Re: [PATCH 5/6] drm/i915/breadcrumbs: Assert that we do not shortcut the current bottom-half

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 15/03/2017 14:01, Chris Wilson wrote:
> We need to ensure that we always serialize updates to the bottom-half
> using the breadcrumbs.irq_lock so that we don't race with a concurrent
> interrupt handler. This is most important just prior to leaving the
> waiter (when the intel_wait will be overwritten), so make sure we are
> not the current bottom-half when skipping the irq locks.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_breadcrumbs.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> index ebcb595001fc..d10148567dbc 100644
> --- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> @@ -287,6 +287,7 @@ static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b,
>  					      struct intel_wait *wait)
>  {
>  	lockdep_assert_held(&b->rb_lock);
> +	GEM_BUG_ON(b->irq_wait == wait);
>
>  	/* This request is completed, so remove it from the tree, mark it as
>  	 * complete, and *then* wake up the associated task.
> @@ -517,8 +518,10 @@ void intel_engine_remove_wait(struct intel_engine_cs *engine,
>  	 * the tree by the bottom-half to avoid contention on the spinlock
>  	 * by the herd.
>  	 */
> -	if (RB_EMPTY_NODE(&wait->node))
> +	if (RB_EMPTY_NODE(&wait->node)) {
> +		GEM_BUG_ON(READ_ONCE(b->irq_wait) == wait);
>  		return;
> +	}
>
>  	spin_lock_irq(&b->rb_lock);
>  	__intel_engine_remove_wait(engine, wait);
>

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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