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Message-ID: <YEcukkO7bsKYVqEZ@shredder.lan>
Date: Tue, 9 Mar 2021 10:15:14 +0200
From: Ido Schimmel <idosch@...sch.org>
To: David Ahern <dsahern@...il.com>
Cc: Wei Wang <weiwan@...gle.com>,
"David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
Ido Schimmel <idosch@...dia.com>,
Petr Machata <petrm@...dia.com>,
syzbot <syzkaller@...glegroups.com>,
David Ahern <dsahern@...nel.org>,
Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] ipv6: fix suspecious RCU usage warning
On Mon, Mar 08, 2021 at 07:47:31PM -0700, David Ahern wrote:
> [ cc Ido and Petr ]
>
> On 3/8/21 12:21 PM, Wei Wang wrote:
> > diff --git a/include/net/nexthop.h b/include/net/nexthop.h
> > index 7bc057aee40b..48956b144689 100644
> > --- a/include/net/nexthop.h
> > +++ b/include/net/nexthop.h
> > @@ -410,31 +410,39 @@ static inline struct fib_nh *fib_info_nh(struct fib_info *fi, int nhsel)
> > int fib6_check_nexthop(struct nexthop *nh, struct fib6_config *cfg,
> > struct netlink_ext_ack *extack);
> >
> > -static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh)
> > +static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh,
> > + bool bh_disabled)
>
> Hi Wei: I would prefer not to have a second argument to nexthop_fib6_nh
> for 1 code path, and a control path at that.
>
> > {
> > struct nh_info *nhi;
> >
> > if (nh->is_group) {
> > struct nh_group *nh_grp;
> >
> > - nh_grp = rcu_dereference_rtnl(nh->nh_grp);
> > + if (bh_disabled)
> > + nh_grp = rcu_dereference_bh_rtnl(nh->nh_grp);
> > + else
> > + nh_grp = rcu_dereference_rtnl(nh->nh_grp);
> > nh = nexthop_mpath_select(nh_grp, 0);
> > if (!nh)
> > return NULL;
> > }
> >
> > - nhi = rcu_dereference_rtnl(nh->nh_info);
> > + if (bh_disabled)
> > + nhi = rcu_dereference_bh_rtnl(nh->nh_info);
> > + else
> > + nhi = rcu_dereference_rtnl(nh->nh_info);
> > if (nhi->family == AF_INET6)
> > return &nhi->fib6_nh;
> >
> > return NULL;
> > }
> >
>
> I am wary of duplicating code, but this helper is simple enough that it
> should be ok with proper documentation.
>
> Ido/Petr: I think your resilient hashing patch set touches this helper.
> How ugly does it get to have a second version?
It actually doesn't touch this helper. Looks fine to me:
diff --git a/include/net/nexthop.h b/include/net/nexthop.h
index ba94868a21d5..6df9c12546fd 100644
--- a/include/net/nexthop.h
+++ b/include/net/nexthop.h
@@ -496,6 +496,26 @@ static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh)
return NULL;
}
+static inline struct fib6_nh *nexthop_fib6_nh_bh(struct nexthop *nh)
+{
+ struct nh_info *nhi;
+
+ if (nh->is_group) {
+ struct nh_group *nh_grp;
+
+ nh_grp = rcu_dereference_bh(nh->nh_grp);
+ nh = nexthop_mpath_select(nh_grp, 0);
+ if (!nh)
+ return NULL;
+ }
+
+ nhi = rcu_dereference_bh(nh->nh_info);
+ if (nhi->family == AF_INET6)
+ return &nhi->fib6_nh;
+
+ return NULL;
+}
+
static inline struct net_device *fib6_info_nh_dev(struct fib6_info *f6i)
{
struct fib6_nh *fib6_nh;
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index ef9d022e693f..679699e953f1 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -2486,7 +2486,7 @@ static int ipv6_route_native_seq_show(struct seq_file *seq, void *v)
const struct net_device *dev;
if (rt->nh)
- fib6_nh = nexthop_fib6_nh(rt->nh);
+ fib6_nh = nexthop_fib6_nh_bh(rt->nh);
seq_printf(seq, "%pi6 %02x ", &rt->fib6_dst.addr, rt->fib6_dst.plen);
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