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>

1 files changed, 14 insertions, 5 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index ab4455447f84..0bb03f15a5b6 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;
                 }
         }