Re: [PATCH 1/1] perf/core: fix dangling cgroup pointer in cpuctx

[Leo Yan <leo.yan@arm.com>]

On Wed, Jun 04, 2025 at 03:58:01PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 04, 2025 at 11:18:21AM +0100, Leo Yan wrote:
> 
> > Totally agree. The comment would be very useful!
> 
> I have the below. Let me go read your email in more than 2 seconds to
> see if I should amend things.
> 
> I'm not sure doing the INACTIVE->INACTIVE cycle in the ASCII art is
> going to make it clearer, might leave that off. But yeah, possible.
> 
> ---
> 
> Subject: perf: Add comment to enum perf_event_state
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Wed Jun  4 10:21:38 CEST 2025
> 
> Better describe the event states.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  include/linux/perf_event.h |   42 ++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 40 insertions(+), 2 deletions(-)
> 
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -635,8 +635,46 @@ struct perf_addr_filter_range {
>  	unsigned long			size;
>  };
>  
> -/**
> - * enum perf_event_state - the states of an event:
> +/*
> + * The normal states are:
> + *
> + *            ACTIVE    --.
> + *               ^        |
> + *               |        |
> + *       sched_{in,out}() |
> + *               |        |
> + *               v        |
> + *      ,---> INACTIVE  --+ <-.
> + *      |                 |   |
> + *      |                {dis,en}able()
> + *   sched_in()           |   |
> + *      |       OFF    <--' --+
> + *      |                     |
> + *      `--->  ERROR    ------'
> + *
> + * That is:
> + *
> + * sched_in:       INACTIVE          -> {ACTIVE,ERROR}
> + * sched_out:      ACTIVE            -> INACTIVE
> + * disable:        {ACTIVE,INACTIVE} -> OFF
> + * enable:         {OFF,ERROR}       -> INACTIVE
> + *
> + * Where {OFF,ERROR} are disabled states.
> + *
> + * Then we have the {EXIT,REVOKED,DEAD} states which are various shades of
> + * defunct events:
> + *
> + *  - EXIT means task that the even was assigned to died, but child events
> + *    still live, and further children can still be created. But the event
> + *    itself will never be active again. It can only transition to
> + *    {REVOKED,DEAD};
> + *
> + *  - REVOKED means the PMU the event was associated with is gone; all
> + *    functionality is stopped but the event is still alive. Can only
> + *    transition to DEAD;
> + *
> + *  - DEAD event really is DYING tearing down state and freeing bits.
> + *

LGTM:

Reviewed-by: Leo Yan <leo.yan@arm.com>

>   */
>  enum perf_event_state {
>  	PERF_EVENT_STATE_DEAD		= -5,