From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ding Tianhong Subject: Re: [PATCH tip/core/rcu 11/14] bonding/bond_main: Apply ACCESS_ONCE() to avoid sparse false positive Date: Sat, 16 Nov 2013 12:32:16 +0800 Message-ID: <5286F550.10900@gmail.com> References: <20131116003946.GA316@linux.vnet.ibm.com> <1384562417-817-1-git-send-email-paulmck@linux.vnet.ibm.com> <1384562417-817-11-git-send-email-paulmck@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, Stephen Hemminger , "David S. Miller" , bridge@lists.linux-foundation.org, netdev@vger.kernel.org To: "Paul E. McKenney" Return-path: In-Reply-To: <1384562417-817-11-git-send-email-paulmck@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org =D3=DA 2013/11/16 8:40, Paul E. McKenney =D0=B4=B5=C0: > From: "Paul E. McKenney" > > The sparse checking for rcu_assign_pointer() was recently upgraded > to reject non-__kernel address spaces. This also rejects __rcu, > which is almost always the right thing to do. However, the uses in > bond_change_active_slave() and __bond_release_one() are legitimate: > They are assigning a pointer to an element from an RCU-protected list > (or a NULL pointer), and all elements of this list are already visibl= e > to caller. > > This commit therefore silences these false positives either by launde= ring > the pointers using ACCESS_ONCE() as suggested by Eric Dumazet and Jos= h > Triplett, or by using RCU_INIT_POINTER() for NULL pointer assignments= =2E I think it is fit for net-next. > Reported-by: kbuild test robot > Signed-off-by: Paul E. McKenney > Cc: Stephen Hemminger > Cc: "David S. Miller" > Cc: bridge@lists.linux-foundation.org > Cc: netdev@vger.kernel.org > --- > drivers/net/bonding/bond_main.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bo= nd_main.c > index 72df399c4ab3..bbd7fd3e46fe 100644 > --- a/drivers/net/bonding/bond_main.c > +++ b/drivers/net/bonding/bond_main.c > @@ -890,7 +890,8 @@ void bond_change_active_slave(struct bonding *bon= d, struct slave *new_active) > if (new_active) > bond_set_slave_active_flags(new_active); > } else { > - rcu_assign_pointer(bond->curr_active_slave, new_active); > + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ > + ACCESS_ONCE(bond->curr_active_slave) =3D new_active; > } > =20 > if (bond->params.mode =3D=3D BOND_MODE_ACTIVEBACKUP) { > @@ -1801,7 +1802,7 @@ static int __bond_release_one(struct net_device= *bond_dev, > } > =20 > if (all) { > - rcu_assign_pointer(bond->curr_active_slave, NULL); > + RCU_INIT_POINTER(bond->curr_active_slave, NULL); > } else if (oldcurrent =3D=3D slave) { > /* > * Note that we hold RTNL over this sequence, so there