linux-kernel - Re: [PATCH 6/6] x86: Exit RCU extended QS on notify resume

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Message-ID: <20120709174321.GC8185@somewhere.redhat.com>
Date:	Mon, 9 Jul 2012 19:43:23 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Josh Triplett <josh@...htriplett.org>,
	Kevin Hilman <khilman@...com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephen Hemminger <shemminger@...tta.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sven-Thorsten Dietrich <thebigcorporation@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 6/6] x86: Exit RCU extended QS on notify resume

On Fri, Jul 06, 2012 at 09:33:38AM -0700, Paul E. McKenney wrote:
> On Fri, Jul 06, 2012 at 02:00:18PM +0200, Frederic Weisbecker wrote:
> > do_notify_resume() may be called on irq exit but it won't
> > be protected between rcu_irq_enter() and rcu_irq_exit()
> > and we don't call rcu_user_exit() on irq entry (unlike
> > syscalls/exceptions entry).
> > 
> > Since it can use RCU read side critical section, we must call
> > rcu_user_exit() before doing anything there.
> > 
> > This complete support for RCU userspace extended quiescent state
> > in x86.
> > 
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > Cc: Alessio Igor Bogani <abogani@...nel.org>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Avi Kivity <avi@...hat.com>
> > Cc: Chris Metcalf <cmetcalf@...era.com>
> > Cc: Christoph Lameter <cl@...ux.com>
> > Cc: Geoff Levand <geoff@...radead.org>
> > Cc: Gilad Ben Yossef <gilad@...yossef.com>
> > Cc: Hakan Akkan <hakanakkan@...il.com>
> > Cc: H. Peter Anvin <hpa@...or.com>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Josh Triplett <josh@...htriplett.org>
> > Cc: Kevin Hilman <khilman@...com>
> > Cc: Max Krasnyansky <maxk@...lcomm.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Stephen Hemminger <shemminger@...tta.com>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Sven-Thorsten Dietrich <thebigcorporation@...il.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  arch/x86/Kconfig         |    1 +
> >  arch/x86/kernel/signal.c |    2 ++
> >  2 files changed, 3 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index c70684f..38dfcc2 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -95,6 +95,7 @@ config X86
> >  	select KTIME_SCALAR if X86_32
> >  	select GENERIC_STRNCPY_FROM_USER
> >  	select GENERIC_STRNLEN_USER
> > +	select HAVE_RCU_USER_QS if X86_64
> 
> And I will bite yet again.  Why only 64-bit kernels?
> 
> 							Thanx, Paul

Because I don't want to spend time on implementing it the same way on 32
in case people disagree with the whole design :)
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