From: Athira Rajeev atrajeev@linux.vnet.ibm.com
commit f66de7ac4849eb42a7b18e26b8ee49e08130fd27 upstream.
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 bigeasy@linutronix.de Signed-off-by: Athira Rajeev atrajeev@linux.vnet.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/1606814880-1720-1-git-send-email-atrajeev@linux.vn... Signed-off-by: Hanjun Guo guohanjun@huawei.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 ded4a3e..9145231 100644 --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -1884,7 +1884,7 @@ 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]; @@ -1992,7 +1992,9 @@ 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)) { @@ -2003,13 +2005,13 @@ 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;