From c33a0bc4e41ef169d6e807d8abb9502544b518e5 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 1 May 2009 12:23:16 +0200 Subject: perf_counter: fix race in perf_output_* When two (or more) contexts output to the same buffer, it is possible to observe half written output. Suppose we have CPU0 doing perf_counter_mmap(), CPU1 doing perf_counter_overflow(). If CPU1 does a wakeup and exposes head to user-space, then CPU2 can observe the data CPU0 is still writing. [ Impact: fix occasionally corrupted profiling records ] Signed-off-by: Peter Zijlstra Cc: Paul Mackerras Cc: Corey Ashford LKML-Reference: <20090501102533.007821627@chello.nl> Signed-off-by: Ingo Molnar --- include/linux/perf_counter.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h index 41aed427005..f776851f8c4 100644 --- a/include/linux/perf_counter.h +++ b/include/linux/perf_counter.h @@ -358,10 +358,13 @@ struct perf_mmap_data { struct rcu_head rcu_head; int nr_pages; /* nr of data pages */ - atomic_t wakeup; /* POLL_ for wakeups */ + atomic_t poll; /* POLL_ for wakeups */ atomic_t head; /* write position */ atomic_t events; /* event limit */ + atomic_t wakeup_head; /* completed head */ + atomic_t lock; /* concurrent writes */ + struct perf_counter_mmap_page *user_page; void *data_pages[0]; }; -- cgit v1.2.3