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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Jun 2025 07:17:15.9055 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5345a0cf-69b8-49ad-7e1c-08dda26eab45 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: DB1PEPF000509F9.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV1PR08MB10979 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. 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. 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(). Thanks. -- Sincerely, Yeoreum Yun