[PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace periods

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

Hello!

This series, possibly for v3.21, contains changes that allow in-kernel
code to specify that all subsequent synchronous grace-period primitives
(synchronize_rcu() and friends) be expedited.  New rcu_expedite_gp()
and rcu_unexpedite_gp() primitives enable and disable expediting,
and these may be nested.  Note that the rcu_expedited boot/sysfs
variable, if non-zero, causes expediting to happen regardless of calls
to rcu_expedite_gp().

Because one of the use cases for these primitives is to expedite
grace periods during the in-kernel portion of boot, a new Kconfig
parameter named CONFIG_RCU_EXPEDITE_BOOT causes the kernel to act
as if rcu_expedite_gp() was called very early in boot.  At the end
of boot (presumably just before init is spawned), a call to
rcu_end_inkernel_boot() will provide the matching rcu_unexpedite_gp()
if required.

The patches in this series are as follows:

1.	Add rcu_expedite_gp() and rcu_unexpedite_gp() functions.

2.	Add rcutorture tests for rcu_expedite_gp() and rcu_unexpedite_gp().

3.	Change open-coded access to the rcu_expedited variable to
	instead use a new rcu_gp_is_expedited() function.

4.	Add the CONFIG_RCU_EXPEDITE_BOOT Kconfig parameter and
	the rcu_end_inkernel_boot() function.

This passes light rcutorture testing.

							Thanx, Paul

------------------------------------------------------------------------

 b/include/linux/rcupdate.h |   21 ++++++++++++++++
 b/init/Kconfig             |   13 +++++++++
 b/kernel/rcu/rcutorture.c  |   24 ++++++++++++++++++
 b/kernel/rcu/srcu.c        |    2 -
 b/kernel/rcu/tree.c        |    9 +++---
 b/kernel/rcu/tree_plugin.h |    2 -
 b/kernel/rcu/update.c      |   59 ++++++++++++++++++++++++++++++++++++++++++++-
 7 files changed, 123 insertions(+), 7 deletions(-)