linux-kernel - Re: [PATCH 0/5] srcu fixes

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Message-ID: <811d08e3-efb8-4398-8fbc-6b5d030afb15@paulmck-laptop>
Date:   Tue, 3 Oct 2023 20:30:45 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Yong He <zhuangel570@...il.com>,
        Neeraj upadhyay <neeraj.iitr10@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Uladzislau Rezki <urezki@...il.com>, RCU <rcu@...r.kernel.org>
Subject: Re: [PATCH 0/5] srcu fixes

On Tue, Oct 03, 2023 at 08:21:42PM -0700, Paul E. McKenney wrote:
> On Tue, Oct 03, 2023 at 05:35:31PM -0700, Paul E. McKenney wrote:
> > On Wed, Oct 04, 2023 at 01:28:58AM +0200, Frederic Weisbecker wrote:
> > > Hi,
> > > 
> > > This contains a fix for "SRCU: kworker hung in synchronize_srcu":
> > > 
> > > 	http://lore.kernel.org/CANZk6aR+CqZaqmMWrC2eRRPY12qAZnDZLwLnHZbNi=xXMB401g@mail.gmail.com
> > > 
> > > And a few cleanups.
> > > 
> > > Passed 50 hours of SRCU-P and SRCU-N.
> > > 
> > > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> > > 	srcu/fixes
> > > 
> > > HEAD: 7ea5adc5673b42ef06e811dca75e43d558cc87e0
> > > 
> > > Thanks,
> > > 	Frederic
> > 
> > Very good, and a big "Thank You!!!" to all of you!
> > 
> > I queued this series for testing purposes, and have started a bunch of
> > SRCU-P and SRCU-N tests on one set of systems, and a single SRCU-P and
> > SRCU-N on another system, but with both scenarios resized to 40 CPU each.

The 200*1h of SRCU-N and the 100*1h of SRCU-p passed other than the usual
tick-stop errors.  (Is there a patch for that one?)  The 40-CPU SRCU-N
run was fine, but the 40-CPU SRCU-P run failed due to the fanouts setting
a maximum of 16 CPUs.  So I started a 10-hour 40-CPU SRCU-P and a pair
of 10-hour 16-CPU SRCU-N runs on one system, and 200*10h of SRCU-N and
100*10h of SRCU-P.

I will let you know how it goes.

							Thanx, Paul

> > While that is in flight, a few questions:
> > 
> > o	Please check the Co-developed-by rules.  Last I knew, it was
> > 	necessary to have a Signed-off-by after each Co-developed-by.
> > 
> > o	Is it possible to get a Tested-by from the original reporter?
> > 	Or is this not reproducible?
> > 
> > o	Is it possible to convince rcutorture to find this sort of
> > 	bug?  Seems like it should be, but easy to say...
> 
> And one other thing...
> 
> o	What other bugs like this one are hiding elsewhere
> 	in RCU?
> 
> > o	Frederic, would you like to include this in your upcoming
> > 	pull request?  Or does it need more time?
> 
> 						Thanx, Paul
> 
> > > ---
> > > 
> > > Frederic Weisbecker (5):
> > >       srcu: Fix callbacks acceleration mishandling
> > >       srcu: Only accelerate on enqueue time
> > >       srcu: Remove superfluous callbacks advancing from srcu_start_gp()
> > >       srcu: No need to advance/accelerate if no callback enqueued
> > >       srcu: Explain why callbacks invocations can't run concurrently
> > > 
> > > 
> > >  kernel/rcu/srcutree.c | 55 ++++++++++++++++++++++++++++++++++++---------------
> > >  1 file changed, 39 insertions(+), 16 deletions(-)