Re: [PATCH 6/6] drm/i915: Only call tasklet_kill() on the first prepare_reset

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

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

> tasklet_kill() will spin waiting for the current tasklet to be executed.
> However, if tasklet_disable() has been called, then the tasklet is never
> executed but permanently put back onto the runlist until
> tasklet_enable() is called. Ergo, we cannot use tasklet_kill() inside a
> disable/enable pair. This is the case when we call set-wedge from inside
> i915_reset(), and another request was submitted to us concurrent to the
> reset.
>
> Fixes: 963ddd63c314 ("drm/i915: Suspend submission tasklets around wedging")
> 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 | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 3b44952e089f..e75af06904b7 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2941,7 +2941,8 @@ i915_gem_reset_prepare_engine(struct intel_engine_cs *engine)
>  	 * Turning off the execlists->tasklet until the reset is over
>  	 * prevents the race.
>  	 */
> -	tasklet_kill(&engine->execlists.tasklet);
> +	if (!atomic_read(&engine->execlists.tasklet.count))
> +		tasklet_kill(&engine->execlists.tasklet);

As discussed in irc, this might warrant  comment that it is
our tasklet of which count we are racily investigating here,
so the race does not matter in the path we avoid killing.

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

>  	tasklet_disable(&engine->execlists.tasklet);
>  
>  	/*
> -- 
> 2.16.2
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