Consider the following scenario, While scheduling out an IBS event from perf's core scheduling path, event_sched_out() disables the IBS event by clearing the IBS enable bit in perf_ibs_disable_event(). However, if a delayed IBS NMI is delivered after the IBS enable bit is cleared, the IBS NMI handler may still observe the valid bit set and incorrectly treat the sample as valid. As a result, it re-enables IBS by setting the enable bit, even though the event has already been scheduled out. This leads to a situation where IBS is re-enabled after being explicitly disabled, which is incorrect. Although this race does not have visible side effects, it violates the expected behavior of the perf subsystem. The race is particularly noticeable when userspace repeatedly disables and re-enables IBS using PERF_EVENT_IOC_DISABLE and PERF_EVENT_IOC_ENABLE ioctls in a loop. Fix this by checking the IBS_STOPPED bit in the IBS NMI handler before re-enabling the IBS event. If the IBS_STOPPED bit is set, it indicates that the event is either disabled or in the process of being disabled, and the NMI handler should not re-enable it. Signed-off-by: Manali Shukla <manali.shukla@xxxxxxx> --- arch/x86/events/amd/ibs.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c index 0252b7ea8bca..c998f68eeddc 100644 --- a/arch/x86/events/amd/ibs.c +++ b/arch/x86/events/amd/ibs.c @@ -1386,7 +1386,8 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs) } new_config |= period >> 4; - perf_ibs_enable_event(perf_ibs, hwc, new_config); + if (!test_bit(IBS_STOPPING, pcpu->state)) + perf_ibs_enable_event(perf_ibs, hwc, new_config); } perf_event_update_userpage(event); base-commit: 61374cc145f4a56377eaf87c7409a97ec7a34041 prerequisite-patch-id: 0094bc7b958de1caba7b779c1c2dc96b3e1bcac1 prerequisite-patch-id: 58a6a462207dd7ec06998d6ff6a418f373f25d43 prerequisite-patch-id: 42d94622dfc4ccc786ce9bd6be186dbc5d32ed5b prerequisite-patch-id: d93658ba28ece72eb6b9e2bb2a2a6188c4654216 prerequisite-patch-id: 669a4b410b39f4f34b9bcc4748a277ad2ac3b24c 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