[Intel-gfx] [PATCH 1/2] drm/i915/guc: Use correct lock for accessing guc->mmio_msg

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-11-20 09:56:35)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Guc->mmio_msg is set under the guc->irq_lock in guc_get_mmio_msg so it
> should be consumed under the same lock from guc_handle_mmio_msg.
> 
> I am not sure if the overall flow here makes complete sense but at least
> the correct lock is now used.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> ---
>  drivers/gpu/drm/i915/gt/uc/intel_uc.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc.c b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
> index 4e6070e95fe9..220626c3ad81 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_uc.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
> @@ -175,19 +175,15 @@ static void guc_get_mmio_msg(struct intel_guc *guc)
>  
>  static void guc_handle_mmio_msg(struct intel_guc *guc)
>  {
> -       struct drm_i915_private *i915 = guc_to_gt(guc)->i915;
> -
>         /* we need communication to be enabled to reply to GuC */
>         GEM_BUG_ON(!guc_communication_enabled(guc));
>  
> -       if (!guc->mmio_msg)
> -               return;
> -
> -       spin_lock_irq(&i915->irq_lock);
> -       intel_guc_to_host_process_recv_msg(guc, &guc->mmio_msg, 1);
> -       spin_unlock_irq(&i915->irq_lock);
> -
> -       guc->mmio_msg = 0;
> +       spin_lock_irq(&guc->irq_lock);
> +       if (guc->mmio_msg) {
> +               intel_guc_to_host_process_recv_msg(guc, &guc->mmio_msg, 1);
> +               guc->mmio_msg = 0;
> +       }
> +       spin_unlock_irq(&guc->irq_lock);

Based on just looking at mmio_msg, the locking should be guc->irq_lock, and
guc->mmio_msg = 0 should be pulled under the lock.

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris