diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2013-10-28 13:55:29 +0100 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2013-11-28 14:01:59 +0000 |
| commit | d08b0a5594dde8b0fbda5d38cb01a81954a9829e (patch) | |
| tree | 8139b8fc0fbf21b7a0feb3880fe4722cd6dee415 /include | |
| parent | 498a727b33ee121e4b57428257a05f657674af46 (diff) | |
perf: Fix perf ring buffer memory ordering
commit bf378d341e4873ed928dc3c636252e6895a21f50 upstream.
The PPC64 people noticed a missing memory barrier and crufty old
comments in the perf ring buffer code. So update all the comments and
add the missing barrier.
When the architecture implements local_t using atomic_long_t there
will be double barriers issued; but short of introducing more
conditional barrier primitives this is the best we can do.
Reported-by: Victor Kaplansky <victork@il.ibm.com>
Tested-by: Victor Kaplansky <victork@il.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: michael@ellerman.id.au
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: anton@samba.org
Cc: benh@kernel.crashing.org
Link: http://lkml.kernel.org/r/20131025173749.GG19466@laptop.lan
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/perf_event.h | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index eeb6a29ee1e1..8d5b91ec2b19 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -300,13 +300,15 @@ struct perf_event_mmap_page { /* * Control data for the mmap() data buffer. * - * User-space reading the @data_head value should issue an rmb(), on - * SMP capable platforms, after reading this value -- see - * perf_event_wakeup(). + * User-space reading the @data_head value should issue an smp_rmb(), + * after reading this value. * * When the mapping is PROT_WRITE the @data_tail value should be - * written by userspace to reflect the last read data. In this case - * the kernel will not over-write unread data. + * written by userspace to reflect the last read data, after issueing + * an smp_mb() to separate the data read from the ->data_tail store. + * In this case the kernel will not over-write unread data. + * + * See perf_output_put_handle() for the data ordering. */ __u64 data_head; /* head in the data section */ __u64 data_tail; /* user-space written tail */ |