linux-kernel - Re: rcu: Merge RCU-bh into RCU-preempt

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Message-Id: <20181108164247.GL4170@linux.ibm.com>
Date:   Thu, 8 Nov 2018 08:42:47 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     tglx@...utronix.de, linux-rt-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: rcu: Merge RCU-bh into RCU-preempt

On Thu, Nov 08, 2018 at 05:02:57PM +0100, Sebastian Andrzej Siewior wrote:
> On 2018-11-01 16:18:04 [-0700], Paul E. McKenney wrote:
> > The need for this goes away as of the current merge window because
> > RCU-bh has gone away.  (Aside from still being able to do things
> > like rcu_read_lock_bh() as a documentation device.)
> 
> So in -RT rcu_read_lock_bh() does
>  { local_bh_disable() ;  rcu_read_lock() }
> 
> So you are saying that this is also the case in v4.20?

No, rcu_read_lock_bh() and rcu_read_unlock_bh() are unchanged in v4.20.
With the new RCU grace-period mechanism, local_bh_disable() blocks future
grace periods on its own.

Unless I am missing something (quite probable, actually), the v4.20
definitions of rcu_read_lock_bh() and rcu_read_unlock_bh() should work
as-is for -rt.

							Thanx, Paul