rcu: Exit RCU extended QS on user preemption

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>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0bd599ba9d91064bdd63d0cfe5b5afad8e1d5753..e841dfc1a5ab00bdbbd83d8f204fd60d74741cb6 100644 (file)
--- 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
  *