[PATCH v2 1/2] powerpc/pseries: Avoid blocking rtas polling handling multiple PRRN events

[Nathan Fontenot]

On 07/17/2018 02:40 PM, John Allen wrote:
> When a PRRN event is being handled and another PRRN event comes in, the
> second event will block rtas polling waiting on the first to complete,
> preventing any further rtas events from being handled. This can be
> especially problematic in case that PRRN events are continuously being
> queued in which case rtas polling gets indefinitely blocked completely.
> 
> This patch introduces a mutex that prevents any subsequent PRRN events from
> running while there is a prrn event being handled, allowing rtas polling to
> continue normally.
> 
> Signed-off-by: John Allen <jallen at linux.ibm.com>

Reviewed-by: Nathan Fontenot <nfont at linux.vnet.ibm.com>

> ---
> v2:
>    -Unlock prrn_lock when PRRN operations are complete, not after handler is
>     scheduled.
>    -Remove call to flush_work, the previous broken method of serializing
>     PRRN events.
> ---
>   arch/powerpc/kernel/rtasd.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/rtasd.c b/arch/powerpc/kernel/rtasd.c
> index 44d66c33d59d..845fc5aec178 100644
> --- a/arch/powerpc/kernel/rtasd.c
> +++ b/arch/powerpc/kernel/rtasd.c
> @@ -35,6 +35,8 @@
> 
>   static DEFINE_SPINLOCK(rtasd_log_lock);
> 
> +static DEFINE_MUTEX(prrn_lock);
> +
>   static DECLARE_WAIT_QUEUE_HEAD(rtas_log_wait);
> 
>   static char *rtas_log_buf;
> @@ -284,15 +286,17 @@ static void prrn_work_fn(struct work_struct *work)
>   	 */
>   	pseries_devicetree_update(-prrn_update_scope);
>   	numa_update_cpu_topology(false);
> +	mutex_unlock(&prrn_lock);
>   }
> 
>   static DECLARE_WORK(prrn_work, prrn_work_fn);
> 
>   static void prrn_schedule_update(u32 scope)
>   {
> -	flush_work(&prrn_work);
> -	prrn_update_scope = scope;
> -	schedule_work(&prrn_work);
> +	if (mutex_trylock(&prrn_lock)) {
> +		prrn_update_scope = scope;
> +		schedule_work(&prrn_work);
> +	}
>   }
> 
>   static void handle_rtas_event(const struct rtas_error_log *log)
>