[Intel-gfx] [PATCH] drm/i915/execlists: Assert tasklet is locked for process_csb()

[Tvrtko Ursulin]

On 13/10/2019 20:31, Chris Wilson wrote:
> We rely on only the tasklet being allowed to call into process_csb(), so
> assert that is locked when we do. As the tasklet uses a simple bitlock,
> there is no strong lockdep checking so we must make do with a plain
> assertion that the tasklet is running and assume that we are the
> tasklet!
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_lrc.c | 1 +
>   drivers/gpu/drm/i915/i915_gem.h     | 5 +++++
>   2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 8be9e69d5718..ab20433182d1 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1984,6 +1984,7 @@ static void process_csb(struct intel_engine_cs *engine)
>   	u8 head, tail;
>   
>   	GEM_BUG_ON(USES_GUC_SUBMISSION(engine->i915));
> +	GEM_BUG_ON(!tasklet_is_locked(&execlists->tasklet));

I see some reset paths calling process_csb which looks like a problem 
for this assert.

Regards,

Tvrtko

>   
>   	/*
>   	 * Note that csb_write, csb_status may be either in HWSP or mmio.
> diff --git a/drivers/gpu/drm/i915/i915_gem.h b/drivers/gpu/drm/i915/i915_gem.h
> index db20d2b0842b..f6f9675848b8 100644
> --- a/drivers/gpu/drm/i915/i915_gem.h
> +++ b/drivers/gpu/drm/i915/i915_gem.h
> @@ -86,6 +86,11 @@ static inline void tasklet_lock(struct tasklet_struct *t)
>   		cpu_relax();
>   }
>   
> +static inline bool tasklet_is_locked(const struct tasklet_struct *t)
> +{
> +	return test_bit(TASKLET_STATE_RUN, &t->state);
> +}
> +
>   static inline void __tasklet_disable_sync_once(struct tasklet_struct *t)
>   {
>   	if (!atomic_fetch_inc(&t->count))
>