Re: [PATCH tip/core/rcu 13/26] x86: Exit RCU extended QS on notify resume

Josh Triplett
2012-08-31T23:54:23Z

On Thu, Aug 30, 2012 at 02:05:30PM -0700, Paul E. McKenney wrote:
> From: Frederic Weisbecker <fweisbec@gmail.com>
>
> do_notify_resume() may be called on irq or exception
> exit. But at that time the exception has already called
> rcu_user_enter() and the irq has already called rcu_irq_exit().
>
> Since it can use RCU read side critical section, we must call
> rcu_user_exit() before doing anything there. Then we must call
> back rcu_user_enter() after this function because we know we are
> going to userspace from there.
>
> This complete support for userspace RCU extended quiescent state
> in x86-64.
>
> 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>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

> arch/x86/Kconfig | 1 +
> arch/x86/kernel/signal.c | 4 ++++
> 2 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index ba2657c..5cd953a 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -97,6 +97,7 @@ 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
>
> config INSTRUCTION_DECODER
> def_bool (KPROBES || PERF_EVENTS || UPROBES)
> diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
> index b280908..bca0ab9 100644
> --- a/arch/x86/kernel/signal.c
> +++ b/arch/x86/kernel/signal.c
> @@ -779,6 +779,8 @@ 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)
> @@ -804,6 +806,8 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
> #ifdef CONFIG_X86_32
> clear_thread_flag(TIF_IRET);
> #endif /* CONFIG_X86_32 */
> +
> + rcu_user_enter();
> }
>
> void signal_fault(struct pt_regs *regs, void __user *frame, char *where)
> --
> 1.7.8
>