linux-kernel - Re: linux-next: manual merge of the rcu tree with the tip tree

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Message-ID: <20170801141548.mivo7du4nl26r7z3@hirez.programming.kicks-ass.net>
Date:   Tue, 1 Aug 2017 16:15:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: manual merge of the rcu tree with the tip tree

On Tue, Aug 01, 2017 at 03:58:49PM +0200, Peter Zijlstra wrote:
> On Tue, Aug 01, 2017 at 06:43:14AM -0700, Andy Lutomirski wrote:
> > Anyway, can you document whatever property you require with a comment
> > in switch_mm() or wherever you're finding that property so that future
> > arch changes don't break it?
> 
> We need _a_ smp_mb after rq->curr store. x86 has plenty.

That is, we need it when we change to a different !0 mm. And we have the
mm_cpumask() atomics at the very least, even if loading a new CR3 would
not be serializing.