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

Josh Triplett
2012-08-31T23:52:36Z

On Thu, Aug 30, 2012 at 02:05:28PM -0700, Paul E. McKenney wrote:
> From: Frederic Weisbecker <fweisbec@gmail.com>
>
> 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@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>

> 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
>