From mboxrd@z Thu Jan 1 00:00:00 1970 From: mengcong Subject: [PATCH] VFS: br_write_lock locks on possible CPUs other than online CPUs Date: Mon, 19 Dec 2011 11:36:15 +0800 Message-ID: <1324265775.25089.20.camel@mengcong> Reply-To: mc@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Nick Piggin To: Alexander Viro Return-path: Received: from e28smtp05.in.ibm.com ([122.248.162.5]:54455 "EHLO e28smtp05.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752132Ab1LSDgZ (ORCPT ); Sun, 18 Dec 2011 22:36:25 -0500 Received: from /spool/local by e28smtp05.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 19 Dec 2011 09:06:23 +0530 Sender: linux-fsdevel-owner@vger.kernel.org List-ID: In a heavily loaded system, when frequently turning on and off CPUs, the kernel will detect soft-lockups on multiple CPUs. The detailed bug report is at https://lkml.org/lkml/2011/8/24/185. The root cause is that brlock functions, i.e. br_write_lock() and br_write_unlock(), only locks/unlocks the per-CPU spinlock of CPUs that are online, which means, if one online CPU is locked and then goes offline, any later unlocking operation happens during its offline state will not touch it; and when it goes online again, it has the incorrect brlock state. This has been verified in current kernel. I can reproduce this bug on the intact 3.1 kernel. After my patch applied, I've ran an 8-hours long test(test script provided by the bug reporter), and no soft lockup happened again. Signed-off-by: Cong Meng Reported-by: Srivatsa S. Bhat --- include/linux/lglock.h | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/lglock.h b/include/linux/lglock.h index f549056..08b9e84 100644 --- a/include/linux/lglock.h +++ b/include/linux/lglock.h @@ -27,8 +27,8 @@ #define br_lock_init(name) name##_lock_init() #define br_read_lock(name) name##_local_lock() #define br_read_unlock(name) name##_local_unlock() -#define br_write_lock(name) name##_global_lock_online() -#define br_write_unlock(name) name##_global_unlock_online() +#define br_write_lock(name) name##_global_lock() +#define br_write_unlock(name) name##_global_unlock() #define DECLARE_BRLOCK(name) DECLARE_LGLOCK(name) #define DEFINE_BRLOCK(name) DEFINE_LGLOCK(name) -- 1.7.5.4