[PATCH 2/2] perf_counter: Fix an ipi-deadlock

From: Peter Zijlstra
Date: Wed Aug 12 2009 - 11:43:03 EST


perf_pending_counter() is called from IRQ context and will call
perf_counter_disable(), however perf_counter_disable() uses
smp_call_function_single() which doesn't fancy being used with IRQs
disabled due to IPI deadlocks.

Fix this by making it use the local __perf_counter_disable() call and
teaching the counter_sched_out() code about pending disables as well.

This should cover the case where a counter migrates before the pending
queue gets processed.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
kernel/perf_counter.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

Index: linux-2.6/kernel/perf_counter.c
===================================================================
--- linux-2.6.orig/kernel/perf_counter.c
+++ linux-2.6/kernel/perf_counter.c
@@ -307,6 +307,10 @@ counter_sched_out(struct perf_counter *c
return;

counter->state = PERF_COUNTER_STATE_INACTIVE;
+ if (counter->pending_disable) {
+ counter->pending_disable = 0;
+ counter->state = PERF_COUNTER_STATE_OFF;
+ }
counter->tstamp_stopped = ctx->time;
counter->pmu->disable(counter);
counter->oncpu = -1;
@@ -2315,7 +2319,7 @@ static void perf_pending_counter(struct

if (counter->pending_disable) {
counter->pending_disable = 0;
- perf_counter_disable(counter);
+ __perf_counter_disable(counter);
}

if (counter->pending_wakeup) {

--

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