[PATCH v2 net] packet: Do not call fanout_release from atomic contexts

[PATCH v2 net] packet: Do not call fanout_release from atomic contexts

[Anoob Soman]

Commit 6664498280cf ("packet: call fanout_release, while UNREGISTERING a
netdev"), unfortunately, introduced the following issues.

1. calling mutex_lock(&fanout_mutex) (fanout_release()) from inside
rcu_read-side critical section. rcu_read_lock disables preemption, most often,
which prohibits calling sleeping functions.

[  ] include/linux/rcupdate.h:560 Illegal context switch in RCU read-side critical section!
[  ]
[  ] rcu_scheduler_active = 1, debug_locks = 0
[  ] 4 locks held by ovs-vswitchd/1969:
[  ]  #0:  (cb_lock){++++++}, at: [<ffffffff8158a6c9>] genl_rcv+0x19/0x40
[  ]  #1:  (ovs_mutex){+.+.+.}, at: [<ffffffffa04878ca>] ovs_vport_cmd_del+0x4a/0x100 [openvswitch]
[  ]  #2:  (rtnl_mutex){+.+.+.}, at: [<ffffffff81564157>] rtnl_lock+0x17/0x20
[  ]  #3:  (rcu_read_lock){......}, at: [<ffffffff81614165>] packet_notifier+0x5/0x3f0
[  ]
[  ] Call Trace:
[  ]  [<ffffffff813770c1>] dump_stack+0x85/0xc4
[  ]  [<ffffffff810c9077>] lockdep_rcu_suspicious+0x107/0x110
[  ]  [<ffffffff810a2da7>] ___might_sleep+0x57/0x210
[  ]  [<ffffffff810a2fd0>] __might_sleep+0x70/0x90
[  ]  [<ffffffff8162e80c>] mutex_lock_nested+0x3c/0x3a0
[  ]  [<ffffffff810de93f>] ? vprintk_default+0x1f/0x30
[  ]  [<ffffffff81186e88>] ? printk+0x4d/0x4f
[  ]  [<ffffffff816106dd>] fanout_release+0x1d/0xe0
[  ]  [<ffffffff81614459>] packet_notifier+0x2f9/0x3f0

2. calling mutex_lock(&fanout_mutex) inside spin_lock(&po->bind_lock).
"sleeping function called from invalid context"

[  ] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:620
[  ] in_atomic(): 1, irqs_disabled(): 0, pid: 1969, name: ovs-vswitchd
[  ] INFO: lockdep is turned off.
[  ] Call Trace:
[  ]  [<ffffffff813770c1>] dump_stack+0x85/0xc4
[  ]  [<ffffffff810a2f52>] ___might_sleep+0x202/0x210
[  ]  [<ffffffff810a2fd0>] __might_sleep+0x70/0x90
[  ]  [<ffffffff8162e80c>] mutex_lock_nested+0x3c/0x3a0
[  ]  [<ffffffff816106dd>] fanout_release+0x1d/0xe0
[  ]  [<ffffffff81614459>] packet_notifier+0x2f9/0x3f0

3. calling dev_remove_pack(&fanout->prot_hook), from inside
spin_lock(&po->bind_lock) or rcu_read-side critical-section. dev_remove_pack()
-> synchronize_net(), which might sleep.

[  ] BUG: scheduling while atomic: ovs-vswitchd/1969/0x00000002
[  ] INFO: lockdep is turned off.
[  ] Call Trace:
[  ]  [<ffffffff813770c1>] dump_stack+0x85/0xc4
[  ]  [<ffffffff81186274>] __schedule_bug+0x64/0x73
[  ]  [<ffffffff8162b8cb>] __schedule+0x6b/0xd10
[  ]  [<ffffffff8162c5db>] schedule+0x6b/0x80
[  ]  [<ffffffff81630b1d>] schedule_timeout+0x38d/0x410
[  ]  [<ffffffff810ea3fd>] synchronize_sched_expedited+0x53d/0x810
[  ]  [<ffffffff810ea6de>] synchronize_rcu_expedited+0xe/0x10
[  ]  [<ffffffff8154eab5>] synchronize_net+0x35/0x50
[  ]  [<ffffffff8154eae3>] dev_remove_pack+0x13/0x20
[  ]  [<ffffffff8161077e>] fanout_release+0xbe/0xe0
[  ]  [<ffffffff81614459>] packet_notifier+0x2f9/0x3f0

4. fanout_release() races with calls from different CPU.

To fix the above problems, remove the call to fanout_release() under
rcu_read_lock(). Instead, call __dev_remove_pack(&fanout->prot_hook) and
netdev_run_todo will be happy that &dev->ptype_specific list is empty. In order
to achieve this, I moved dev_{add,remove}_pack() out of fanout_{add,release} to
__fanout_{link,unlink}. So, call to {,__}unregister_prot_hook() will make sure
fanout->prot_hook is removed as well.

Fixes: 6664498280cf ("packet: call fanout_release, while UNREGISTERING a netdev")
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Anoob Soman <anoob.soman@citrix.com>
---

Changes in v2:
 - Incorporated Eric's suggestion to do fanout_release_data() and kfree() after
    synchronize_net()

 net/packet/af_packet.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index d56ee46..af29510 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1497,6 +1497,8 @@ static void __fanout_link(struct sock *sk, struct packet_sock *po)
 	f->arr[f->num_members] = sk;
 	smp_wmb();
 	f->num_members++;
+	if (f->num_members == 1)
+		dev_add_pack(&f->prot_hook);
 	spin_unlock(&f->lock);
 }
 
@@ -1513,6 +1515,8 @@ static void __fanout_unlink(struct sock *sk, struct packet_sock *po)
 	BUG_ON(i >= f->num_members);
 	f->arr[i] = f->arr[f->num_members - 1];
 	f->num_members--;
+	if (f->num_members == 0)
+		__dev_remove_pack(&f->prot_hook);
 	spin_unlock(&f->lock);
 }
 
@@ -1687,7 +1691,6 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
 		match->prot_hook.func = packet_rcv_fanout;
 		match->prot_hook.af_packet_priv = match;
 		match->prot_hook.id_match = match_fanout_group;
-		dev_add_pack(&match->prot_hook);
 		list_add(&match->list, &fanout_list);
 	}
 	err = -EINVAL;
@@ -1712,10 +1715,16 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
 	return err;
 }
 
-static void fanout_release(struct sock *sk)
+/* If pkt_sk(sk)->fanout->sk_ref is zero, this functuon removes
+ * pkt_sk(sk)->fanout from fanout_list and returns pkt_sk(sk)->fanout.
+ * It is the responsibility of the caller to call fanout_release_data() and
+ * free the returned packet_fanout (after synchronize_net())
+ */
+static struct packet_fanout *fanout_release(struct sock *sk)
 {
 	struct packet_sock *po = pkt_sk(sk);
 	struct packet_fanout *f;
+	bool ret_fanout = false;
 
 	f = po->fanout;
 	if (!f)
@@ -1726,14 +1735,14 @@ static void fanout_release(struct sock *sk)
 
 	if (atomic_dec_and_test(&f->sk_ref)) {
 		list_del(&f->list);
-		dev_remove_pack(&f->prot_hook);
-		fanout_release_data(f);
-		kfree(f);
+		ret_fanout = true;
 	}
 	mutex_unlock(&fanout_mutex);
 
 	if (po->rollover)
 		kfree_rcu(po->rollover, rcu);
+
+	return ret_fanout ? f : NULL;
 }
 
 static bool packet_extra_vlan_len_allowed(const struct net_device *dev,
@@ -2907,6 +2916,7 @@ static int packet_release(struct socket *sock)
 {
 	struct sock *sk = sock->sk;
 	struct packet_sock *po;
+	struct packet_fanout *f;
 	struct net *net;
 	union tpacket_req_u req_u;
 
@@ -2946,9 +2956,15 @@ static int packet_release(struct socket *sock)
 		packet_set_ring(sk, &req_u, 1, 1);
 	}
 
-	fanout_release(sk);
+	f = fanout_release(sk);
 
 	synchronize_net();
+
+	if (f) {
+		fanout_release_data(f);
+		kfree(f);
+	}
+
 	/*
 	 *	Now the socket is dead. No more input will appear.
 	 */
@@ -3900,7 +3916,6 @@ static int packet_notifier(struct notifier_block *this,
 				}
 				if (msg == NETDEV_UNREGISTER) {
 					packet_cached_dev_reset(po);
-					fanout_release(sk);
 					po->ifindex = -1;
 					if (po->prot_hook.dev)
 						dev_put(po->prot_hook.dev);
-- 
2.7.4

Re: [PATCH v2 net] packet: Do not call fanout_release from atomic contexts

[kbuild test robot]

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Hi Anoob,

[auto build test WARNING on net-next/master]
[also build test WARNING on v4.10-rc8]
[cannot apply to net/master next-20170215]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Anoob-Soman/packet-Do-not-call-fanout_release-from-atomic-contexts/20170216-004744
config: x86_64-randconfig-x008-201707 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   net/packet/af_packet.c: In function 'fanout_release':
>> net/packet/af_packet.c:1739:3: warning: 'return' with no value, in function returning non-void [-Wreturn-type]
      return;
      ^~~~~~
   net/packet/af_packet.c:1731:30: note: declared here
    static struct packet_fanout *fanout_release(struct sock *sk)
                                 ^~~~~~~~~~~~~~

vim +/return +1739 net/packet/af_packet.c

dc99f600 David S. Miller 2011-07-05  1723  	return err;
dc99f600 David S. Miller 2011-07-05  1724  }
dc99f600 David S. Miller 2011-07-05  1725  
53d5c353 Anoob Soman     2017-02-15  1726  /* If pkt_sk(sk)->fanout->sk_ref is zero, this functuon removes
53d5c353 Anoob Soman     2017-02-15  1727   * pkt_sk(sk)->fanout from fanout_list and returns pkt_sk(sk)->fanout.
53d5c353 Anoob Soman     2017-02-15  1728   * It is the responsibility of the caller to call fanout_release_data() and
53d5c353 Anoob Soman     2017-02-15  1729   * free the returned packet_fanout (after synchronize_net())
53d5c353 Anoob Soman     2017-02-15  1730   */
53d5c353 Anoob Soman     2017-02-15  1731  static struct packet_fanout *fanout_release(struct sock *sk)
dc99f600 David S. Miller 2011-07-05  1732  {
dc99f600 David S. Miller 2011-07-05  1733  	struct packet_sock *po = pkt_sk(sk);
dc99f600 David S. Miller 2011-07-05  1734  	struct packet_fanout *f;
53d5c353 Anoob Soman     2017-02-15  1735  	bool ret_fanout = false;
dc99f600 David S. Miller 2011-07-05  1736  
dc99f600 David S. Miller 2011-07-05  1737  	f = po->fanout;
dc99f600 David S. Miller 2011-07-05  1738  	if (!f)
dc99f600 David S. Miller 2011-07-05 @1739  		return;
dc99f600 David S. Miller 2011-07-05  1740  
fff3321d Pavel Emelyanov 2012-08-16  1741  	mutex_lock(&fanout_mutex);
dc99f600 David S. Miller 2011-07-05  1742  	po->fanout = NULL;
dc99f600 David S. Miller 2011-07-05  1743  
dc99f600 David S. Miller 2011-07-05  1744  	if (atomic_dec_and_test(&f->sk_ref)) {
dc99f600 David S. Miller 2011-07-05  1745  		list_del(&f->list);
53d5c353 Anoob Soman     2017-02-15  1746  		ret_fanout = true;
dc99f600 David S. Miller 2011-07-05  1747  	}

:::::: The code at line 1739 was first introduced by commit
:::::: dc99f600698dcac69b8f56dda9a8a00d645c5ffc packet: Add fanout support.

:::::: TO: David S. Miller <davem@davemloft.net>
:::::: CC: David S. Miller <davem@davemloft.net>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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Re: [PATCH v2 net] packet: Do not call fanout_release from atomic contexts

[Eric Dumazet]

On Wed, 2017-02-15 at 16:43 +0000, Anoob Soman wrote:

> 
>  net/packet/af_packet.c | 29 ++++++++++++++++++++++-------
>  1 file changed, 22 insertions(+), 7 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index d56ee46..af29510 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -1497,6 +1497,8 @@ static void __fanout_link(struct sock *sk, struct packet_sock *po)
>  	f->arr[f->num_members] = sk;
>  	smp_wmb();
>  	f->num_members++;
> +	if (f->num_members == 1)
> +		dev_add_pack(&f->prot_hook);
>  	spin_unlock(&f->lock);
>  }
>  
> @@ -1513,6 +1515,8 @@ static void __fanout_unlink(struct sock *sk, struct packet_sock *po)
>  	BUG_ON(i >= f->num_members);
>  	f->arr[i] = f->arr[f->num_members - 1];
>  	f->num_members--;
> +	if (f->num_members == 0)
> +		__dev_remove_pack(&f->prot_hook);
>  	spin_unlock(&f->lock);
>  }
>  
> @@ -1687,7 +1691,6 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
>  		match->prot_hook.func = packet_rcv_fanout;
>  		match->prot_hook.af_packet_priv = match;
>  		match->prot_hook.id_match = match_fanout_group;
> -		dev_add_pack(&match->prot_hook);
>  		list_add(&match->list, &fanout_list);
>  	}
>  	err = -EINVAL;
> @@ -1712,10 +1715,16 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
>  	return err;
>  }
>  
> -static void fanout_release(struct sock *sk)
> +/* If pkt_sk(sk)->fanout->sk_ref is zero, this functuon removes
> + * pkt_sk(sk)->fanout from fanout_list and returns pkt_sk(sk)->fanout.
> + * It is the responsibility of the caller to call fanout_release_data() and
> + * free the returned packet_fanout (after synchronize_net())
> + */
> +static struct packet_fanout *fanout_release(struct sock *sk)
>  {
>  	struct packet_sock *po = pkt_sk(sk);
>  	struct packet_fanout *f;
> +	bool ret_fanout = false;

No need for this new variable.

>  
>  	f = po->fanout;
>  	if (!f)
> @@ -1726,14 +1735,14 @@ static void fanout_release(struct sock *sk)
>  
>  	if (atomic_dec_and_test(&f->sk_ref)) {
>  		list_del(&f->list);
> -		dev_remove_pack(&f->prot_hook);
> -		fanout_release_data(f);
> -		kfree(f);
> +		ret_fanout = true;
>  	}

} else {
     f = NULL;
}

>  	mutex_unlock(&fanout_mutex);
>  
>  	if (po->rollover)
>  		kfree_rcu(po->rollover, rcu);
> +
> +	return ret_fanout ? f : NULL;

return f;

>  }
>  
>  

Otherwise, this look good.

But make sure to respin your patch based on latest net tree.

af_packet.c got a recent fix.

Thanks