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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Jun 2025 15:06:00.0787 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d30cb376-5b2b-4d3f-f665-08dda2b02698 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: DB5PEPF00014B92.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS2PR08MB8783 Hi Leo, > > On Mon, Jun 02, 2025 at 07:40:49PM +0100, Yeoreum Yun wrote: > > commit a3c3c6667("perf/core: Fix child_total_time_enabled accounting bug at task exit") > > changes the event->state update before list_del_event(). > > This change prevents calling perf_cgroup_event_disable() as a result, > > cpuctx->cgrp can't be cleared properly and point to dangling point of cgroup. > > > > Because of this problem, some machin meets the below panic[0]: > > > > 863.881960] sysved_call_function_sing le+0x4c/0xc0 > > 863.881301] asm_sysvec_call_function_single+0x16/0x20 > > 869.881344] RIP: 0633:0x7f9alcea3367 > > 663.681373] Code: 00 66 99 b8 ff ff ff ff c3 66 .... > > 863.881524] RSP: 002b:00007fffa526fcf8 EFLAGS: 00000246 > > 869.881567] RAX: 0000562060c962d0 RBX: 0000000000000002 RCX: 00007f9a1cff1c60 > > 863.881625] RDX: 00007f9a0c000030 RSI: 00007f9alcff1c60 RDI: 00007f9a1ca91c20 > > 863.081682] RBP: 0000000000000001 R08: 0000000000000000 R09: 00007f9a1d6217a0 > > 869.881740] R10: 00007f9alca91c10 R11: 0000000000000246 R12: 00007f9a1d70c020 > > 869.881798] R13: 00007fffa5270030 R14: 00007fffa526fd00 R15: 0000000000000000 > > 863.881860] > > 863.881876) Modules linked in: snd_seq_dummy (E) snd_hrtimer (E)... > > ... > > 863.887142] button (E) > > 863.912127] CR2: ffffe4afcc079650 > > 863.914593] --- [ end trace 0000000000000000 1-- > > 864.042750] RIP: 0010:ctx_sched_out+0x1ce/0x210 > > 864.045214] Code: 89 c6 4c 8b b9 de 00 00 00 48 ... > > 864.050343] RSP: 0000:ffffaa4ec0f3fe60 EFLAGS: 00010086 > > 864.052929] RAX: 0000000000000002 RBX: ffff8e8eeed2a580 RCX: ffff8e8bded9bf00 > > 864.055518] RDX: 000000c92340b051 RSI: 000000c92340b051 RDI: ffff > > 864.058093] RBP: 0000000000000000 R08: 0000000000000002 R09: 00 > > 864.060654] R10: 0000000000000000 R11: 0000000000000000 R12: 000 > > 864.063183] R13: ffff8e8eeed2a580 R14: 0000000000000007 R15: ffffe4afcc079650 > > 864.065729] FS: 00007f9a1ca91940 (0000) GS:ffff8e8f6b1c3000(0000) knIGS:0000000000000000 > > 864.068312] CS: 0010 DS: 0000 ES: 0000 CRO: 0000000080050033 > > 864.070898] CR2: ffffe4afcc079650 CR3: 00000001136d8000 CR4: 0000000000350ef0 > > 864.673523] Kernel panic - not syncing: Fatal exception in interrupt > > 864.076410] Kernel Offset: 0xc00000 from 0xffffffff81000000 (relocation range: 0xff > > 864.205401] --- [ end Kernel panic - not syncing: Fatal exception in interrupt ]--- > > > > To address this call the perf_cgroup_event_disable() properly before > > list_del_event() in __perf_remove_from_context(). > > > > Link: https://lore.kernel.org/all/aD2TspKH%2F7yvfYoO@e129823.arm.com/ [0] > > Fixes: a3c3c6667("perf/core: Fix child_total_time_enabled accounting bug at task exit") > > Signed-off-by: Yeoreum Yun > > Tested-by: David Wang <00107082@163.com> > > --- > > kernel/events/core.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index f34c99f8ce8f..909b9d5a65c1 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -2498,6 +2498,10 @@ __perf_remove_from_context(struct perf_event *event, > > state = PERF_EVENT_STATE_DEAD; > > } > > event_sched_out(event, ctx); > > + > > + 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. Just for correct this, prior to commit a3c3c6667, Isn't the state change INACTIVE -> OFF -> EXIT? when I saw the perf_event_exit_event(), perf_remove_from_context(event, detacg_flags ... perf_event_set_state(event, PERF_EVENT_STATE_EXIT), So, 1. event_sched_out() -> INACTIVE 2. list_del_event() -> OFF 3. perf_event_set_state() -> EXIT. Therefore, the final event state is "PREF_EVENT_STATE_EXIT" Therefore, I think calling "perf_cgroup_event_disable()" is called as soon as event_sched_out() since commit a3c3c6667 change the state INCATIVE -> EXIT. so, the middle state of OFF is gone and I think this middle state "OFF" doesn't affect any race condition since the removed event "wakeup" is also called after it changed to "final state" -- in this case, the PERF_EVENT_STATE_EXIT. > > 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 > > 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); > > And we need to remove the perf_cgroup_event_disable() from > list_del_event() to avoid duplicate code. If we sustain perf_cgroup_event_disable()'s call in *list_del_event()* But, Should it be? I think its enough to call as soon as after event_sched_out(). > > Perhaps a better approach for code consolidation would be to modify > the conditions in list_del_event() to ensure the cgroup pointer is > cleaned up in error cases. However, I'm not confident that this is the > correct direction, so I would wait for suggestions from the maintainers. > > Thanks, > Leo [...] -- Sincerely, Yeoreum Yun