Subject: perf,x86: Fix active_events imbalance
Commit 1b7b938f1817 ("perf/x86/intel: Fix PMI handling for Intel PT")
conditionally increments active_events in x86_add_exclusive() but
unconditionally decrements in x86_del_exclusive().
These extra decrements can lead to the situation where active_events is
zero and thus the PMI handler is 'disabled' while we have active events
on the PMU generating PMIs.
This leads to a truckload of:
Uhhuh. NMI received for unknown reason 21 on CPU 28.
Do you have a strange power saving mode enabled?
Dazed and confused, but trying to continue
messages and generally messes up perf.
Remove the condition on the increment, double increment balanced by a
double decrement is perfectly fine.
Restructure the code a little bit to make the unconditional inc a bit
more natural.
Fixes: 1b7b938f1817 ("perf/x86/intel: Fix PMI handling for Intel PT")
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/perf_event.c | 36 +++++++++++++-----------------------
1 file changed, 13 insertions(+), 23 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 5801a14..3658de4 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -357,34 +357,24 @@ void x86_release_hardware(void)
*/
int x86_add_exclusive(unsigned int what)
{
- int ret = -EBUSY, i;
-
- if (atomic_inc_not_zero(&x86_pmu.lbr_exclusive[what]))
- return 0;
+ int i;
- mutex_lock(&pmc_reserve_mutex);
- for (i = 0; i < ARRAY_SIZE(x86_pmu.lbr_exclusive); i++) {
- if (i != what && atomic_read(&x86_pmu.lbr_exclusive[i]))
- goto out;
+ if (!atomic_inc_not_zero(&x86_pmu.lbr_exclusive[what])) {
+ mutex_lock(&pmc_reserve_mutex);
+ for (i = 0; i < ARRAY_SIZE(x86_pmu.lbr_exclusive); i++) {
+ if (i != what && atomic_read(&x86_pmu.lbr_exclusive[i]))
+ goto fail_unlock;
+ }
+ atomic_inc(&x86_pmu.lbr_exclusive[what]);
+ mutex_unlock(&pmc_reserve_mutex);
}
- atomic_inc(&x86_pmu.lbr_exclusive[what]);
- ret = 0;
+ atomic_inc(&active_events);
+ return 0;
-out:
+fail_unlock:
mutex_unlock(&pmc_reserve_mutex);
-
- /*
- * Assuming that all exclusive events will share the PMI handler
- * (which checks active_events for whether there is work to do),
- * we can bump active_events counter right here, except for
- * x86_lbr_exclusive_lbr events that go through x86_pmu_event_init()
- * path, which already bumps active_events for them.
- */
- if (!ret && what != x86_lbr_exclusive_lbr)
- atomic_inc(&active_events);
-
- return ret;
+ return -EBUSY;
}
void x86_del_exclusive(unsigned int what)
--
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