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

[Frederic Weisbecker <fweisbec@gmail.com>]

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@gmail.com>
> > Cc: Alessio Igor Bogani <abogani@kernel.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Avi Kivity <avi@redhat.com>
> > Cc: Chris Metcalf <cmetcalf@tilera.com>
> > Cc: Christoph Lameter <cl@linux.com>
> > Cc: Geoff Levand <geoff@infradead.org>
> > Cc: Gilad Ben Yossef <gilad@benyossef.com>
> > Cc: Hakan Akkan <hakanakkan@gmail.com>
> > Cc: H. Peter Anvin <hpa@zytor.com>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Josh Triplett <josh@joshtriplett.org>
> > Cc: Kevin Hilman <khilman@ti.com>
> > Cc: Max Krasnyansky <maxk@qualcomm.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Stephen Hemminger <shemminger@vyatta.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
> > Cc: Thomas Gleixner <tglx@linutronix.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 :)