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Subject[PATCH 5/7] perf_counter: fix the output lock
Use -1 instead of 0 as unlocked, since 0 is a valid cpu number.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
kernel/perf_counter.c | 39 ++++++++++++++++++++++++++++++++++-----
1 file changed, 34 insertions(+), 5 deletions(-)
Index: linux-2.6/kernel/perf_counter.c
===================================================================
--- linux-2.6.orig/kernel/perf_counter.c
+++ linux-2.6/kernel/perf_counter.c
@@ -1409,6 +1417,7 @@ static int perf_mmap_data_alloc(struct p
}

data->nr_pages = nr_pages;
+ atomic_set(&data->lock, -1);

rcu_assign_pointer(counter->data, data);

@@ -1755,7 +1764,7 @@ static void perf_output_lock(struct perf
if (in_nmi() && atomic_read(&data->lock) == cpu)
return;

- while (atomic_cmpxchg(&data->lock, 0, cpu) != 0)
+ while (atomic_cmpxchg(&data->lock, -1, cpu) != -1)
cpu_relax();

handle->locked = 1;
@@ -1784,7 +1793,7 @@ again:
* NMI can happen here, which means we can miss a done_head update.
*/

- cpu = atomic_xchg(&data->lock, 0);
+ cpu = atomic_xchg(&data->lock, -1);
WARN_ON_ONCE(cpu != smp_processor_id());

/*
@@ -1794,7 +1803,7 @@ again:
/*
* Since we had it locked, we can lock it again.
*/
- while (atomic_cmpxchg(&data->lock, 0, cpu) != 0)
+ while (atomic_cmpxchg(&data->lock, -1, cpu) != -1)
cpu_relax();

goto again;
--



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