linux-kernel - Re: [PATCH V2 2/7] rcu: cleanup rcu_preempt_deferred

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Message-ID: <20200218164314.GG2935@paulmck-ThinkPad-P72>
Date:   Tue, 18 Feb 2020 08:43:14 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH V2 2/7] rcu: cleanup rcu_preempt_deferred_qs()

On Tue, Feb 18, 2020 at 09:41:24AM -0500, Steven Rostedt wrote:
> On Mon, 17 Feb 2020 15:23:07 -0800
> "Paul E. McKenney" <paulmck@...nel.org> wrote:
> 
> > > I'm still asking for more comments.
> > > 
> > > By now, I have received some precious comments, mainly due to my
> > > stupid naming mistakes and a misleading changelog. I should have
> 
> How about typos?

We appear to have enough typos, thank you!

> > > updated all these with a new series patches. But I hope I
> > > can polish more in the new patchset with more suggestions from
> > > valuable comments, especially in x86,scheduler,percpu and rcu
> > > areas.
> > > 
> > > I'm very obliged to hear anything.  
> > 
> > commit 23a58acde0eea57ac77377e5d50d9562b2dbdfaa
> > Author: Lai Jiangshan <laijs@...ux.alibaba.com>
> > Date:   Sat Feb 15 14:37:26 2020 -0800
> > 
> >     rcu: Don't set nesting depth negative in rcu_preempt_deferred_qs()
> >     
> >     Now that RCU flavors have been consolidated, an RCU-preempt
> >     rcu_rea_unlock() in an interrupt or softirq handler cannot possibly
> 
> What's a "rea"? ;-)

A typo.  Probably mine.  Thank you for catching it, will fix!  ;-)

But maybe an rcu_rhea_lock()?  Just in case the rheas are getting loose?

							Thanx, Paul

> -- Steve
> 
> >     end the RCU read-side critical section.  Consider the old vulnerability
> >     involving rcu_preempt_deferred_qs() being invoked within such a handler
> >     that interrupted an extended RCU read-side critical section, in which
> >     a wakeup might be invoked with a scheduler lock held.  Because
> >     rcu_read_unlock_special() no longer does wakeups in such situations,
> >     it is no longer necessary for rcu_preempt_deferred_qs() to set the
> >     nesting level negative.
> >     
> >     This commit therfore removes this recursion-protection code from
> >     rcu_preempt_deferred_qs().
> >     
> >     Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
> >     Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> > 
> >