Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754809AbZFECgo (ORCPT ); Thu, 4 Jun 2009 22:36:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754548AbZFECgb (ORCPT ); Thu, 4 Jun 2009 22:36:31 -0400 Received: from bilbo.ozlabs.org ([203.10.76.25]:51201 "EHLO bilbo.ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753904AbZFECgb (ORCPT ); Thu, 4 Jun 2009 22:36:31 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <18984.33964.21541.743096@cargo.ozlabs.ibm.com> Date: Fri, 5 Jun 2009 12:36:28 +1000 From: Paul Mackerras To: Ingo Molnar Cc: Peter Zijlstra , linux-kernel@vger.kernel.org Subject: [PATCH] perf_counter: Fix lockup with interrupting counters X-Mailer: VM 8.0.12 under 22.2.1 (i486-pc-linux-gnu) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1548 Lines: 39 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 --- 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/