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

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Date:	Fri, 6 Jul 2012 09:33:38 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.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 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

>  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
> 

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