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Date: Fri, 5 Jun 2009 12:36:28 +1000 From: Paul Mackerras <paulus@...ba.org> To: Ingo Molnar <mingo@...e.hu> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-kernel@...r.kernel.org Subject: [PATCH] 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. Signed-off-by: Paul Mackerras <paulus@...ba.org> --- kernel/perf_counter.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index 195712e..a5d3e2a 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); -- 1.6.0.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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