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Date: Fri, 22 Jul 2022 22:37:24 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Vladimir Oltean <olteanv@...il.com>
Cc: "David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
netdev <netdev@...r.kernel.org>,
Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v2 net-next 08/19] ipmr: do not acquire mrt_lock while
calling ip_mr_forward()
On Fri, Jul 22, 2022 at 9:34 PM Vladimir Oltean <olteanv@...il.com> wrote:
>
> Hi Eric,
>
> On Thu, Jun 23, 2022 at 04:34:38AM +0000, Eric Dumazet wrote:
> > ip_mr_forward() uses standard RCU protection already.
> >
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > ---
> > net/ipv4/ipmr.c | 9 ++-------
> > 1 file changed, 2 insertions(+), 7 deletions(-)
> >
> > diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
> > index 6ea54bc3d9b6555aaa9974d81ba4acd47481724f..b0f2e6d79d62273c8c2682f28cb45fe5ec3df6f3 100644
> > --- a/net/ipv4/ipmr.c
> > +++ b/net/ipv4/ipmr.c
> > @@ -1817,7 +1817,7 @@ static bool ipmr_forward_offloaded(struct sk_buff *skb, struct mr_table *mrt,
> > }
> > #endif
> >
> > -/* Processing handlers for ipmr_forward */
> > +/* Processing handlers for ipmr_forward, under rcu_read_lock() */
> >
> > static void ipmr_queue_xmit(struct net *net, struct mr_table *mrt,
> > int in_vifi, struct sk_buff *skb, int vifi)
> > @@ -1839,9 +1839,7 @@ static void ipmr_queue_xmit(struct net *net, struct mr_table *mrt,
> > WRITE_ONCE(vif->bytes_out, vif->bytes_out + skb->len);
> > vif_dev->stats.tx_bytes += skb->len;
> > vif_dev->stats.tx_packets++;
> > - rcu_read_lock();
> > ipmr_cache_report(mrt, skb, vifi, IGMPMSG_WHOLEPKT);
> > - rcu_read_unlock();
> > goto out_free;
> > }
> >
> > @@ -1936,6 +1934,7 @@ static int ipmr_find_vif(const struct mr_table *mrt, struct net_device *dev)
> > }
> >
> > /* "local" means that we should preserve one skb (for local delivery) */
> > +/* Called uner rcu_read_lock() */
> > static void ip_mr_forward(struct net *net, struct mr_table *mrt,
> > struct net_device *dev, struct sk_buff *skb,
> > struct mfc_cache *c, int local)
> > @@ -1992,12 +1991,10 @@ static void ip_mr_forward(struct net *net, struct mr_table *mrt,
> > c->_c.mfc_un.res.last_assert +
> > MFC_ASSERT_THRESH)) {
> > c->_c.mfc_un.res.last_assert = jiffies;
> > - rcu_read_lock();
> > ipmr_cache_report(mrt, skb, true_vifi, IGMPMSG_WRONGVIF);
> > if (mrt->mroute_do_wrvifwhole)
> > ipmr_cache_report(mrt, skb, true_vifi,
> > IGMPMSG_WRVIFWHOLE);
> > - rcu_read_unlock();
> > }
> > goto dont_forward;
> > }
> > @@ -2169,9 +2166,7 @@ int ip_mr_input(struct sk_buff *skb)
> > return -ENODEV;
> > }
> >
> > - read_lock(&mrt_lock);
> > ip_mr_forward(net, mrt, dev, skb, cache, local);
> > - read_unlock(&mrt_lock);
> >
> > if (local)
> > return ip_local_deliver(skb);
> > --
> > 2.37.0.rc0.104.g0611611a94-goog
> >
>
> Sorry for reporting this late, but there seems to be 1 call path from
> which RCU is not watching in ip_mr_forward(). It's via ipmr_mfc_add() ->
> ipmr_cache_resolve() -> ip_mr_forward().
>
> The warning looks like this:
>
> [ 632.062382] =============================
> [ 632.068568] WARNING: suspicious RCU usage
> [ 632.073702] 5.19.0-rc7-07010-ga9b9500ffaac-dirty #3374 Not tainted
> [ 632.081098] -----------------------------
> [ 632.086216] net/ipv4/ipmr.c:1080 suspicious rcu_dereference_check() usage!
> [ 632.094152]
> [ 632.094152] other info that might help us debug this:
> [ 632.103349]
> [ 632.103349] rcu_scheduler_active = 2, debug_locks = 1
> [ 632.111011] 1 lock held by smcrouted/359:
> [ 632.116079] #0: ffffd27b44d23770 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock+0x1c/0x30
> [ 632.124703]
> [ 632.124703] stack backtrace:
> [ 632.129681] CPU: 0 PID: 359 Comm: smcrouted Not tainted 5.19.0-rc7-07010-ga9b9500ffaac-dirty #3374
> [ 632.143426] Call trace:
> [ 632.160542] lockdep_rcu_suspicious+0xf8/0x10c
> [ 632.165014] ipmr_cache_report+0x2f0/0x530
> [ 632.169137] ip_mr_forward+0x364/0x38c
> [ 632.172909] ipmr_mfc_add+0x894/0xc90
> [ 632.176592] ip_mroute_setsockopt+0x6ac/0x950
> [ 632.180973] ip_setsockopt+0x16a0/0x16ac
> [ 632.184921] raw_setsockopt+0x110/0x184
> [ 632.188780] sock_common_setsockopt+0x1c/0x2c
> [ 632.193163] __sys_setsockopt+0x94/0x170
> [ 632.197111] __arm64_sys_setsockopt+0x2c/0x40
> [ 632.201492] invoke_syscall+0x48/0x114
>
> I don't exactly understand the data structures that are used inside ip_mr_forward(),
> so I'm unable to say what needs RCU protection and what is fine with the rtnl_mutex
> that we are holding, just annotated poorly. Could you please take a look?
Thanks for the report.
I guess there are multiple ways to solve this issue, one being:
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 73651d17e51f31c8755da6ac3c1c2763a99b1117..1c288a7b60132365c072874d1f811b70679a2bcb
100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1004,7 +1004,9 @@ static void ipmr_cache_resolve(struct net *net,
struct mr_table *mrt,
rtnl_unicast(skb, net, NETLINK_CB(skb).portid);
} else {
+ rcu_read_lock();
ip_mr_forward(net, mrt, skb->dev, skb, c, 0);
+ rcu_read_unlock();
}
}
}
@@ -1933,7 +1935,7 @@ static int ipmr_find_vif(const struct mr_table
*mrt, struct net_device *dev)
}
/* "local" means that we should preserve one skb (for local delivery) */
-/* Called uner rcu_read_lock() */
+/* Called under rcu_read_lock() */
static void ip_mr_forward(struct net *net, struct mr_table *mrt,
struct net_device *dev, struct sk_buff *skb,
struct mfc_cache *c, int local)
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