netdev - Re: [Patch net] ipvlan: use rcu_deference_bh() in ipvlan_queue

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Date:	Tue, 19 May 2015 16:31:49 -0700
From:	Mahesh Bandewar <maheshb@...gle.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	linux-netdev <netdev@...r.kernel.org>
Subject: Re: [Patch net] ipvlan: use rcu_deference_bh() in ipvlan_queue_xmit()

On Tue, May 12, 2015 at 11:46 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> In tx path rcu_read_lock_bh() is held, so we need rcu_deference_bh().
> This fixes the following warning:
>
>  ===============================
>  [ INFO: suspicious RCU usage. ]
>  4.1.0-rc1+ #1007 Not tainted
>  -------------------------------
>  drivers/net/ipvlan/ipvlan.h:106 suspicious rcu_dereference_check() usage!
>
>  other info that might help us debug this:
>
>  rcu_scheduler_active = 1, debug_locks = 0
>  1 lock held by dhclient/1076:
>   #0:  (rcu_read_lock_bh){......}, at: [<ffffffff817e8d84>] rcu_lock_acquire+0x0/0x26
>
>  stack backtrace:
>  CPU: 2 PID: 1076 Comm: dhclient Not tainted 4.1.0-rc1+ #1007
>  Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
>   0000000000000001 ffff8800d381bac8 ffffffff81a4154f 000000003c1a3c19
>   ffff8800d4d0a690 ffff8800d381baf8 ffffffff810b849f ffff880117d41148
>   ffff880117d40000 ffff880117d40068 0000000000000156 ffff8800d381bb18
>  Call Trace:
>   [<ffffffff81a4154f>] dump_stack+0x4c/0x65
>   [<ffffffff810b849f>] lockdep_rcu_suspicious+0x107/0x110
>   [<ffffffff8165a522>] ipvlan_port_get_rcu+0x47/0x4e
>   [<ffffffff8165ad14>] ipvlan_queue_xmit+0x35/0x450
>   [<ffffffff817ea45d>] ? rcu_read_unlock+0x3e/0x5f
>   [<ffffffff810a20bf>] ? local_clock+0x19/0x22
>   [<ffffffff810b4781>] ? __lock_is_held+0x39/0x52
>   [<ffffffff8165b64c>] ipvlan_start_xmit+0x1b/0x44
>   [<ffffffff817edf7f>] dev_hard_start_xmit+0x2ae/0x467
>   [<ffffffff817ee642>] __dev_queue_xmit+0x50a/0x60c
>   [<ffffffff817ee7a7>] dev_queue_xmit_sk+0x13/0x15
>   [<ffffffff81997596>] dev_queue_xmit+0x10/0x12
>   [<ffffffff8199b41c>] packet_sendmsg+0xb6b/0xbdf
>   [<ffffffff810b5ea7>] ? mark_lock+0x2e/0x226
>   [<ffffffff810a1fcc>] ? sched_clock_cpu+0x9e/0xb7
>   [<ffffffff817d56f9>] sock_sendmsg_nosec+0x12/0x1d
>   [<ffffffff817d7257>] sock_sendmsg+0x29/0x2e
>   [<ffffffff817d72cc>] sock_write_iter+0x70/0x91
>   [<ffffffff81199563>] __vfs_write+0x7e/0xa7
>   [<ffffffff811996bc>] vfs_write+0x92/0xe8
>   [<ffffffff811997d7>] SyS_write+0x47/0x7e
>   [<ffffffff81a4d517>] system_call_fastpath+0x12/0x6f
>
> Fixes: 2ad7bf363841 ("ipvlan: Initial check-in of the IPVLAN driver.")
> Cc: Mahesh Bandewar <maheshb@...gle.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
Acked-by: Mahesh Bandewar <maheshb@...gle.com>
> ---
>  drivers/net/ipvlan/ipvlan.h      | 5 +++++
>  drivers/net/ipvlan/ipvlan_core.c | 2 +-
>  2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ipvlan/ipvlan.h b/drivers/net/ipvlan/ipvlan.h
> index 54549a6..0799442 100644
> --- a/drivers/net/ipvlan/ipvlan.h
> +++ b/drivers/net/ipvlan/ipvlan.h
> @@ -102,6 +102,11 @@ static inline struct ipvl_port *ipvlan_port_get_rcu(const struct net_device *d)
>         return rcu_dereference(d->rx_handler_data);
>  }
>
> +static inline struct ipvl_port *ipvlan_port_get_rcu_bh(const struct net_device *d)
> +{
> +       return rcu_dereference_bh(d->rx_handler_data);
> +}
> +
>  static inline struct ipvl_port *ipvlan_port_get_rtnl(const struct net_device *d)
>  {
>         return rtnl_dereference(d->rx_handler_data);
> diff --git a/drivers/net/ipvlan/ipvlan_core.c b/drivers/net/ipvlan/ipvlan_core.c
> index c30b5c3..b349dad 100644
> --- a/drivers/net/ipvlan/ipvlan_core.c
> +++ b/drivers/net/ipvlan/ipvlan_core.c
> @@ -507,7 +507,7 @@ static int ipvlan_xmit_mode_l2(struct sk_buff *skb, struct net_device *dev)
>  int ipvlan_queue_xmit(struct sk_buff *skb, struct net_device *dev)
>  {
>         struct ipvl_dev *ipvlan = netdev_priv(dev);
> -       struct ipvl_port *port = ipvlan_port_get_rcu(ipvlan->phy_dev);
> +       struct ipvl_port *port = ipvlan_port_get_rcu_bh(ipvlan->phy_dev);
>
>         if (!port)
>                 goto out;
> --
> 1.8.3.1
>
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