netdev - Re: [PATCH net] net: bridge: Fix a warning when del bridge sysfs

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Date:   Wed, 2 Dec 2020 17:03:59 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Wang Hai <wanghai38@...wei.com>
Cc:     <roopa@...dia.com>, <nikolay@...dia.com>, <davem@...emloft.net>,
        <bridge@...ts.linux-foundation.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: bridge: Fix a warning when del bridge sysfs

On Tue, 1 Dec 2020 22:01:14 +0800 Wang Hai wrote:
> If adding bridge sysfs fails, br->ifobj will be NULL, there is no
> need to delete its non-existent sysfs when deleting the bridge device,
> otherwise, it will cause a warning. So, when br->ifobj == NULL,
> directly return can fix this bug.
> 
> br_sysfs_addbr: can't create group bridge4/bridge
> ------------[ cut here ]------------
> sysfs group 'bridge' not found for kobject 'bridge4'
> WARNING: CPU: 2 PID: 9004 at fs/sysfs/group.c:279 sysfs_remove_group fs/sysfs/group.c:279 [inline]
> WARNING: CPU: 2 PID: 9004 at fs/sysfs/group.c:279 sysfs_remove_group+0x153/0x1b0 fs/sysfs/group.c:270
> Modules linked in: iptable_nat
> ...
> Call Trace:
>   br_dev_delete+0x112/0x190 net/bridge/br_if.c:384
>   br_dev_newlink net/bridge/br_netlink.c:1381 [inline]
>   br_dev_newlink+0xdb/0x100 net/bridge/br_netlink.c:1362
>   __rtnl_newlink+0xe11/0x13f0 net/core/rtnetlink.c:3441
>   rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3500
>   rtnetlink_rcv_msg+0x385/0x980 net/core/rtnetlink.c:5562
>   netlink_rcv_skb+0x134/0x3d0 net/netlink/af_netlink.c:2494
>   netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
>   netlink_unicast+0x4a0/0x6a0 net/netlink/af_netlink.c:1330
>   netlink_sendmsg+0x793/0xc80 net/netlink/af_netlink.c:1919
>   sock_sendmsg_nosec net/socket.c:651 [inline]
>   sock_sendmsg+0x139/0x170 net/socket.c:671
>   ____sys_sendmsg+0x658/0x7d0 net/socket.c:2353
>   ___sys_sendmsg+0xf8/0x170 net/socket.c:2407
>   __sys_sendmsg+0xd3/0x190 net/socket.c:2440
>   do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Reported-by: Hulk Robot <hulkci@...wei.com>
> Signed-off-by: Wang Hai <wanghai38@...wei.com>

Nik, is this the way you want to handle this?

Should the notifier not fail if sysfs files cannot be created?
Currently br_sysfs_addbr() returns an int but the only caller 
ignores it.

> diff --git a/net/bridge/br_sysfs_br.c b/net/bridge/br_sysfs_br.c
> index 7db06e3f642a..1e9cbf31d904 100644
> --- a/net/bridge/br_sysfs_br.c
> +++ b/net/bridge/br_sysfs_br.c
> @@ -991,6 +991,9 @@ void br_sysfs_delbr(struct net_device *dev)
>  	struct kobject *kobj = &dev->dev.kobj;
>  	struct net_bridge *br = netdev_priv(dev);
>  
> +	if (!br->ifobj)
> +		return;
> +
>  	kobject_put(br->ifobj);
>  	sysfs_remove_bin_file(kobj, &bridge_forward);
>  	sysfs_remove_group(kobj, &bridge_group);