Re: [PATCH 2/2] drm/i915/pmu: Use a delayed wakeref put in get_rc6()

["Belgaumkar, Vinay" <vinay.belgaumkar@intel.com>]

On 9/10/2026 11:42 AM, Umesh Nerlige Ramappa wrote:
> get_rc6() has the same runqueue lock deadlock as guc_engine_busyness():
> it is reached from the PMU callbacks, which perf can invoke from the
> scheduler with the runqueue lock held, and intel_gt_pm_put_async() there
> can wake a workqueue worker via try_to_wake_up().
>
> Use intel_gt_pm_put_delay() so the deferred put arms a timer instead.
>
> The remaining async puts in atomic contexts (hrtimer, tasklet, irq_work,
> G2H handlers) cannot run with the runqueue lock held and are left alone.
>
> Fixes: 07779a76ee1f ("drm/i915: Mark up the calling context for intel_wakeref_put()")
> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
> Assisted-by: Claude:claude-opus-5
> ---
>   drivers/gpu/drm/i915/i915_pmu.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> index 1c3bafda9c70..4598d9b5678a 100644
> --- a/drivers/gpu/drm/i915/i915_pmu.c
> +++ b/drivers/gpu/drm/i915/i915_pmu.c
> @@ -229,7 +229,12 @@ static u64 get_rc6(struct intel_gt *gt)
>   	wakeref = intel_gt_pm_get_if_awake(gt);
>   	if (wakeref) {
>   		val = __get_rc6(gt);
> -		intel_gt_pm_put_async(gt, wakeref);
> +		/*
> +		 * We are reached from the perf callbacks, which perf may invoke

rephrase "We are reached"? There is another put_async in 
frequency_sample(). Do we need to update that as well?

Thanks,

Vinay.

> +		 * from the scheduler with the runqueue lock held. Defer the put
> +		 * on a timer so that it can never wake a task from here.
> +		 */
> +		intel_gt_pm_put_delay(gt, wakeref, 1);
>   	}
>   
>   	spin_lock_irqsave(&pmu->lock, flags);