Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754699Ab0KEVpq (ORCPT ); Fri, 5 Nov 2010 17:45:46 -0400 Received: from caiajhbdcahe.dreamhost.com ([208.97.132.74]:52946 "EHLO homiemail-a61.g.dreamhost.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752646Ab0KEVpp (ORCPT ); Fri, 5 Nov 2010 17:45:45 -0400 Subject: [PATCH] mce: fix RCU lockdep from mce_log() From: Davidlohr Bueso Reply-To: dave@gnu.org To: Andi Kleen , "Paul E. McKenney" Cc: LKML Content-Type: text/plain; charset="UTF-8" Date: Fri, 05 Nov 2010 18:44:59 -0300 Message-ID: <1288993499.2065.4.camel@cowboy> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4336 Lines: 115 Hi, Please review this patch, I am not very familiar with MCE/RCU so I'm not sure that this is the correct fix (otherwise consider it a bug report :)). This does "fix" the message though and I can use MCE normally. Thanks, Davidlohr From: Davidlohr Bueso Based on the following message: =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- arch/x86/kernel/cpu/mcheck/mce.c:1628 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 1 no locks held by mcelog/2350. stack backtrace: Pid: 2350, comm: mcelog Tainted: G W 2.6.37-rc1+ #7 Call Trace: [] lockdep_rcu_dereference+0xa4/0xc0 [] mce_poll+0xa9/0xd0 [] do_sys_poll+0x275/0x550 [] ? __pollwait+0x0/0xf0 [] ? pollwake+0x0/0x60 [] ? pollwake+0x0/0x60 [] ? rcu_read_lock_held+0x2c/0x30 [] ? radix_tree_lookup_element+0xda/0x100 [] ? __do_fault+0x128/0x470 [] ? filemap_fault+0xdb/0x4e0 [] ? unlock_page+0x25/0x30 [] ? sigprocmask+0x3f/0x100 [] ? _raw_spin_unlock_irq+0x2b/0x60 [] ? trace_hardirqs_on_caller+0x13d/0x180 [] ? trace_hardirqs_on+0xd/0x10 [] ? _raw_spin_unlock_irq+0x2b/0x60 [] sys_ppoll+0x47/0x190 [] ? trace_hardirqs_on_caller+0x13d/0x180 [] ? trace_hardirqs_on_thunk+0x3a/0x3f [] system_call_fastpath+0x16/0x1b At this point the arch/x86/kernel/cpu/mcheck/mce.c:1628 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 1 no locks held by mcelog/2350. stack backtrace: Pid: 2350, comm: mcelog Tainted: G W 2.6.37-rc1+ #7 Call Trace: [] lockdep_rcu_dereference+0xa4/0xc0 [] mce_poll+0xa9/0xd0 [] do_sys_poll+0x275/0x550 [] ? __pollwait+0x0/0xf0 [] ? pollwake+0x0/0x60 [] ? pollwake+0x0/0x60 [] ? rcu_read_lock_held+0x2c/0x30 [] ? radix_tree_lookup_element+0xda/0x100 [] ? __do_fault+0x128/0x470 [] ? filemap_fault+0xdb/0x4e0 [] ? unlock_page+0x25/0x30 [] ? sigprocmask+0x3f/0x100 [] ? _raw_spin_unlock_irq+0x2b/0x60 [] ? trace_hardirqs_on_caller+0x13d/0x180 [] ? trace_hardirqs_on+0xd/0x10 [] ? _raw_spin_unlock_irq+0x2b/0x60 [] sys_ppoll+0x47/0x190 [] ? trace_hardirqs_on_caller+0x13d/0x180 [] ? trace_hardirqs_on_thunk+0x3a/0x3f [] system_call_fastpath+0x16/0x1b At this point the lockdep_is_held(&mce_read_mutex) call is failing. So check if the mce_read_mutex is held before derefencing instead of using rcu_dereference_check_mce() Signed-off-by: Davidlohr Bueso --- arch/x86/kernel/cpu/mcheck/mce.c | 8 ++++++-- 1 files changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index 7a35b72..6f95b2c 100644 --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -1625,8 +1625,12 @@ out: static unsigned int mce_poll(struct file *file, poll_table *wait) { poll_wait(file, &mce_wait, wait); - if (rcu_dereference_check_mce(mcelog.next)) - return POLLIN | POLLRDNORM; + + if (mutex_is_locked(&mce_read_mutex)) { + if (rcu_dereference_index_check(mcelog.next, + rcu_read_lock_sched_held())) + return POLLIN | POLLRDNORM; + } if (!mce_apei_read_done && apei_check_mce()) return POLLIN | POLLRDNORM; return 0; -- 1.7.1 -- 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/