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Date: Mon, 28 Mar 2022 15:49:06 +0200
From: Florian Westphal <fw@strlen.de>
To: Geliang Tang <geliang.tang@suse.com>
Cc: Florian Westphal <fw@strlen.de>, mptcp@lists.linux.dev
Subject: Re: [PATCH mptcp-next v7 1/8] mptcp: add struct mptcp_sched_ops
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References: <cover.1648459865.git.geliang.tang@suse.com>
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Geliang Tang <geliang.tang@suse.com> wrote:
> > > +	if (!sched->get_subflow)
> > > +		return -EINVAL;
> > > +
> > > +	if (mptcp_sched_find(net, sched->name))
> > > +		return -EEXIST;
> > > +
> > > +	spin_lock(&pernet->lock);
> > > +	list_add_tail_rcu(&sched->list, &pernet->sched_list);
> > > +	spin_unlock(&pernet->lock);
> > 
> > This is racy.  Lock, test, add, unlock, not test, lock, ...
> 
> How should I fix this?

spin_lock(&pernet->lock);
if (mptcp_sched_find(net, sched->name)) {
	spin_unlock(&pernet->lock);
	return -EEXIST;
}
list_add_....