From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Triplett Subject: Re: [PATCH v2 tip/core/rcu 05/13] decnet: Apply rcu_access_pointer() to avoid sparse false positive Date: Wed, 9 Oct 2013 15:28:42 -0700 Message-ID: <20131009222842.GD11709@jtriplet-mobl1> References: <20131009212920.GA15413@linux.vnet.ibm.com> <1381354186-16285-1-git-send-email-paulmck@linux.vnet.ibm.com> <1381354186-16285-5-git-send-email-paulmck@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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, 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, "David S. Miller" , Thomas Graf , Gao feng , Stephen Hemminger , linux-decnet-user@lists.sourceforge.net, netdev@vger.kernel.org To: "Paul E. McKenney" Return-path: Content-Disposition: inline In-Reply-To: <1381354186-16285-5-git-send-email-paulmck@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, Oct 09, 2013 at 02:29:38PM -0700, Paul E. McKenney wrote: > 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 use in > dn_insert_route() is legitimate: It is assigning a pointer to an element Nit: "uses ... are", not "use ... is". :) > from an RCU-protected list, and all elements of this list are already > visible to caller. > > This commit therefore silences this false positive by laundering the > pointer using rcu_access_pointer() as suggested by Josh Triplett. > > Reported-by: kbuild test robot > Signed-off-by: Paul E. McKenney > Cc: "David S. Miller" > Cc: Thomas Graf > Cc: Gao feng > Cc: Stephen Hemminger > Cc: linux-decnet-user@lists.sourceforge.net > Cc: netdev@vger.kernel.org With or without the above typo fix: Reviewed-by: Josh Triplett > --- > net/decnet/dn_route.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c > index fe32388ea24f..3b1357bcfc92 100644 > --- a/net/decnet/dn_route.c > +++ b/net/decnet/dn_route.c > @@ -345,7 +345,7 @@ static int dn_insert_route(struct dn_route *rt, unsigned int hash, struct dn_rou > /* Put it first */ > *rthp = rth->dst.dn_next; > rcu_assign_pointer(rth->dst.dn_next, > - dn_rt_hash_table[hash].chain); > + rcu_access_pointer(dn_rt_hash_table[hash].chain)); > rcu_assign_pointer(dn_rt_hash_table[hash].chain, rth); > > dst_use(&rth->dst, now); > @@ -358,7 +358,8 @@ static int dn_insert_route(struct dn_route *rt, unsigned int hash, struct dn_rou > rthp = &rth->dst.dn_next; > } > > - rcu_assign_pointer(rt->dst.dn_next, dn_rt_hash_table[hash].chain); > + rcu_assign_pointer(rt->dst.dn_next, > + rcu_access_pointer(dn_rt_hash_table[hash].chain)); > rcu_assign_pointer(dn_rt_hash_table[hash].chain, rt); > > dst_use(&rt->dst, now); > -- > 1.8.1.5 >