perf_counter: fix the output lock
Use -1 instead of 0 as unlocked, since 0 is a valid cpu number.
( This is not an issue right now but will be once we allow multiple
counters to output to the same mmap area. )
[ Impact: prepare code for multi-counter profile output ]
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: <20090505155437.232686598@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 2d13427..c881afe 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1409,6 +1409,7 @@
}
data->nr_pages = nr_pages;
+ atomic_set(&data->lock, -1);
rcu_assign_pointer(counter->data, data);
@@ -1755,7 +1756,7 @@
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 +1785,7 @@
* 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 +1795,7 @@
/*
* 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;