linux-kernel - Re: [PATCH RFC tip/core/rcu] SRCU rewrite

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Message-ID: <20161115145536.GE11311@worktop.programming.kicks-ass.net>
Date:   Tue, 15 Nov 2016 15:55:36 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        dipankar <dipankar@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Triplett <josh@...htriplett.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        rostedt <rostedt@...dmis.org>,
        David Howells <dhowells@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        dvhart <dvhart@...ux.intel.com>, fweisbec <fweisbec@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        bobby prani <bobby.prani@...il.com>, ldr709 <ldr709@...il.com>
Subject: Re: [PATCH RFC tip/core/rcu] SRCU rewrite

On Tue, Nov 15, 2016 at 06:26:27AM -0800, Paul E. McKenney wrote:
> On Tue, Nov 15, 2016 at 02:59:12PM +0100, Peter Zijlstra wrote:

> > The smp_mb()s in read_{un,}lock() and the lock in call_srcu() come to
> > mind.
> 
> There is some possibility of weakening the srcu_read_unlock() ordering,
> but one step at a time.
> 
> Has the lock in call_srcu() been causing trouble?  Easy to fix if so,
> but as you noted in another email today, we don't need complexity for
> complexity's sake.  And no reports of problems with this have reached
> me thus far.

It was a cause for concern in the optimistic fault series, but since
that never got sorted, it hasn't shown up in practise afaik.