[PATCH v2] coresight: etm4x: Fix PID tracing when perf is run in an init PID namespace
Julien Meunier
julien.meunier at nokia.com
Fri Oct 25 10:56:02 PDT 2024
Hi Suzuki
On 21/10/2024 14:31, Suzuki K Poulose wrote:
> Hi Julien
>
>
[...]
>
> Unfortunately this is not safe. i.e., event->owner is not guaranteed to
> be stable (even NULL or an invalid pointer) (e.g. kernel created events
> or task exit raced event_start on another CPU).
I expected that event->owner was safe, but you are right. During my
tests, I essentially attached an existing PID executed in an container
(lxc), so I was not able to detect that race condition. I miss to
re-validate all the other usage of CoreSight.
> That said, one thing to note is that the ETM4x driver parses the event
> config in each "event_start" call back, instead of doing once during the
> event_init. If we move this to a onetime parsing at the event_init, with
> additional checks in place (e.g, !is_kernel_event()), we may be able to
> solve it.
Thanks for this suggestion, I will try this approach and provide a v3.
Regards,
Julien
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