From: Paul Mackerras Date: Fri, 5 Jun 2009 02:36:28 +0000 (+1000) Subject: perf_counter: Fix lockup with interrupting counters X-Git-Tag: v2.6.31-rc1~383^2~67 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=6dc5f2a41759987e35e757ef00192e7b424563bb 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 Cc: Peter Zijlstra LKML-Reference: <18984.33964.21541.743096@cargo.ozlabs.ibm.com> Signed-off-by: Ingo Molnar --- diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index 195712e20d07..a5d3e2aedd2f 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);