Re: [PATCH 1/7] drm/i915: Remove tasklet flush before disable

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

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

> The idea was to try and let the existing tasklet run to completion
> before we began the reset, but it involves a racy check against anything
> else that tries to run the tasklet. Rather than acknowledge and ignore
> the race, let it be and don't try and be too clever.
>
> The tasklet will resume execution after reset (after spinning a bit
> during reset), but before we allow it to resume we will have cleared all
> the pending state.

The disable works only on all future reschedules and
the dequeue is behind timeline lock. But what guards against
the tasklet being currently reading the ports?

-Mika

>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 9 ---------
>  1 file changed, 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 0a2070112b66..0dc369a9ec4d 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3035,16 +3035,7 @@ i915_gem_reset_prepare_engine(struct intel_engine_cs *engine)
>  	 * calling engine->init_hw() and also writing the ELSP.
>  	 * Turning off the execlists->tasklet until the reset is over
>  	 * prevents the race.
> -	 *
> -	 * Note that this needs to be a single atomic operation on the
> -	 * tasklet (flush existing tasks, prevent new tasks) to prevent
> -	 * a race between reset and set-wedged. It is not, so we do the best
> -	 * we can atm and make sure we don't lock the machine up in the more
> -	 * common case of recursively being called from set-wedged from inside
> -	 * i915_reset.
>  	 */
> -	if (!atomic_read(&engine->execlists.tasklet.count))
> -		tasklet_kill(&engine->execlists.tasklet);
>  	tasklet_disable(&engine->execlists.tasklet);
>  
>  	/*
> -- 
> 2.17.0
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