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Subject[tip:perfcounters/core] perf_counter: fix the output lock
Commit-ID:  22c1558e51c210787c6cf75d8905246fc91ec030
Gitweb: http://git.kernel.org/tip/22c1558e51c210787c6cf75d8905246fc91ec030
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Tue, 5 May 2009 17:50:25 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 5 May 2009 20:18:32 +0200

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>


---
kernel/perf_counter.c | 7 ++++---
1 files changed, 4 insertions(+), 3 deletions(-)
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 @@ static int perf_mmap_data_alloc(struct perf_counter *counter, int nr_pages)
}

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

rcu_assign_pointer(counter->data, data);

@@ -1755,7 +1756,7 @@ static void perf_output_lock(struct perf_output_handle *handle)
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 @@ 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 +1795,7 @@ 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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