ACK: [SRU][Bionic][PATCH 1/1] xfrm: reuse uncached_list to track xdsts

[Seth Forshee]

On Fri, Apr 20, 2018 at 12:14:10PM -0400, Joseph Salisbury wrote:
> From: Xin Long <lucien.xin at gmail.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1746474
> 
> In early time, when freeing a xdst, it would be inserted into
> dst_garbage.list first. Then if it's refcnt was still held
> somewhere, later it would be put into dst_busy_list in
> dst_gc_task().
> 
> When one dev was being unregistered, the dev of these dsts in
> dst_busy_list would be set with loopback_dev and put this dev.
> So that this dev's removal wouldn't get blocked, and avoid the
> kmsg warning:
> 
>   kernel:unregister_netdevice: waiting for veth0 to become \
>   free. Usage count = 2
> 
> However after Commit 52df157f17e5 ("xfrm: take refcnt of dst
> when creating struct xfrm_dst bundle"), the xdst will not be
> freed with dst gc, and this warning happens.
> 
> To fix it, we need to find these xdsts that are still held by
> others when removing the dev, and free xdst's dev and set it
> with loopback_dev.
> 
> But unfortunately after flow_cache for xfrm was deleted, no
> list tracks them anymore. So we need to save these xdsts
> somewhere to release the xdst's dev later.
> 
> To make this easier, this patch is to reuse uncached_list to
> track xdsts, so that the dev refcnt can be released in the
> event NETDEV_UNREGISTER process of fib_netdev_notifier.
> 
> Thanks to Florian, we could move forward this fix quickly.
> 
> Fixes: 52df157f17e5 ("xfrm: take refcnt of dst when creating struct xfrm_dst bundle")
> Reported-by: Jianlin Shi <jishi at redhat.com>
> Reported-by: Hangbin Liu <liuhangbin at gmail.com>
> Tested-by: Eyal Birger <eyal.birger at gmail.com>
> Signed-off-by: Xin Long <lucien.xin at gmail.com>
> Signed-off-by: Steffen Klassert <steffen.klassert at secunet.com>
> (cherry picked from commit 510c321b557121861601f9d259aadd65aa274f35)
> Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>

Clean cherry pick, positive testing.

Acked-by: Seth Forshee <seth.forshee at canonical.com>