Re: [PATCH 1/4] pm/fan: drop the fan lock in fan_update() before rescheduling

[Martin Peres <martin.peres-GANU6spQydw@public.gmane.org>]

Le 24/03/2014 02:03, Martin Peres a écrit :
> From: Martin Peres <martin.peres@labri.fr>
>
> This should fix a deadlock that has been reported to us where fan_update()
> would hold the fan lock and try to grab the alarm_program_lock to reschedule
> an update. On an other CPU, the alarm_program_lock would have been taken
> before calling fan_update(), leading to a deadlock.
>
> We should Cc: <stable@vger.kernel.org> # 3.9+
>
> Reported-by: Marcin Slusarz <marcin.slusarz@gmail.com>
> Tested-by: Timothée Ravier <tim@siosm.fr>

Tested-by: Boris Fersing (IRC nick fersingb, email is private)

> Signed-off-by: Martin Peres <martin.peres@free.fr>
> ---
>   nvkm/subdev/therm/fan.c | 19 +++++++++++++------
>   1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/nvkm/subdev/therm/fan.c b/nvkm/subdev/therm/fan.c
> index 95f6129..29d4c41 100644
> --- a/nvkm/subdev/therm/fan.c
> +++ b/nvkm/subdev/therm/fan.c
> @@ -54,8 +54,10 @@ nouveau_fan_update(struct nouveau_fan *fan, bool immediate, int target)
>
>   	/* check that we're not already at the target duty cycle */
>   	duty = fan->get(therm);
> -	if (duty == target)
> -		goto done;
> +	if (duty == target) {
> +		spin_unlock_irqrestore(&fan->lock, flags);
> +		return 0;
> +	}
>
>   	/* smooth out the fanspeed increase/decrease */
>   	if (!immediate && duty >= 0) {
> @@ -73,8 +75,15 @@ nouveau_fan_update(struct nouveau_fan *fan, bool immediate, int target)
>
>   	nv_debug(therm, "FAN update: %d\n", duty);
>   	ret = fan->set(therm, duty);
> -	if (ret)
> -		goto done;
> +	if (ret) {
> +		spin_unlock_irqrestore(&fan->lock, flags);
> +		return ret;
> +	}
> +
> +	/* fan speed updated, drop the fan lock before grabbing the
> +	 * alarm-scheduling lock and risking a deadlock
> +	 */
> +	spin_unlock_irqrestore(&fan->lock, flags);
>
>   	/* schedule next fan update, if not at target speed already */
>   	if (list_empty(&fan->alarm.head) && target != duty) {
> @@ -92,8 +101,6 @@ nouveau_fan_update(struct nouveau_fan *fan, bool immediate, int target)
>   		ptimer->alarm(ptimer, delay * 1000 * 1000, &fan->alarm);
>   	}
>
> -done:
> -	spin_unlock_irqrestore(&fan->lock, flags);
>   	return ret;
>   }
>
>

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