[tip:perfcounters/core] perf_counter: Fix throttling lock-up

tip-bot for Ingo Molnar
2009-06-03T21:43:51Z

Commit-ID: 128f048f0f0d2a477ad2555e7acd2ad15a1b6061
Gitweb: http://git.kernel.org/tip/128f048f0f0d2a477ad2555e7acd2ad15a1b6061
Author: Ingo Molnar <mingo@elte.hu>
AuthorDate: Wed, 3 Jun 2009 22:19:36 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 3 Jun 2009 23:39:51 +0200

perf_counter: Fix throttling lock-up

Throttling logic is broken and we can lock up with too small
hw sampling intervals.

Make the throttling code more robust: disable counters even
if we already disabled them.

( Also clean up whitespace damage i noticed while reading
various pieces of code related to throttling. )

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
arch/x86/kernel/cpu/perf_counter.c | 2 +-
kernel/perf_counter.c | 19 ++++++++++++++-----
2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 12cc05e..8f53f3a 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -91,7 +91,7 @@ static u64 intel_pmu_raw_event(u64 event)
#define CORE_EVNTSEL_INV_MASK 0x00800000ULL
#define CORE_EVNTSEL_COUNTER_MASK 0xFF000000ULL

-#define CORE_EVNTSEL_MASK \
+#define CORE_EVNTSEL_MASK \
(CORE_EVNTSEL_EVENT_MASK | \
CORE_EVNTSEL_UNIT_MASK | \
CORE_EVNTSEL_EDGE_MASK | \
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index ab44554..0bb03f1 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -2822,11 +2822,20 @@ int perf_counter_overflow(struct perf_counter *counter,

if (!throttle) {
counter->hw.interrupts++;
- } else if (counter->hw.interrupts != MAX_INTERRUPTS) {
- counter->hw.interrupts++;
- if (HZ*counter->hw.interrupts > (u64)sysctl_perf_counter_limit) {
- counter->hw.interrupts = MAX_INTERRUPTS;
- perf_log_throttle(counter, 0);
+ } else {
+ if (counter->hw.interrupts != MAX_INTERRUPTS) {
+ counter->hw.interrupts++;
+ if (HZ*counter->hw.interrupts > (u64)sysctl_perf_counter_limit) {
+ counter->hw.interrupts = MAX_INTERRUPTS;
+ perf_log_throttle(counter, 0);
+ ret = 1;
+ }
+ } else {
+ /*
+ * Keep re-disabling counters even though on the previous
+ * pass we disabled it - just in case we raced with a
+ * sched-in and the counter got enabled again:
+ */
ret = 1;
}
}