Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754584Ab0KHLaw (ORCPT ); Mon, 8 Nov 2010 06:30:52 -0500 Received: from caiajhbdcbef.dreamhost.com ([208.97.132.145]:39805 "EHLO homiemail-a2.g.dreamhost.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754422Ab0KHLau convert rfc822-to-8bit (ORCPT ); Mon, 8 Nov 2010 06:30:50 -0500 Subject: Re: [PATCH] mce: fix RCU lockdep from mce_log() From: Davidlohr Bueso Reply-To: dave@gnu.org To: paulmck@linux.vnet.ibm.com Cc: Andi Kleen , LKML In-Reply-To: <20101107133950.GV15561@linux.vnet.ibm.com> References: <1288993499.2065.4.camel@cowboy> <20101106185350.GA23824@basil.fritz.box> <20101107133950.GV15561@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 08 Nov 2010 08:30:19 -0300 Message-ID: <1289215819.2318.3.camel@cowboy> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3352 Lines: 87 On Sun, 2010-11-07 at 05:39 -0800, Paul E. McKenney wrote: > On Sat, Nov 06, 2010 at 07:53:50PM +0100, Andi Kleen wrote: > > On Fri, Nov 05, 2010 at 06:44:59PM -0300, Davidlohr Bueso wrote: > > > 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. > > > > The patch is certainly not correct. The variable needs to be read > > independently of the mutex. > > This code is simply checking the value of the pointer, and therefore > need not protect any actual dereferences. So why not replace the > rcu_dereference_check_mce() with rcu_access_pointer()? If this is > OK, please see the patch below. > > BTW, assigning the value returned by rcu_access_pointer() into a > variable often indicates a bug. ;-) > > Thanx, Paul > > Signed-off-by: Paul E. McKenney > > diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c > index 7a35b72..4d29d50 100644 > --- a/arch/x86/kernel/cpu/mcheck/mce.c > +++ b/arch/x86/kernel/cpu/mcheck/mce.c > @@ -1625,7 +1625,7 @@ 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)) > + if (rcu_access_pointer(mcelog.next)) this doesn't compile (mcelog.next is an index): arch/x86/kernel/cpu/mcheck/mce.c: In function ‘mce_poll’: arch/x86/kernel/cpu/mcheck/mce.c:1628: error: invalid type argument of ‘unary *’ (have ‘unsigned int’) arch/x86/kernel/cpu/mcheck/mce.c:1628: warning: type defaults to ‘int’ in declaration of ‘_________p1’ arch/x86/kernel/cpu/mcheck/mce.c:1628: error: invalid type argument of ‘unary *’ (have ‘unsigned int’) arch/x86/kernel/cpu/mcheck/mce.c:1628: warning: type defaults to ‘int’ in declaration of ‘type name’ arch/x86/kernel/cpu/mcheck/mce.c:1628: warning: cast to pointer from integer of different size arch/x86/kernel/cpu/mcheck/mce.c:1628: error: invalid type argument of ‘unary *’ (have ‘unsigned int’) arch/x86/kernel/cpu/mcheck/mce.c:1628: warning: type defaults to ‘int’ in declaration of ‘type name’ make[4]: *** [arch/x86/kernel/cpu/mcheck/mce.o] Error 1 Since the mutex is independent, what about this patch? Signed-off-by: Davidlohr Bueso --- arch/x86/kernel/cpu/mcheck/mce.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index 7a35b72..cc1c673 100644 --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -1625,7 +1625,7 @@ 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)) + 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; -- 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/