Re: [PATCH tip/core/rcu 11/26] rcu: Exit RCU extended QS on userpreemption

[Josh Triplett]

On Thu, Aug 30, 2012 at 02:05:28PM -0700, Paul E. McKenney wrote:
> From: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> 
> When exceptions or irq are about to resume userspace, if
> the task needs to be rescheduled, the arch low level code
> calls schedule() directly.
> 
> At that time we may be in extended quiescent state from RCU
> POV: the exception is not anymore protected inside
> rcu_user_exit() - rcu_user_enter() and the irq has called
> rcu_irq_exit() already.
> 
> Create a new API schedule_user() that calls schedule() inside
> rcu_user_exit()-rcu_user_enter() in order to protect it. Archs
> will need to rely on it now to implement user preemption safely.
> 
> 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>

>  kernel/sched/core.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0bd599b..e841dfc 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3463,6 +3463,13 @@ asmlinkage void __sched schedule(void)
>  }
>  EXPORT_SYMBOL(schedule);
>  
> +asmlinkage void __sched schedule_user(void)
> +{
> +	rcu_user_exit();
> +	schedule();
> +	rcu_user_enter();
> +}
> +
>  /**
>   * schedule_preempt_disabled - called with preemption disabled
>   *
> -- 
> 1.7.8
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/