netdev - Re: [PATCH v2] vxlan: remove the redundant gro_cells

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Date:   Sat, 16 Mar 2019 06:45:07 +0100
From:   Stefano Brivio <sbrivio@...hat.com>
To:     Zhiqiang Liu <liuzhiqiang26@...wei.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>, <petrm@...lanox.com>,
        <idosch@...lanox.com>, <sd@...asysnail.net>,
        <mousuanming@...wei.com>, <netdev@...r.kernel.org>,
        <mingfangsen@...wei.com>, <zhoukang7@...wei.com>,
        <wangxiaogang3@...wei.com>
Subject: Re: [PATCH v2] vxlan: remove the redundant gro_cells_destroy()
 calling.

On Sat, 16 Mar 2019 13:24:39 +0800
Zhiqiang Liu <liuzhiqiang26@...wei.com> wrote:

> I have updated the commit message as suggested by Eric. Even though I have read
> Documentation/networking/netdev-FAQ.rst as you mentioned. I am now still a little
> confused about the subject-prefix of v3 (net or net-next).

It's "net": this is a (likely critical) fix.

> And David Miller saied the net-next tree is CLOSED.

Right, but this is not for net-next anymore, given what Eric found.

> Could you help me check whether the following v3 patch is ok?
> 
> 
> Subject: [PATCH net v3] vxlan: remove the redundant gro_cells_destroy() calling.

This one. And it's not just redundant, so maybe something like:

	"[PATCH net v3] vxlan: Don't call gro_cells_destroy() before
	device is unregistered"

> OR
> Subject: [PATCH net-next v3] vxlan: remove the redundant gro_cells_destroy() calling.
> 
> Commit ad6c9986bcb62 ("vxlan: Fix GRO cells race condition between
> receive and link delete") fixed a race condition for the typical case a vxlan
> device is dismantled from the current netns. But if a netns is dismantled,
> vxlan_destroy_tunnels() is called to schedule a unregister_netdevice_queue()
> of all the vxlan tunnels that are related to this netns.
> 
> In vxlan_destroy_tunnels(), gro_cells_destroy() is called and finished before
> unregister_netdevice_queue(). This means that the gro_cells_destroy() call is
> done too soon, for the same reasons explained in above commit.
> 
> So we need to fully respect the RCU rules, and thus must remove the
> gro_cells_destroy() call or risk use after-free.
> 
> Fixes: 58ce31cca1ff ("vxlan: GRO support at tunnel layer")
> Signed-off-by: Suanming.Mou <mousuanming@...wei.com>
> Suggested-by: Eric Dumazet <eric.dumazet@...il.com>
> Reviewed-by: Stefano Brivio <sbrivio@...hat.com>
> Reviewed-by: Zhiqiang Liu <liuzhiqiang26@...wei.com>
> ---
> V1->V2:

This will actually be v3.

> 	- update the commit message suggeted by Eric Dumazet
> 	- update Fixes: tag
> 
>  drivers/net/vxlan.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
> index 077f1b9f2761..d76dfed8d9bb 100644
> --- a/drivers/net/vxlan.c
> +++ b/drivers/net/vxlan.c
> @@ -4335,10 +4335,8 @@ static void vxlan_destroy_tunnels(struct net *net, struct list_head *head)
>  		/* If vxlan->dev is in the same netns, it has already been added
>  		 * to the list by the previous loop.
>  		 */
> -		if (!net_eq(dev_net(vxlan->dev), net)) {
> -			gro_cells_destroy(&vxlan->gro_cells);
> +		if (!net_eq(dev_net(vxlan->dev), net))
>  			unregister_netdevice_queue(vxlan->dev, head);
> -		}
>  	}
> 
>  	for (h = 0; h < PORT_HASH_SIZE; ++h)

Looks good to me, you can keep my Reviewed-by: tag for v3. Thanks!

-- 
Stefano