linux-kernel - [PATCH] staging: vchiq: Fix local event signalling

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Message-Id: <1547206493-105303-1-git-send-email-phil@raspberrypi.org>
Date:   Fri, 11 Jan 2019 11:34:53 +0000
From:   Phil Elwell <phil@...pberrypi.org>
To:     Eric Anholt <eric@...olt.net>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dominic Braun <inf.braun@....de>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Arnd Bergmann <arnd@...db.de>,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Cc:     Phil Elwell <phil@...pberrypi.org>
Subject: [PATCH] staging: vchiq: Fix local event signalling

Prior to the recent event reworking (see Fixes), thread synchronisation
was implemented using completions, the worker thread being woken with
a call to complete(). The replacement uses waitqueues, which are more
like condition variables in that the waiting thread is only woken if
the condition is true.

When the VPU signals the ARM, it first sets the event's fired flag to
indicate which event is being signalled, but the places in the
ARM-side code where the worker thread is being woken -
remote_event_signal_local via request_poll - did not do so as it
wasn't previously necessary, and since the armed flag was being
cleared this lead to a deadlock.

Fixes: 852b2876a8a8 ("staging: vchiq: rework remove_event handling")
Signed-off-by: Phil Elwell <phil@...pberrypi.org>
---
 drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c
index 9e17ec6..53f5a1c 100644
--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c
@@ -446,6 +446,7 @@ remote_event_wait(wait_queue_head_t *wq, struct remote_event *event)
 static inline void
 remote_event_signal_local(wait_queue_head_t *wq, struct remote_event *event)
 {
+	event->fired = 1;
 	event->armed = 0;
 	wake_up_all(wq);
 }
-- 
2.7.4