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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Jun 2025 10:07:30.7703 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 3d6acb2a-6c1c-4a51-47ca-08dda34f9e36 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AM4PEPF00027A5E.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DU0PR08MB8230 Hi Peter, > On Tue, Jun 03, 2025 at 04:44:14PM +0200, Peter Zijlstra wrote: > > On Tue, Jun 03, 2025 at 03:00:40PM +0100, Leo Yan wrote: > > > > > > + if (event->state > PERF_EVENT_STATE_OFF) > > > > + perf_cgroup_event_disable(event, ctx); > > > > + > > > > > > As we discussed, seems to me, the issue is caused by an ambigous state > > > machine transition: > > > > > > When a PMU event state is PERF_EVENT_STATE_EXIT, the current code does > > > not transite the state to PERF_EVENT_STATE_OFF. As a result, the > > > list_del_event() function skips to clean up cgroup pointer for non OFF > > > states. This is different from the code prior to the commit a3c3c6667, > > > which transits states EXIT -> INACTIVE -> OFF. > > > > Right. > > > > > My suggestion is not reliable. Roughly read code, except for the > > > PERF_EVENT_STATE_EXIT case, I think other error cases should also clean > > > up the cgroup pointer. The reason is I don't see other places to > > > clean up the cgroup pointer for these error cases: > > > > > > PERF_EVENT_STATE_REVOKED > > > PERF_EVENT_STATE_DEAD > > > > Those should be done here; on the first transition into these states. > > > > > Only in the PERF_EVENT_STATE_ERROR state, we don't need to cleanup > > > cgroup as this has already been handled in merge_sched_in(). > > > > > > So a correct condition would be: > > > > > > if (event->state > PERF_EVENT_STATE_OFF || > > > event->state <= PERF_EVENT_STATE_EXIT) > > > perf_cgroup_event_disable(event, ctx); > > > > I'm too tired to get my head straight. I'll look tomorrow. > > > Right; had a sleep. Lets do this :-) > > > So 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 'disable' and have this perf_cgroup_event_disable() > called. > > Then we have {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}; I have a slight quetions. after parent event set EXIT, Does EXIT event should be inherited? for example parent task(0, ...) -> parent_event(0, parent_event:NULL) ` child_task(1, parent:0) -> child_event(1, parent_event:0) ` child_task(2, parent:1) -> child_event(2, parent_event:0) In this case when parent task(0) is exited, parent->event will be set as EXIT state. But suppose the child_task(2) try to fork (child_task3) and inherit the event (create child_event(3, parent_event:0), and at the fork, forking can observe the parent event state as "EXIT". In thie situation why child_event(3, parent_event:0) should be created for child_task(3)? > - 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. > > And now we have the sitation that __perf_remove_from_context() can do: > > {ACTIVE,INACTIVE,OFF,ERROR} -> {OFF,EXIT,REVOKED,DEAD} > > Where the {OFF,ERROR} -> * transition already have > perf_cgroup_event_disable(), but the {ACTIVE,INACTIVE} -> * part has > not. > > The condition: > > if (event->state > PERF_EVENT_STATE_OFF) > > captures exactly that {ACTIVE,INACTIVE} that still needs the cgroup > disable. Every other state is already a disabled state. > > > Agreed? > > Also, I should probably stick most of all this in a comment somewhere. -- Sincerely, Yeoreum Yun