linux-kernel - Re: [PATCH 1/2] tracing/perf: Prevent double unregister of perf probes

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Message-ID: <2bbdd0fa-58cf-41ad-a297-125987ff2fbc@quicinc.com>
Date: Fri, 18 Jul 2025 13:05:48 +0530
From: Aditya Chillara <quic_achillar@...cinc.com>
To: Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra
	<peterz@...radead.org>
CC: Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] tracing/perf: Prevent double unregister of perf
 probes

[ Added Peter for 7ef5aa081f98 and kernel/events/core.c ]

On 7/9/2025 10:48 PM, Steven Rostedt wrote:
> On Wed, 9 Jul 2025 22:20:00 +0530
> Aditya Chillara <quic_achillar@...cinc.com> wrote:
> 
>> The exact problem was introduced by:
>> https://github.com/torvalds/linux/commit/7ef5aa081f989ecfecc1df02068a80aebbd3ec31
>> (perf/core: Simplify the perf_event_alloc() error path)
>> where __free_event was calling event->destroy() even though it would
>> have been called by perf_try_init_event in case it failed.
> 
> Then I rather have it trigger a WARN_ON() and disable that event
> permanently until reboot. It's a bug, no need to continue using the
> event when it's in an a bad state.

perf_trace_event_unreg is called only in event->destroy(), and this is
called in event free path; either after the event is removed from its
context, or before the event is installed in a context. I believe there
is no need to explicitly disable the perf event here because it must
have been disabled already. Please let me know if I'm missing anything.

Best Regards,
Aditya