linux-kernel - Re: [PATCH tip/core/rcu 2/4] docs: Update RCU's hotplug requirements with a bit about design

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Date:   Tue, 10 Nov 2020 15:33:28 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, rostedt@...dmis.org, dhowells@...hat.com,
        edumazet@...gle.com, fweisbec@...il.com, oleg@...hat.com
Subject: Re: [PATCH tip/core/rcu 2/4] docs: Update RCU's hotplug requirements
 with a bit about design

On Mon, Nov 09, 2020 at 06:14:33PM +0100, Peter Zijlstra wrote:
> On Mon, Nov 09, 2020 at 08:24:52AM -0800, Paul E. McKenney wrote:
> > On Mon, Nov 09, 2020 at 01:23:17PM +0100, Peter Zijlstra wrote:
> > > On Thu, Nov 05, 2020 at 03:05:08PM -0800, paulmck@...nel.org wrote:
> > > > From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
> > > > 
> > > > The rcu_barrier() section of the "Hotplug CPU" section discusses
> > > > deadlocks, however the description of deadlocks other than those involving
> > > > rcu_barrier() is rather incomplete.
> > > > 
> > > > This commit therefore continues the section by describing how RCU's
> > > > design handles CPU hotplug in a deadlock-free way.
> > > > 
> > > > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > > > Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> > > > ---
> > > >  .../RCU/Design/Requirements/Requirements.rst       | 49 +++++++++++++++++-----
> > > >  1 file changed, 39 insertions(+), 10 deletions(-)
> > > > 
> > > > diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
> > > > index 1ae79a1..98557fe 100644
> > > > --- a/Documentation/RCU/Design/Requirements/Requirements.rst
> > > > +++ b/Documentation/RCU/Design/Requirements/Requirements.rst
> > > > @@ -1929,16 +1929,45 @@ The Linux-kernel CPU-hotplug implementation has notifiers that are used
> > > >  to allow the various kernel subsystems (including RCU) to respond
> > > >  appropriately to a given CPU-hotplug operation. Most RCU operations may
> > > >  be invoked from CPU-hotplug notifiers, including even synchronous
> > > > -grace-period operations such as ``synchronize_rcu()`` and
> > > > -``synchronize_rcu_expedited()``.
> > > 
> > > I was under the impression that this rst crap now recognises func() and
> > > you no longer need to make the text unreadable with "``".
> > 
> > It was there to start with, but good point.  How about the commit
> > below?
> 
> Much appreciated, thanks!

Thanks for making the change, I built it and it looks good in my web browser
;-).

BTW, these APIs are obsolete due to consolidation. Paul could you remove them
from the document?:
 synchronize_rcu_bh(), synchronize_rcu_bh_expedited(), call_rcu_bh(),
 rcu_barrier_bh().

thanks!

-Joel