netdev - Re: [PATCH net-next v5] rtnetlink: Support fine-grained netdevice bulk deletion

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Date:   Tue, 4 Jan 2022 10:21:21 +0200
From:   Lahav Schlesinger <lschlesinger@...venets.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     David Ahern <dsahern@...il.com>, netdev@...r.kernel.org,
        nikolay@...dia.com
Subject: Re: [PATCH net-next v5] rtnetlink: Support fine-grained netdevice
 bulk deletion

On Wed, Dec 08, 2021 at 04:45:44PM -0800, Jakub Kicinski wrote:
> CAUTION: External E-Mail - Use caution with links and attachments
>
>
> On Wed, 8 Dec 2021 17:18:48 -0700 David Ahern wrote:
> > On 12/8/21 5:04 PM, Jakub Kicinski wrote:
> > >> I think marking the dev's and then using a delete loop is going to be
> > >> the better approach - avoid the sort and duplicate problem. I use that
> > >> approach for nexthop deletes:
> > >>
> > >> https://urldefense.proofpoint.com/v2/url?u=https-3A__git.kernel.org_pub_scm_linux_kernel_git_netdev_net-2Dnext.git_tree_net_ipv4_nexthop.c-23n1849&d=DwICAg&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=-WbGKi6-8WU3IfnrkySymtcZWJMn_aVdolIPebPZGu4&m=td9sv1_NnALM3QjLFg8h9u1P7DUJJL2YhzqyneZ95Gc&s=nEGgvxCwd3MrSXWhv-5Fo7mUlBkuKbHRBAO4VO9mG2o&e=
> > >>
> > >> Find a hole in net_device struct in an area used only for control path
> > >> and add 'bool grp_delete' (or a 1-bit hole). Mark the devices on pass
> > >> and delete them on another.
> > >
> > > If we want to keep state in the netdev itself we can probably piggy
> > > back on dev->unreg_list. It should be initialized to empty and not
> > > touched unless device goes thru unregister.
> >
> > isn't that used when the delink function calls unregister_netdevice_queue?
>
> Sure but all the validation is before we start calling delink, so
> doesn't matter?
>
> list to_kill, queued;
>
> for_each_attr(nest) {
>         ...
>
>         dev = get_by_index(nla_get_s32(..));
>         if (!dev)
>                 goto cleanup;
>         if (!list_empty(&dev->unreg_list))
>                 goto cleanup;
>         ...
>
>         list_add(&to_kill, &dev->unreg_list);
> }
>
> for_each_entry_safe(to_kill) {
>         list_del_init(&dev->unreg_list);
>         ->dellink(dev, queued);
> }
>
> unreg_many(queued);
>
> return
>
> cleanup:
>         for_each_entry_safe(to_kill) {
>                 list_del_init(&dev->unreg_list);
>         }
>
> No?

Hi Jakub, I just sent a V6 for this patch. Just wanted to note that I
tried this approach of using unreg_list, but it caused issues with e.g.
veth deletion - the dellink() of a veth peer automatically adds the
other peer to the queued list. So if the list of ifindices contains
both peers then when 'to_kill' is iterated, both the current device
and the next pointer will have their 'unreg_list' moved to the other
list, which later raised a page fault when 'to_kill' was further
iterated upon.

Therefore instead I added a big flag in a "hole" inside struct
net_device, as David suggested.