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authorPaul Mackerras <paulus@samba.org>2009-06-05 12:36:28 +1000
committerIngo Molnar <mingo@elte.hu>2009-06-05 08:22:26 +0200
commit6dc5f2a41759987e35e757ef00192e7b424563bb (patch)
treeb7dddd415cd2d4dcf4e060a8fc769903d2a57a01
parent76a0f40fd6eff1bce3b91925cea7587b3399fe80 (diff)
perf_counter: Fix lockup with interrupting counters
Commit 8e3747c1 ("perf_counter: Change data head from u32 to u64") changed the type of 'head' in struct perf_mmap_data from atomic_t to atomic_long_t, but missed converting one use of atomic_read on it to atomic_long_read. The effect of using atomic_read rather than atomic_long_read on powerpc (and other big-endian architectures) is that we get the high half of the 64-bit quantity, resulting in the cmpxchg retry loop in perf_output_begin spinning forever as soon as data->head becomes non-zero. On little-endian architectures such as x86 we would get the low half, resulting in a lockup once data->head becomes greater than 4G. This fixes it by using atomic_long_read rather than atomic_read. [ Impact: fix perfcounter lockup on PowerPC / big-endian systems ] Signed-off-by: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <18984.33964.21541.743096@cargo.ozlabs.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/perf_counter.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 195712e20d0..a5d3e2aedd2 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -2234,7 +2234,7 @@ static int perf_output_begin(struct perf_output_handle *handle,
perf_output_lock(handle);
do {
- offset = head = atomic_read(&data->head);
+ offset = head = atomic_long_read(&data->head);
head += size;
} while (atomic_long_cmpxchg(&data->head, offset, head) != offset);