linux-kernel - Re: [PATCH 5/7] drm/i915/pmu: Let resource survive unbind

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Message-ID: <1fa79ff6-9ab0-4b2f-a776-c90f7ce23a80@ursulin.net>
Date: Tue, 23 Jul 2024 08:58:43 +0100
From: Tvrtko Ursulin <tursulin@...ulin.net>
To: Lucas De Marchi <lucas.demarchi@...el.com>,
 intel-gfx@...ts.freedesktop.org, linux-perf-users@...r.kernel.org
Cc: Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
 dri-devel@...ts.freedesktop.org, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] drm/i915/pmu: Let resource survive unbind


On 22/07/2024 22:06, Lucas De Marchi wrote:
> There's no need to free the resources during unbind. Since perf events
> may still access them due to open events, it's safer to free them when
> dropping the last i915 reference.
> 
> Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
> ---
>   drivers/gpu/drm/i915/i915_pmu.c | 21 ++++++++++++++++-----
>   1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> index b5d14dd318e4..8708f905f4f4 100644
> --- a/drivers/gpu/drm/i915/i915_pmu.c
> +++ b/drivers/gpu/drm/i915/i915_pmu.c
> @@ -5,6 +5,7 @@
>    */
>   
>   #include <linux/pm_runtime.h>
> +#include <drm/drm_managed.h>
>   
>   #include "gt/intel_engine.h"
>   #include "gt/intel_engine_pm.h"
> @@ -1152,6 +1153,17 @@ static void free_event_attributes(struct i915_pmu *pmu)
>   	pmu->pmu_attr = NULL;
>   }
>   
> +static void free_pmu(struct drm_device *dev, void *res)
> +{
> +	struct i915_pmu *pmu = res;
> +	struct drm_i915_private *i915 = pmu_to_i915(pmu);
> +
> +	free_event_attributes(pmu);
> +	kfree(pmu->base.attr_groups);
> +	if (IS_DGFX(i915))
> +		kfree(pmu->name);
> +}
> +
>   static int i915_pmu_cpu_online(unsigned int cpu, struct hlist_node *node)
>   {
>   	struct i915_pmu *pmu = hlist_entry_safe(node, typeof(*pmu), cpuhp.node);
> @@ -1302,6 +1314,9 @@ void i915_pmu_register(struct drm_i915_private *i915)
>   	if (ret)
>   		goto err_unreg;
>   
> +	if (drmm_add_action_or_reset(&i915->drm, free_pmu, pmu))
> +		goto err_unreg;

Is i915_pmu_unregister_cpuhp_state missing on this error path?

Regards,

Tvrtko

> +
>   	return;
>   
>   err_unreg:
> @@ -1336,11 +1351,7 @@ void i915_pmu_unregister(struct drm_i915_private *i915)
>   	hrtimer_cancel(&pmu->timer);
>   
>   	i915_pmu_unregister_cpuhp_state(pmu);
> -
>   	perf_pmu_unregister(&pmu->base);
> +
>   	pmu->base.event_init = NULL;
> -	kfree(pmu->base.attr_groups);
> -	if (IS_DGFX(i915))
> -		kfree(pmu->name);
> -	free_event_attributes(pmu);
>   }