[tip:perfcounters/core] perf_counter: x86: Robustify interrupt handling

tip-bot for Peter Zijlstra
2009-05-15T08:47:09Z

Commit-ID: a4016a79fcbd139e7378944c0d86a39fdbc70ecc
Gitweb: http://git.kernel.org/tip/a4016a79fcbd139e7378944c0d86a39fdbc70ecc
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Thu, 14 May 2009 14:52:17 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 15 May 2009 09:47:03 +0200

perf_counter: x86: Robustify interrupt handling

Two consecutive NMIs could daze and confuse the machine when the
first would handle the overflow of both counters.

[ Impact: fix false-positive syslog messages under multi-session profiling ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
arch/x86/kernel/cpu/perf_counter.c | 16 +++++++++++++---
1 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 313638c..1dcf670 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -783,6 +783,10 @@ static int amd_pmu_handle_irq(struct pt_regs *regs, int nmi)

counter = cpuc->counters[idx];
hwc = &counter->hw;
+
+ if (counter->hw_event.nmi != nmi)
+ goto next;
+
val = x86_perf_counter_update(counter, hwc, idx);
if (val & (1ULL << (x86_pmu.counter_bits - 1)))
goto next;
@@ -869,7 +873,6 @@ perf_counter_nmi_handler(struct notifier_block *self,
{
struct die_args *args = __args;
struct pt_regs *regs;
- int ret;

if (!atomic_read(&active_counters))
return NOTIFY_DONE;
@@ -886,9 +889,16 @@ perf_counter_nmi_handler(struct notifier_block *self,
regs = args->regs;

apic_write(APIC_LVTPC, APIC_DM_NMI);
- ret = x86_pmu.handle_irq(regs, 1);
+ /*
+ * Can't rely on the handled return value to say it was our NMI, two
+ * counters could trigger 'simultaneously' raising two back-to-back NMIs.
+ *
+ * If the first NMI handles both, the latter will be empty and daze
+ * the CPU.
+ */
+ x86_pmu.handle_irq(regs, 1);

- return ret ? NOTIFY_STOP : NOTIFY_OK;
+ return NOTIFY_STOP;
}

static __read_mostly struct notifier_block perf_counter_nmi_notifier = {