[ Upstream commit 6f55967ad9d9752813e36de6d5fdbd19741adfc7 ]
New race in x86_pmu_stop() was introduced by replacing the atomic __test_and_clear_bit() of cpuc->active_mask by separate test_bit() and __clear_bit() calls in the following commit:
3966c3feca3f ("x86/perf/amd: Remove need to check "running" bit in NMI handler")
The race causes panic for PEBS events with enabled callchains:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 ... RIP: 0010:perf_prepare_sample+0x8c/0x530 Call Trace: <NMI> perf_event_output_forward+0x2a/0x80 __perf_event_overflow+0x51/0xe0 handle_pmi_common+0x19e/0x240 intel_pmu_handle_irq+0xad/0x170 perf_event_nmi_handler+0x2e/0x50 nmi_handle+0x69/0x110 default_do_nmi+0x3e/0x100 do_nmi+0x11a/0x180 end_repeat_nmi+0x16/0x1a RIP: 0010:native_write_msr+0x6/0x20 ... </NMI> intel_pmu_disable_event+0x98/0xf0 x86_pmu_stop+0x6e/0xb0 x86_pmu_del+0x46/0x140 event_sched_out.isra.97+0x7e/0x160 ...
The event is configured to make samples from PEBS drain code, but when it's disabled, we'll go through NMI path instead, where data->callchain will not get allocated and we'll crash:
x86_pmu_stop test_bit(hwc->idx, cpuc->active_mask) intel_pmu_disable_event(event) { ... intel_pmu_pebs_disable(event); ...
EVENT OVERFLOW -> <NMI> intel_pmu_handle_irq handle_pmi_common TEST PASSES -> test_bit(bit, cpuc->active_mask)) perf_event_overflow perf_prepare_sample { ... if (!(sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY)) data->callchain = perf_callchain(event, regs);
CRASH -> size += data->callchain->nr; } </NMI> ... x86_pmu_disable_event(event) }
__clear_bit(hwc->idx, cpuc->active_mask);
Fixing this by disabling the event itself before setting off the PEBS bit.
Signed-off-by: Jiri Olsa jolsa@kernel.org Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Arnaldo Carvalho de Melo acme@redhat.com Cc: David Arcari darcari@redhat.com Cc: Jiri Olsa jolsa@redhat.com Cc: Lendacky Thomas Thomas.Lendacky@amd.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Stephane Eranian eranian@google.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Vince Weaver vincent.weaver@maine.edu Fixes: 3966c3feca3f ("x86/perf/amd: Remove need to check "running" bit in NMI handler") Link: http://lkml.kernel.org/r/20190504151556.31031-1-jolsa@kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/events/intel/core.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c index a759e59990fbd..09c53bcbd497d 100644 --- a/arch/x86/events/intel/core.c +++ b/arch/x86/events/intel/core.c @@ -2074,15 +2074,19 @@ static void intel_pmu_disable_event(struct perf_event *event) cpuc->intel_ctrl_host_mask &= ~(1ull << hwc->idx); cpuc->intel_cp_status &= ~(1ull << hwc->idx);
- if (unlikely(event->attr.precise_ip)) - intel_pmu_pebs_disable(event); - if (unlikely(hwc->config_base == MSR_ARCH_PERFMON_FIXED_CTR_CTRL)) { intel_pmu_disable_fixed(hwc); return; }
x86_pmu_disable_event(event); + + /* + * Needs to be called after x86_pmu_disable_event, + * so we don't trigger the event without PEBS bit set. + */ + if (unlikely(event->attr.precise_ip)) + intel_pmu_pebs_disable(event); }
static void intel_pmu_del_event(struct perf_event *event)