Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754158Ab0KHNRO (ORCPT ); Mon, 8 Nov 2010 08:17:14 -0500 Received: from e2.ny.us.ibm.com ([32.97.182.142]:47651 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753620Ab0KHNRN (ORCPT ); Mon, 8 Nov 2010 08:17:13 -0500 Date: Mon, 8 Nov 2010 05:17:08 -0800 From: "Paul E. McKenney" To: Davidlohr Bueso Cc: Andi Kleen , LKML Subject: Re: [PATCH] mce: fix RCU lockdep from mce_log() Message-ID: <20101108131708.GC2580@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1288993499.2065.4.camel@cowboy> <20101106185350.GA23824@basil.fritz.box> <20101107133950.GV15561@linux.vnet.ibm.com> <1289215819.2318.3.camel@cowboy> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1289215819.2318.3.camel@cowboy> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3655 Lines: 92 On Mon, Nov 08, 2010 at 08:30:19AM -0300, Davidlohr Bueso wrote: > 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? Looks good to me! Acked-by: Paul E. McKenney > 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/