diff options
authorJiri Olsa <jolsa@kernel.org>2019-05-04 17:15:56 +0200
committerIngo Molnar <mingo@kernel.org>2019-05-05 13:00:48 +0200
commit6f55967ad9d9752813e36de6d5fdbd19741adfc7 (patch)
parent72e830f68428ab9ea9eca65d160795f4e02cecfc (diff)
perf/x86/intel: Fix race in intel_pmu_disable_event()
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>
1 files changed, 7 insertions, 3 deletions
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index f9451566cd9b..d35f4775d5f1 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2091,15 +2091,19 @@ 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)) {
+ /*
+ * 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)