From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752430Ab1ARRsl (ORCPT ); Tue, 18 Jan 2011 12:48:41 -0500 Received: from e3.ny.us.ibm.com ([32.97.182.143]:47026 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751122Ab1ARRsj (ORCPT ); Tue, 18 Jan 2011 12:48:39 -0500 Date: Tue, 18 Jan 2011 09:48:34 -0800 From: "Paul E. McKenney" To: "Michael S. Tsirkin" Cc: Jason Wang , kvm@vger.kernel.org, virtualization@lists.osdl.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] vhost: rcu annotation fixup Message-ID: <20110118174834.GF2193@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110118110845.GA11555@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110118110845.GA11555@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) X-Content-Scanned: Fidelis XPS MAILER Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 18, 2011 at 01:08:45PM +0200, Michael S. Tsirkin wrote: > When built with rcu checks enabled, vhost triggers > bogus warnings as vhost features are read without > dev->mutex sometimes. > Fixing it properly is not trivial as vhost.h does not > know which lockdep classes it will be used under. > Disable the warning by stubbing out the check for now. > > Signed-off-by: Michael S. Tsirkin > --- > drivers/vhost/vhost.h | 4 +--- > 1 files changed, 1 insertions(+), 3 deletions(-) > > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > index 2af44b7..2d03a31 100644 > --- a/drivers/vhost/vhost.h > +++ b/drivers/vhost/vhost.h > @@ -173,9 +173,7 @@ static inline int vhost_has_feature(struct vhost_dev *dev, int bit) > { > unsigned acked_features; > > - acked_features = > - rcu_dereference_index_check(dev->acked_features, > - lockdep_is_held(&dev->mutex)); > + acked_features = rcu_dereference_index_check(dev->acked_features, 1); Ouch!!! Could you please at least add a comment? Alternatively, pass in the lock that is held and check for that? Given that this is a static inline, the compiler should be able to optimize the argument away when !PROVE_RCU, correct? Thanx, Paul > return acked_features & (1 << bit); > } > > -- > 1.7.3.2.91.g446ac > -- > 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/