Re: [PATCH v2] vxlan: remove the redundant gro_cells_destroy() calling.

[Zhiqiang Liu <liuzhiqiang26@huawei.com>]

> On Sat, 16 Mar 2019 13:24:39 +0800
> Zhiqiang Liu <liuzhiqiang26@huawei.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@huawei.com>
>> Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
>> Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
>> Reviewed-by: Zhiqiang Liu <liuzhiqiang26@huawei.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!
> 

Thank you for your patience to reply. And thanks for Eric and David Miller again.
I will make the v3 as your suggestion.