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

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Message-ID: <20190120222140.GA6626@jaya.lan>
Date:   Sun, 20 Jan 2019 23:21:40 +0100
From:   Anisse Astier <anisse@...ier.eu>
To:     Phil Elwell <phil@...pberrypi.org>
Cc:     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
Subject: Re: [PATCH] staging: vchiq: Fix local event signalling

Hi Phil,

On Fri, Jan 11, 2019 at 11:34:53AM +0000, Phil Elwell wrote:
> 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.

This fixes an issue I've had on linux 5.0-pre to 5.0-rc2+: the
bcm2835-audio driver would block on close, and then nothing would work
until the process was killed. Sample log:

bcm2835_audio bcm2835_audio: failed to close VCHI service connection (status=1)

> 
> Fixes: 852b2876a8a8 ("staging: vchiq: rework remove_event handling")
> Signed-off-by: Phil Elwell <phil@...pberrypi.org>

Tested-by: Anisse Astier <anisse@...ier.eu>


Regards,

Anisse