[PATCH] perf: fix alloc_callchain_buffers()

From: Eric Dumazet
Date: Tue Jan 25 2011 - 13:41:01 EST

Commit 927c7a9e92c4 ( perf: Fix race in callchains ) introduced a
mismatch in the sizing of struct callchain_cpus_entries.

nr_cpu_ids must be used instead of num_possible_cpus(), or we might get
out of bound memory accesses on some machines.

Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
CC: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CC: David Miller <davem@xxxxxxxxxxxxx>
CC: Stephane Eranian <eranian@xxxxxxxxxx>
CC: stable@xxxxxxxxxx
kernel/perf_event.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 126a302..852ae8c 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1999,8 +1999,7 @@ static int alloc_callchain_buffers(void)
* accessed from NMI. Use a temporary manual per cpu allocation
* until that gets sorted out.
- size = sizeof(*entries) + sizeof(struct perf_callchain_entry *) *
- num_possible_cpus();
+ size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);

entries = kzalloc(size, GFP_KERNEL);
if (!entries)

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