linux-kernel - [PATCH] perf: fix alloc_callchain

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Date:	Tue, 25 Jan 2011 19:40:51 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>, stable@...nel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	David Miller <davem@...emloft.net>,
	Stephane Eranian <eranian@...gle.com>
Subject: [PATCH] perf: fix alloc_callchain_buffers()

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@...il.com>
CC: Frederic Weisbecker <fweisbec@...il.com>
CC: Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC: Arnaldo Carvalho de Melo <acme@...hat.com>
CC: David Miller <davem@...emloft.net>
CC: Stephane Eranian <eranian@...gle.com>
CC: stable@...nel.org
---
 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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