state where things at random (dependent on the
> global workqueue) start misbehaving. For example, for us the console and
> logins locks up while the web server continues running.
>
> The system becomes unstable since the workqueue barrier locks the
> workqueue. This patch instead returns if the workqueue is flushed
> recursively, which keeps the workqueue alive but warns.
>
> Signed-off-by: Simon Kagstrom <simon.kagstrom@netinsight.net>

Acked-by: Oleg Nesterov <oleg@redhat.com>

> ---
> ChangeLog:
> 	* Instead of BUG_ON, warn and return on recursive calls as suggested
> 	  by Oleg Nesterov and Tejun Hao
>
>  kernel/workqueue.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index dee4865..49f8fa7 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -482,7 +482,8 @@ static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
>  	int active = 0;
>  	struct wq_barrier barr;
>
> -	WARN_ON(cwq->thread == current);
> +	if (WARN_ON(cwq->thread == current))
> +		return 1;
>
>  	spin_lock_irq(&cwq->lock);
>  	if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
> --
> 1.6.0.4
>