Re: [PATCH 1/2] drm/i915: Pull sync_scru for device reset outside of wedge_mutex

From: Mika Kuoppala <mika.kuoppala@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 1/2] drm/i915: Pull sync_scru for device reset outside of wedge_mutex
Date: Mon, 11 Feb 2019 17:09:48 +0200	[thread overview]
Message-ID: <87r2ce1hvn.fsf@gaia.fi.intel.com> (raw)
In-Reply-To: <20190211135040.1234-1-chris@chris-wilson.co.uk>

Chris Wilson <chris@chris-wilson.co.uk> writes:

> We need to flush our srcu protecting resources about to be clobbered
> by the reset, inside of our timer failsafe but outside of the
> error->wedge_mutex, so that the failsafe can run in case the
> synchronize_srcu() takes too long (hits a shrinker deadlock?).
>
> Fixes: 72eb16df010a ("drm/i915: Serialise resets with wedging")
> References: https://bugs.freedesktop.org/show_bug.cgi?id=109605
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reset.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_reset.c b/drivers/gpu/drm/i915/i915_reset.c
> index 9494b015185a..c2b7570730c2 100644
> --- a/drivers/gpu/drm/i915/i915_reset.c
> +++ b/drivers/gpu/drm/i915/i915_reset.c
> @@ -941,9 +941,6 @@ static int do_reset(struct drm_i915_private *i915, unsigned int stalled_mask)
>  {
>  	int err, i;
>  
> -	/* Flush everyone currently using a resource about to be clobbered */
> -	synchronize_srcu(&i915->gpu_error.reset_backoff_srcu);
> -
>  	err = intel_gpu_reset(i915, ALL_ENGINES);
>  	for (i = 0; err && i < RESET_MAX_RETRIES; i++) {
>  		msleep(10 * (i + 1));
> @@ -1140,6 +1137,9 @@ static void i915_reset_device(struct drm_i915_private *i915,
>  	i915_wedge_on_timeout(&w, i915, 5 * HZ) {
>  		intel_prepare_reset(i915);
>  
> +		/* Flush everyone using a resource about to be clobbered */
> +		synchronize_srcu(&error->reset_backoff_srcu);
> +

Do we easily see which one it will be? This one or
the block below to timeout on wedge?

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

>  		mutex_lock(&error->wedge_mutex);
>  		i915_reset(i915, engine_mask, reason);
>  		mutex_unlock(&error->wedge_mutex);
> -- 
> 2.20.1
>
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