Subject: Re: Bridge VLAN memory leak

From: Vlad Buslov <[email-masked]>
Date: Tue, 5 Jul 2022 19:25:14 +0300

On Tue 05 Jul 2022 at 18:42, Ido Schimmel <[email-masked]> wrote:
> On Tue, Jul 05, 2022 at 05:46:49PM +0300, Vlad Buslov wrote:
>> On Tue 05 Jul 2022 at 16:55, Ido Schimmel <[email-masked]> wrote:
>> > On Mon, Jul 04, 2022 at 06:47:29PM +0300, Vlad Buslov wrote:
>> >> Hi Ido,
>> >> 
>> >> While implementing QinQ offload support in mlx5 I encountered a memory
>> >> leak[0] in the bridge implementation which seems to be related to the new
>> >> BR_VLFLAG_ADDED_BY_SWITCHDEV flag that you have recently added.
>> >
>> > FTR, added here:
>> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=279737939a8194f02fa352ab4476a1b241f44ef4
>> >
>> >> 
>> >> To reproduce the issue netdevice must support bridge VLAN offload, so I
>> >> can't provide a simple script that uses veth or anything like that.
>> >> Instead, I'll describe the issue step-by-step:
>> >> 
>> >> 1. Create a bridge, add offload-capable netdevs to it and assign some
>> >> VLAN to them. __vlan_vid_add() function will set the
>> >> BR_VLFLAG_ADDED_BY_SWITCHDEV flag since br_switchdev_port_vlan_add()
>> >> should return 0 if dev can offload VLANs and will also skip call to
>> >> vlan_vid_add() in such case:
>> >> 
>> >>         /* Try switchdev op first. In case it is not supported, fallback to
>> >>          * 8021q add.
>> >>          */
>> >>         err = br_switchdev_port_vlan_add(dev, v->vid, flags, false, extack);
>> >>         if (err == -EOPNOTSUPP)
>> >>                 return vlan_vid_add(dev, br->vlan_proto, v->vid);
>> >>         v->priv_flags |= BR_VLFLAG_ADDED_BY_SWITCHDEV;
>> >> 
>> >> 2. Enable filtering and set VLAN protocol to 802.1ad. That will trigger
>> >> the following code in __br_vlan_set_proto() that re-creates existing
>> >> VLANs with vlan_vid_add() function call whether they have the
>> >> BR_VLFLAG_ADDED_BY_SWITCHDEV flag set or not:
>> >> 
>> >>          /* Add VLANs for the new proto to the device filter. */
>> >>          list_for_each_entry(p, &br->port_list, list) {
>> >>                  vg = nbp_vlan_group(p);
>> >>                  list_for_each_entry(vlan, &vg->vlan_list, vlist) {
>> >>                          err = vlan_vid_add(p->dev, proto, vlan->vid);
>> >>                          if (err)
>> >>                                  goto err_filt;
>> >>                  }
>> >>          }
>> >> 
>> >> 3. Now delete the bridge. That will delete all existing VLANs via
>> >> __vlan_vid_del() function, which skips calling vlan_vid_del() (that is
>> >> necessary to clean up after vlan_vid_add()) if VLAN has
>> >> BR_VLFLAG_ADDED_BY_SWITCHDEV flag set:
>> >> 
>> >>          /* Try switchdev op first. In case it is not supported, fallback to
>> >>           * 8021q del.
>> >>           */
>> >>          err = br_switchdev_port_vlan_del(dev, v->vid);
>> >>          if (!(v->priv_flags & BR_VLFLAG_ADDED_BY_SWITCHDEV))
>> >>                  vlan_vid_del(dev, br->vlan_proto, v->vid);
>> >
>> > Looking at the code before the change, I'm pretty sure you will be able
>> > to reproduce the leak prior to above mentioned commit:
>> >
>> > ```
>> > -	err = br_switchdev_port_vlan_del(dev, vid);
>> > -	if (err == -EOPNOTSUPP) {
>> > -		vlan_vid_del(dev, br->vlan_proto, vid);
>> > -		return 0;
>> > -	}
>> > -	return err;
>> > ```
>> >
>> >> 
>> >> 
>> >> The issue doesn't reproduce for me anymore if I just clear the
>> >> BR_VLFLAG_ADDED_BY_SWITCHDEV flag when re-creating VLANs on step 2.
>> >> However, I'm not sure whether it is the right approach in this case.
>> >> WDYT?
>> >
>> > As a switchdev driver you already know about the new VLAN protocol via
>> > 'SWITCHDEV_ATTR_ID_BRIDGE_VLAN_PROTOCOL' so do we really need the VLANs
>> > to be programmed again? The VLAN protocol is not communicated in
>> > 'SWITCHDEV_OBJ_ID_PORT_VLAN' anyway.
>> 
>> In my WIP implementation of 802.1ad offload I just re-create all
>> existing VLANs in hardware with new protocol upon receiving
>> SWITCHDEV_ATTR_ID_BRIDGE_VLAN_PROTOCOL notification.
>
> Would it be easier for you if you got the VLAN protocol in
> 'SWITCHDEV_OBJ_ID_PORT_VLAN' and __br_vlan_set_proto() would invoke
> __vlan_vid_add() and __vlan_vid_del() instead of calling the 8021q
> driver directly?

For me it is easy to iterate and re-create existing VLANs with new
protocol inside the driver since I already have all the necessary
structures for that. Also, with current architecture I pre-create
required flow groups based on current bridge VLAN proto (during new
bridge creation or on reception of
SWITCHDEV_ATTR_ID_BRIDGE_VLAN_PROTOCOL event), so having protocol inside
switchdev_obj_port_vlan will be redundant.

>
>> 
>> >
>> > Can you try the below (compile tested only)?
>> 
>> With the patch applied memleak no longer reproduces.
>> 
>> >
>> > ```
>> > diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
>> > index 6e53dc991409..9ffd40b8270c 100644
>> > --- a/net/bridge/br_vlan.c
>> > +++ b/net/bridge/br_vlan.c
>> > @@ -959,6 +959,8 @@ int __br_vlan_set_proto(struct net_bridge *br, __be16 proto,
>> >  	list_for_each_entry(p, &br->port_list, list) {
>> >  		vg = nbp_vlan_group(p);
>> >  		list_for_each_entry(vlan, &vg->vlan_list, vlist) {
>> > +			if (vlan->priv_flags & BR_VLFLAG_ADDED_BY_SWITCHDEV)
>> > +				continue;
>> >  			err = vlan_vid_add(p->dev, proto, vlan->vid);
>> >  			if (err)
>> >  				goto err_filt;
>> > @@ -973,8 +975,11 @@ int __br_vlan_set_proto(struct net_bridge *br, __be16 proto,
>> >  	/* Delete VLANs for the old proto from the device filter. */
>> >  	list_for_each_entry(p, &br->port_list, list) {
>> >  		vg = nbp_vlan_group(p);
>> > -		list_for_each_entry(vlan, &vg->vlan_list, vlist)
>> > +		list_for_each_entry(vlan, &vg->vlan_list, vlist) {
>> > +			if (vlan->priv_flags & BR_VLFLAG_ADDED_BY_SWITCHDEV)
>> > +				continue;
>> >  			vlan_vid_del(p->dev, oldproto, vlan->vid);
>> > +		}
>> >  	}
>> >  
>> >  	return 0;
>> > @@ -983,13 +988,19 @@ int __br_vlan_set_proto(struct net_bridge *br, __be16 proto,
>> >  	attr.u.vlan_protocol = ntohs(oldproto);
>> >  	switchdev_port_attr_set(br->dev, &attr, NULL);
>> >  
>> > -	list_for_each_entry_continue_reverse(vlan, &vg->vlan_list, vlist)
>> > +	list_for_each_entry_continue_reverse(vlan, &vg->vlan_list, vlist) {
>> > +		if (vlan->priv_flags & BR_VLFLAG_ADDED_BY_SWITCHDEV)
>> > +			continue;
>> >  		vlan_vid_del(p->dev, proto, vlan->vid);
>> > +	}
>> >  
>> >  	list_for_each_entry_continue_reverse(p, &br->port_list, list) {
>> >  		vg = nbp_vlan_group(p);
>> > -		list_for_each_entry(vlan, &vg->vlan_list, vlist)
>> > +		list_for_each_entry(vlan, &vg->vlan_list, vlist) {
>> > +			if (vlan->priv_flags & BR_VLFLAG_ADDED_BY_SWITCHDEV)
>> > +				continue;
>> >  			vlan_vid_del(p->dev, proto, vlan->vid);
>> > +		}
>> >  	}
>> >  
>> >  	return err;
>> > ```
>> >
>> >> 
>> >> [0]:
>> >> 
>> >> unreferenced object 0xffff8881f6771200 (size 256):
>> >>   comm "ip", pid 446855, jiffies 4298238841 (age 55.240s)
>> >>   hex dump (first 32 bytes):
>> >>     00 00 7f 0e 83 88 ff ff 00 00 00 00 00 00 00 00  ................
>> >>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>> >>   backtrace:
>> >>     [<00000000012819ac>] vlan_vid_add+0x437/0x750
>> >>     [<00000000f2281fad>] __br_vlan_set_proto+0x289/0x920
>> >>     [<000000000632b56f>] br_changelink+0x3d6/0x13f0
>> >>     [<0000000089d25f04>] __rtnl_newlink+0x8ae/0x14c0
>> >>     [<00000000f6276baf>] rtnl_newlink+0x5f/0x90
>> >>     [<00000000746dc902>] rtnetlink_rcv_msg+0x336/0xa00
>> >>     [<000000001c2241c0>] netlink_rcv_skb+0x11d/0x340
>> >>     [<0000000010588814>] netlink_unicast+0x438/0x710
>> >>     [<00000000e1a4cd5c>] netlink_sendmsg+0x788/0xc40
>> >>     [<00000000e8992d4e>] sock_sendmsg+0xb0/0xe0
>> >>     [<00000000621b8f91>] ____sys_sendmsg+0x4ff/0x6d0
>> >>     [<000000000ea26996>] ___sys_sendmsg+0x12e/0x1b0
>> >>     [<00000000684f7e25>] __sys_sendmsg+0xab/0x130
>> >>     [<000000004538b104>] do_syscall_64+0x3d/0x90
>> >>     [<0000000091ed9678>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
>> >> 
>> >> 
>> >> Regards,
>> >> Vlad
>>