Re: [PATCH RESEND mptcp-next v5 1/8] mptcp: add struct mptcp_sched_ops

[Florian Westphal <fw@strlen.de>]

Geliang Tang <geliang.tang@suse.com> wrote:
> On Thu, Mar 24, 2022 at 04:03:27PM +0100, Florian Westphal wrote:
> > Geliang Tang <geliang.tang@suse.com> wrote:
> > > On Thu, Mar 24, 2022 at 03:27:53PM +0100, Florian Westphal wrote:
> > > > Geliang Tang <geliang.tang@suse.com> wrote:
> > > > > This patch added struct mptcp_sched_ops. And define the scheduler
> > > > > register, unregister and find functions.
> > > > 
> > > > ... but why are they pernet?  Makes no sense to me, so an
> > > > explanation would help.  Or, remove the pernet ops.
> > > > 
> > > > All callers pass &init_net, so I don't think there is any reason
> > > > for pernet data structures here.
> > > 
> > > v4 used global list instead of pernet list:
> > > 
> > > https://patchwork.kernel.org/project/mptcp/patch/02c1d2d2eee134713737fe5c5f73127e8c741589.1647942374.git.geliang.tang@suse.com/
> 
> Florian, should I remove synchronize_rcu() in v4 too?

I think so.  Else you need to add a comment as to why its needed.

I suspect full 'rmmod mptcp_sched_example' sequence would be:

1. mptcp_unregister_scheduler(&example_sched);
2. walk all active mptcp sockets to re-set their scheduler
in case something still uses 'example_sched'
3. complete the rmmod

In that case, we might need a synchronize_rcu after 2), but
not 1.