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Message-ID: <20190717000757.GQ14271@linux.ibm.com>
Date: Tue, 16 Jul 2019 17:07:57 -0700
From: "Paul E. McKenney" <paulmck@...ux.ibm.com>
To: Joel Fernandes <joel@...lfernandes.org>
Cc: linux-kernel@...r.kernel.org, Alexey Kuznetsov <kuznet@....inr.ac.ru>,
Bjorn Helgaas <bhelgaas@...gle.com>, Borislav Petkov <bp@...en8.de>,
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"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
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"Rafael J. Wysocki" <rjw@...ysocki.net>,
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Steven Rostedt <rostedt@...dmis.org>, Tejun Heo <tj@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>, will@...nel.org,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH 2/9] rcu: Add support for consolidated-RCU reader
checking (v3)
On Tue, Jul 16, 2019 at 06:02:05PM -0400, Joel Fernandes wrote:
> On Tue, Jul 16, 2019 at 11:53:03AM -0700, Paul E. McKenney wrote:
> [snip]
> > > > A few more things below.
> > > > > ---
> > > > > include/linux/rculist.h | 28 ++++++++++++++++++++-----
> > > > > include/linux/rcupdate.h | 7 +++++++
> > > > > kernel/rcu/Kconfig.debug | 11 ++++++++++
> > > > > kernel/rcu/update.c | 44 ++++++++++++++++++++++++----------------
> > > > > 4 files changed, 67 insertions(+), 23 deletions(-)
> > > > >
> > > > > diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> > > > > index e91ec9ddcd30..1048160625bb 100644
> > > > > --- a/include/linux/rculist.h
> > > > > +++ b/include/linux/rculist.h
> > > > > @@ -40,6 +40,20 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
> > > > > */
> > > > > #define list_next_rcu(list) (*((struct list_head __rcu **)(&(list)->next)))
> > > > >
> > > > > +/*
> > > > > + * Check during list traversal that we are within an RCU reader
> > > > > + */
> > > > > +
> > > > > +#ifdef CONFIG_PROVE_RCU_LIST
> > > >
> > > > This new Kconfig option is OK temporarily, but unless there is reason to
> > > > fear malfunction that a few weeks of rcutorture, 0day, and -next won't
> > > > find, it would be better to just use CONFIG_PROVE_RCU. The overall goal
> > > > is to reduce the number of RCU knobs rather than grow them, must though
> > > > history might lead one to believe otherwise. :-/
> > >
> > > If you want, we can try to drop this option and just use PROVE_RCU however I
> > > must say there may be several warnings that need to be fixed in a short
> > > period of time (even a few weeks may be too short) considering the 1000+
> > > uses of RCU lists.
> > Do many people other than me build with CONFIG_PROVE_RCU? If so, then
> > that would be a good reason for a temporary CONFIG_PROVE_RCU_LIST,
> > as in going away in a release or two once the warnings get fixed.
>
> PROVE_RCU is enabled by default with PROVE_LOCKING, so it is used quite
> heavilty.
>
> > > But I don't mind dropping it and it may just accelerate the fixing up of all
> > > callers.
> >
> > I will let you decide based on the above question. But if you have
> > CONFIG_PROVE_RCU_LIST, as noted below, it needs to depend on RCU_EXPERT.
>
> Ok, will make it depend. But yes for temporary purpose, I will leave it as a
> config and remove it later.
Very good, thank you! Plus you got another ack. ;-)
Thanx, Paul
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