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

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

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

>  config INSTRUCTION_DECODER
>  	def_bool (KPROBES || PERF_EVENTS || UPROBES)
> diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
> index 21af737..5af078e 100644
> --- a/arch/x86/kernel/signal.c
> +++ b/arch/x86/kernel/signal.c
> @@ -776,6 +776,8 @@ static void do_signal(struct pt_regs *regs)
>  void
>  do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
>  {
> +	rcu_user_exit();
> +
>  #ifdef CONFIG_X86_MCE
>  	/* notify userspace of pending MCEs */
>  	if (thread_info_flags & _TIF_MCE_NOTIFY)
> -- 
> 1.7.5.4
>