linux-kernel - Re: [PATCH v2 24/24] perf: Make perf_pmu

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Message-ID: <72078a3d-4b19-4aa9-bed7-f95362b6265a@amd.com>
Date: Mon, 10 Feb 2025 12:09:18 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: "mingo@...nel.org" <mingo@...nel.org>,
 "lucas.demarchi@...el.com" <lucas.demarchi@...el.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "willy@...radead.org" <willy@...radead.org>,
 "acme@...nel.org" <acme@...nel.org>,
 "namhyung@...nel.org" <namhyung@...nel.org>,
 "mark.rutland@....com" <mark.rutland@....com>,
 "alexander.shishkin@...ux.intel.com" <alexander.shishkin@...ux.intel.com>,
 "jolsa@...nel.org" <jolsa@...nel.org>,
 "irogers@...gle.com" <irogers@...gle.com>,
 "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
 "kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>,
 Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH v2 24/24] perf: Make perf_pmu_unregister() useable

Hi Peter,

> @@ -1737,7 +1742,7 @@ static inline bool needs_branch_stack(st
>  
>  static inline bool has_aux(struct perf_event *event)
>  {
> -	return event->pmu->setup_aux;
> +	return event->pmu && event->pmu->setup_aux;
>  }

this ...

> @@ -6412,7 +6444,7 @@ static void perf_mmap_open(struct vm_are
>  	if (vma->vm_pgoff)
>  		atomic_inc(&event->rb->aux_mmap_count);
>  
> -	if (event->pmu->event_mapped)
> +	if (event->pmu && event->pmu->event_mapped)
>  		event->pmu->event_mapped(event, vma->vm_mm);
>  }
>  
> @@ -6435,7 +6467,8 @@ static void perf_mmap_close(struct vm_ar
>  	unsigned long size = perf_data_size(rb);
>  	bool detach_rest = false;
>  
> -	if (event->pmu->event_unmapped)
> +	/* FIXIES vs perf_pmu_unregister() */
> +	if (event->pmu && event->pmu->event_unmapped)
>  		event->pmu->event_unmapped(event, vma->vm_mm);

these two ...

> @@ -6837,7 +6880,7 @@ static int perf_mmap(struct file *file,
>  	if (!ret)
>  		ret = map_range(rb, vma);
>  
> -	if (!ret && event->pmu->event_mapped)
> +	if (!ret && event->pmu && event->pmu->event_mapped)
>  		event->pmu->event_mapped(event, vma->vm_mm);

... and this one.

There is no serialization at all these places. i.e. event->pmu can become
NULL in between two checks.

  CPU0:            event->pmu = NULL
                         |
                         V
  CPU1:   if (event->pmu && event->pmu->blahblah())

Thanks,
Ravi