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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Jun 2025 09:20:41.7540 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 12ec1221-f666-4226-96bb-08dda27fe97d 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: AM2PEPF0001C713.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV2PR08MB9349 Hi David, > > > > > > > > > > Also, your patch couldn't solve a problem describe in > > > > > commit a3c3c6667("perf/core: Fix child_total_time_enabled accounting bug at task exit") > > > > > for INCATIVE event's total_enable_time. > > > > > > > > I do not think so. > > > > Correct me if I am making silly mistakes, > > > > The patch, https://lore.kernel.org/lkml/20250603032651.3988-1-00107082@163.com/ > > > > calls perf_event_set_state() based on DETACH_EXIT flag, which cover the INACTIVE state, right? > > > > If DETACH_EXIT is not used for this purpose? Then why should it exist at the first place? > > > > I think I does not revert the purpose of commit a3c3c6667.....But I could be wrong > > > > Would you show a call path where DETACH_EXIT is not set, but the changes in commit a3c3c6667 is still needed? > > > > > > > > Sorry for my bad explaination without detail. > > > > Think about cpu specific event and closed by task. > > > > If there is specific child cpu event specified in cpu 0. > > > > 1. cpu 0 -> active > > > > 2. scheulded to cpu1 -> inactive > > > > 3. close the cpu event from parent -> inactive close > > > > > > > > Can be failed to count total_enable_time. > > > > > > Is this explaining the purpose of commit a3c3c6667 ? > > > I am not arguing with it. And I also not suggest reverting it. (it is just that reverting it can fix the kernel panic.) > > > > In commit a3c3c6667, I explain the specific case but not with above > > case. But the commit's purpose is "account total_enable_time" properly. > > > > > > And also, considering the your patch, for DETACH_EXIT case, > > > > If it changes the state before list_del_event() that wouldn't disable > > > > related to the cgroup. So it would make cpuctx->cgrp pointer could be dangled > > > > as patch describe... > > > No, I don't think so. > > > change state before list_del_event(), this is the same behavior before commit a3c3c6667, right? > > > And no such kernel panic happened before commit a3c3c6667. > > Oh! I was wrong, before commit a3c3c6667, "change state" happened *after* list_del_event() > > > > That's why list_del_event() handle the perf_cgroup_disable() before the > > commit a3c3c6667. However because of *my mistake*, I've forget to > > perf_cgroup_disable() properly before change the event state. > > Yes, your patch can make avoid the panic since as soon as exit, > > the event->cgrp switched. > > I cannot agree with the reasoning, > The panic dose not happened when exit, it happened when reboot/shutdown. > (I close perf_event_open before reboot) > > > > However, as I said, the INACTIVE event could be failed to count > >total_enable_time. > > > > So, set event should be occured before list_del_event(). > >And since it's event->state change on remove. > >It shouldn't have any side effect the state change isn't cause of your > > panic. But missed perf_cgroup_disable(). > > Any procedure to bring out the impact of this missed perf_cgroup_disable()? > My system seems all normal, where should I check it? Here is possible senario: 1. perf event open with cgroup. 2. perf event open with cpu event (no cgroup). 3. above task sets the cpuctx->cgrp the same to (1). 3. close (1) events. here, perf_cgroup_event_disable() isn't called, cpuctx->cgrp still point the cgroup. 4. by other task, the cgroup and is destroied. 5. close (2) events. here, it is last event, in __perf_remove_from_context() and last event, it calls update_cgrp_time_from_cpuctx(), And this refers invalid pointer. > But to fix it, isn't following change less aggressive? > event_sched_out(event, ctx); > - perf_event_set_state(event, min(event->state, state)); > if (flags & DETACH_GROUP) > perf_group_detach(event); > if (flags & DETACH_CHILD) > perf_child_detach(event); > list_del_event(event, ctx); > + perf_event_set_state(event, min(event->state, state)); If perf_child_detach() is called first and perf_event_set_state() call, since the parent is removed in perf_child_detatced, It would be failed to account the total_enable_time which caculating child_event's enable_time too. Thanks -- Sincerely, Yeoreum Yun