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

[Josh Triplett]

On Thu, Aug 30, 2012 at 02:05:30PM -0700, Paul E. McKenney wrote:
> From: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> 
> 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@xxxxxxxxx>
> Cc: Alessio Igor Bogani <abogani@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Avi Kivity <avi@xxxxxxxxxx>
> Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Geoff Levand <geoff@xxxxxxxxxxxxx>
> Cc: Gilad Ben Yossef <gilad@xxxxxxxxxxxxx>
> Cc: Hakan Akkan <hakanakkan@xxxxxxxxx>
> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> Cc: Kevin Hilman <khilman@xxxxxx>
> Cc: Max Krasnyansky <maxk@xxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Stephen Hemminger <shemminger@xxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Sven-Thorsten Dietrich <thebigcorporation@xxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>

>  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
> 
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