Re: [PATCH 2/2] perf: Add checks to prevent null ptr access

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 9/5/2026 2:16 AM, Vinay Belgaumkar wrote:
> Sashiko recommended some additional checks to prevent null pointer
> access. Check for revoked states inside perf_event_read_local(), as
> the pmu event may have already been freed at this point. Add a null

Could you please show where perf_event_read_local() could be called after
the event is revoked?

BTW, the prefix should be "perf/core:" instead of "perf:" by following
current naming convention.

Thanks.


> check inside __perf_event_read_cpu() as well before accessing the pmu
> ptr.
>
> Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
> Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
> ---
>  kernel/events/core.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 7777e82aad5e..059f82f0cadd 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4788,14 +4788,19 @@ static inline const struct cpumask *perf_scope_cpu_topology_cpumask(unsigned int
>  
>  static int __perf_event_read_cpu(struct perf_event *event, int event_cpu)
>  {
> +	struct pmu *pmu = READ_ONCE(event->pmu);
>  	int local_cpu = smp_processor_id();
>  	u16 local_pkg, event_pkg;
>  
>  	if ((unsigned)event_cpu >= nr_cpu_ids)
>  		return event_cpu;
>  
> +	if (!pmu)
> +		return -ENODEV;
> +
>  	if (event->group_caps & PERF_EV_CAP_READ_SCOPE) {
> -		const struct cpumask *cpumask = perf_scope_cpu_topology_cpumask(event->pmu->scope, event_cpu);
> +		const struct cpumask *cpumask = perf_scope_cpu_topology_cpumask(pmu->scope,
> +										event_cpu);
>  
>  		if (cpumask && cpumask_test_cpu(local_cpu, cpumask))
>  			return local_cpu;
> @@ -4917,6 +4922,11 @@ int perf_event_read_local(struct perf_event *event, u64 *value,
>  		goto out;
>  	}
>  
> +	if (READ_ONCE(event->state) <= PERF_EVENT_STATE_REVOKED) {
> +		ret = -ENODEV;
> +		goto out;
> +	}
> +
>  	/*
>  	 * Get the event CPU numbers, and adjust them to local if the event is
>  	 * a per-package event that can be read locally