netdev - Re: [PATCH net-next] ipv6: Do not use this_cpu

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Message-ID: <1507487115.14419.31.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Sun, 08 Oct 2017 11:25:15 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     Ido Schimmel <idosch@...lanox.com>, netdev@...r.kernel.org,
        davem@...emloft.net, weiwan@...gle.com, mlxsw@...lanox.com
Subject: Re: [PATCH net-next] ipv6: Do not use this_cpu_ptr() in preemptible
 context

On Sun, 2017-10-08 at 19:54 +0300, Ido Schimmel wrote:
> Hi Eric,

> >  	prev = cmpxchg(p, NULL, pcpu_rt);
> > -	if (prev) {
> > -		/* If someone did it before us, return prev instead */
> > -		/* release refcnt taken by ip6_rt_pcpu_alloc() */
> > -		dst_release_immediate(&pcpu_rt->dst);
> > -		/* release refcnt taken by above dst_hold() */
> > -		dst_release_immediate(&pcpu_rt->dst);
> > -		dst_hold(&prev->dst);
> > -		pcpu_rt = prev;
> > -	}
> > +	BUG_ON(prev);
> 
> Is this BUG_ON() now valid because of the local_bh_disable() in
> ip6_pol_route()?

Yes, this bug to trigger would need this code be re-entered from a hard
IRQ, and that would be wrong of course.