linux-kernel - Re: [PATCH] perf: Fix lockdep warning in perf_event_throttle

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Message-ID: <8dd3659d-8395-49da-94c0-3f18880ead1f@linux.intel.com>
Date: Thu, 13 Nov 2025 16:15:15 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Jianhui Zhou <jianhuizz@...com>, peterz@...radead.org, mingo@...hat.com
Cc: acme@...nel.org, namhyung@...nel.org, mark.rutland@....com,
 alexander.shishkin@...ux.intel.com, jolsa@...nel.org, irogers@...gle.com,
 adrian.hunter@...el.com, james.clark@...aro.org, jonaszhou@...oxin.com,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 syzbot+a945e9d15c8a49a7a7f0@...kaller.appspotmail.com
Subject: Re: [PATCH] perf: Fix lockdep warning in perf_event_throttle_group


On 11/12/2025 8:34 PM, Jianhui Zhou wrote:
> When perf samples a tracepoint like trace_lock_acquire with high
> frequency, it can trigger a WARN_ON in perf_event_throttle_group()
> due to lockdep assertion failure in for_each_sibling_event().
>
> The issue is that for_each_sibling_event() requires either:
> 1. Holding ctx->mutex, OR
> 2. Having IRQs disabled (since ctx->lock is IRQ-safe)
>
> The call trace shows the problematic path:
> futex_wake
>   lock_acquire
>     trace_lock_acquire
>       perf_trace_lock_acquire
>         perf_tp_event
>           perf_swevent_event
>             __perf_event_overflow
>               __perf_event_account_interrupt
>                 perf_event_throttle_group
>                   for_each_sibling_event [WARN]
>
> In this tracepoint path, IRQs may be enabled and neither ctx->lock
> nor ctx->mutex is held.
>
> The fix adds guard(irqsave)() protection around the sibling list
> iteration in perf_event_throttle_group().
>
> Reported-by: syzbot+a945e9d15c8a49a7a7f0@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/all/69122cb3.a70a0220.22f260.00ff.GAE@google.com/T/
> Signed-off-by: Jianhui Zhou <jianhuizz@...com>
> ---
>  kernel/events/core.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 1fd347da9026..253c514e9452 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -2700,6 +2700,11 @@ static void perf_event_throttle_group(struct perf_event *event)
>  	struct perf_event *sibling, *leader = event->group_leader;
>  
>  	perf_event_throttle(leader);
> +    /*
> +     * Disable IRQs to protect sibling iteration; for_each_sibling_event()
> +     * needs ctx->mutex or IRQs off.
> +     */
> +	guard(irqsave)();

This seems the simplest way to fix the issue although it may bring a slight
overhead if hard irq is already disabled. Thanks.

Reviewed-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>


>  	for_each_sibling_event(sibling, leader)
>  		perf_event_throttle(sibling);
>  }