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

[John Allen]

On Fri, Jul 13, 2018 at 09:22:23AM -0500, 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>
>---
> arch/powerpc/kernel/rtasd.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
>diff --git a/arch/powerpc/kernel/rtasd.c b/arch/powerpc/kernel/rtasd.c
>index 44d66c33d59d..8a72a53d62c0 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;
>@@ -290,9 +292,12 @@ 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)) {
>+		flush_work(&prrn_work);
>+		prrn_update_scope = scope;
>+		schedule_work(&prrn_work);
>+		mutex_unlock(&prrn_lock);

This appears to be bugged. The mutex_unlock should be done elsewhere.  
Will send an updated version.

-John

>+	}
> }
>
> static void handle_rtas_event(const struct rtas_error_log *log)
>-- 
>2.17.1
>