The power_pmu_event_init() callback access per-cpu variable
(cpu_hw_events) to check for event constraints and Branch Stack
(BHRB). Current usage is to disable preemption when accessing the
per-cpu variable, but this does not prevent timer callback from
interrupting event_init. Fix this by using 'local_irq_save/restore'
to make sure the code path is invoked with disabled interrupts.
This change is tested in mambo simulator to ensure that, if a timer
interrupt comes in during the per-cpu access in event_init, it will be
soft masked and replayed later. For testing purpose, introduced a
udelay() in power_pmu_event_init() to make sure a timer interrupt arrives
while in per-cpu variable access code between local_irq_save/resore.
As expected the timer interrupt was replayed later during local_irq_restore
called from power_pmu_event_init. This was confirmed by adding
breakpoint in mambo and checking the backtrace when timer_interrupt
was hit.
Reported-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
Signed-off-by: Athira Rajeev <atraj...@linux.vnet.ibm.com>
---
arch/powerpc/perf/core-book3s.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 3c8c6ce..e38648f0 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1909,7 +1909,7 @@ static bool is_event_blacklisted(u64 ev)
static int power_pmu_event_init(struct perf_event *event)
{
u64 ev;
- unsigned long flags;
+ unsigned long flags, irq_flags;
struct perf_event *ctrs[MAX_HWEVENTS];
u64 events[MAX_HWEVENTS];
unsigned int cflags[MAX_HWEVENTS];
@@ -2017,7 +2017,9 @@ static int power_pmu_event_init(struct perf_event *event)
if (check_excludes(ctrs, cflags, n, 1))
return -EINVAL;
- cpuhw = &get_cpu_var(cpu_hw_events);
+ local_irq_save(irq_flags);
+ cpuhw = this_cpu_ptr(&cpu_hw_events);
+
err = power_check_constraints(cpuhw, events, cflags, n + 1);
if (has_branch_stack(event)) {
@@ -2028,13 +2030,13 @@ static int power_pmu_event_init(struct perf_event
*event)
event->attr.branch_sample_type);
if (bhrb_filter == -1) {
- put_cpu_var(cpu_hw_events);
+ local_irq_restore(irq_flags);
return -EOPNOTSUPP;
}
cpuhw->bhrb_filter = bhrb_filter;
}
- put_cpu_var(cpu_hw_events);
+ local_irq_restore(irq_flags);
if (err)
return -EINVAL;
--
1.8.3.1
