rcu: Settle config for userspace extended quiescent state

Create a new config option under the RCU menu that put
CPUs under RCU extended quiescent state (as in dynticks
idle mode) when they run in userspace. This require
some contribution from architectures to hook into kernel
and userspace boundaries.

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>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index 72f2fa189cc5..1401a7587973 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -281,4 +281,14 @@ config SECCOMP_FILTER
 
           See Documentation/prctl/seccomp_filter.txt for details.
 
+config HAVE_RCU_USER_QS
+        bool
+        help
+          Provide kernel entry/exit hooks necessary for userspace
+          RCU extended quiescent state. Syscalls need to be wrapped inside
+          rcu_user_exit()-rcu_user_enter() through the slow path using
+          TIF_NOHZ flag. Exceptions handlers must be wrapped as well. Irqs
+          are already protected inside rcu_irq_enter/rcu_irq_exit() but
+          preemption or signal handling on irq exit still need to be protected.
+
 source "kernel/gcov/Kconfig"