Re: [PATCH] drm/i915: Prevent timeline updates whilst performing reset

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

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

> As the fence may be signaled concurrently from an interrupt on another
> device, it is possible for the list of requests on the timeline to be
> modified as we walk it. Take both (the context's timeline and the global
> timeline) locks to prevent such modifications.
>
> Fixes: 80b204bce8f2 ("drm/i915: Enable multiple timelines")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

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

> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Cc: <drm-intel-fixes@lists.freedesktop.org>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 2d736442c6ab..d94df127d9f6 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2725,6 +2725,7 @@ static void i915_gem_reset_engine(struct intel_engine_cs *engine)
>  	struct drm_i915_gem_request *request;
>  	struct i915_gem_context *incomplete_ctx;
>  	struct intel_timeline *timeline;
> +	unsigned long flags;
>  	bool ring_hung;
>  
>  	if (engine->irq_seqno_barrier)
> @@ -2768,13 +2769,20 @@ static void i915_gem_reset_engine(struct intel_engine_cs *engine)
>  	if (i915_gem_context_is_default(incomplete_ctx))
>  		return;
>  
> +	timeline = i915_gem_context_lookup_timeline(incomplete_ctx, engine);
> +
> +	spin_lock_irqsave(&engine->timeline->lock, flags);
> +	spin_lock(&timeline->lock);
> +
>  	list_for_each_entry_continue(request, &engine->timeline->requests, link)
>  		if (request->ctx == incomplete_ctx)
>  			reset_request(request);
>  
> -	timeline = i915_gem_context_lookup_timeline(incomplete_ctx, engine);
>  	list_for_each_entry(request, &timeline->requests, link)
>  		reset_request(request);
> +
> +	spin_unlock(&timeline->lock);
> +	spin_unlock_irqrestore(&engine->timeline->lock, flags);
>  }
>  
>  void i915_gem_reset(struct drm_i915_private *dev_priv)
> -- 
> 2.11.0
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