Once srcu_init() is called, the SRCU core will make use of delayed
workqueues, which rely on timers.  However init_timers() is called
several steps after rcu_init().  This means that a call_srcu() after
rcu_init() but before init_timers() would find itself within a dangerously
uninitialized timer core.

This commit therefore creates a separate call to srcu_init() after
init_timer() completes, which ensures that we stay in early SRCU mode
until timers are safe(r).

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

There is a need for a non-blocking polling interface for RCU grace
periods, so this commit supplies start_poll_synchronize_rcu() and
poll_state_synchronize_rcu() for this purpose.  Note that the existing
get_state_synchronize_rcu() may be used if future grace periods are
inevitable (perhaps due to a later call_rcu() invocation).  The new
start_poll_synchronize_rcu() is to be used if future grace periods
might not otherwise happen.  Finally, poll_state_synchronize_rcu()
provides a lockless check for a grace period having elapsed since
the corresponding call to either of the get_state_synchronize_rcu()
or start_poll_synchronize_rcu().

As with get_state_synchronize_rcu(), the return value from either
get_state_synchronize_rcu() or start_poll_synchronize_rcu() is passed in
to a later call to either poll_state_synchronize_rcu() or the existing
(might_sleep) cond_synchronize_rcu().

[ paulmck: Revert cond_synchronize_rcu() to might_sleep() per Frederic Weisbecker feedback. ]
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The following changes are introduced:

1. Rename rcu_invoke_kfree_callback() to rcu_invoke_kvfree_callback(),
as well as the associated trace events, so the rcu_kfree_callback(),
becomes rcu_kvfree_callback(). The reason is to be aligned with kvfree()
notation.

2. Rename __is_kfree_rcu_offset to __is_kvfree_rcu_offset. All RCU
paths use kvfree() now instead of kfree(), thus rename it.

3. Rename kfree_call_rcu() to the kvfree_call_rcu(). The reason is,
it is capable of freeing vmalloc() memory now. Do the same with
__kfree_rcu() macro, it becomes __kvfree_rcu(), the goal is the
same.

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Co-developed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Replace kfree() with kvfree() in rcu_reclaim_tiny().
This makes it possible to release either SLAB or vmalloc
objects after a GP.

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit removes kfree_rcu() special-casing and the lazy-callback
handling from Tree RCU.  It moves some of this special casing to Tiny RCU,
the removal of which will be the subject of later commits.

This results in a nice negative delta.

Suggested-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Add slab.h #include, thanks to kbuild test robot <lkp@intel.com>. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The rcu_qs is disabling IRQs by self so no need to do the same in raise_softirq
but instead we can save some cycles using raise_softirq_irqoff directly.

CC: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

doc.2019.01.26a:  Documentation updates.
fixes.2019.01.26a:  Miscellaneous fixes.
sil.2019.01.26a:  Removal of a few more spin_is_locked() instances.
spdx.2019.02.09a:  Add SPDX identifiers to RCU files
srcu.2019.01.26a:  SRCU updates.
torture.2019.01.26a: Torture-test updates.

Replace the license boiler plate with a SPDX license identifier.
While in the area, update an email address.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

The name rcu_check_callbacks() arguably made sense back in the early
2000s when RCU was quite a bit simpler than it is today, but it has
become quite misleading, especially with the advent of dyntick-idle
and NO_HZ_FULL.  The rcu_check_callbacks() function is RCU's hook into
the scheduling-clock interrupt, and is now but one of many ways that
callbacks get promoted to invocable state.

This commit therefore changes the name to rcu_sched_clock_irq(),
which is the same number of characters and clearly indicates this
function's relation to the rest of the Linux kernel.  In addition, for
the sake of consistency, rcu_flavor_check_callbacks() is also renamed
to rcu_flavor_sched_clock_irq().

While in the area, the header comments for both functions are reworked.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

doc.2018.08.30a: Documentation updates
dynticks.2018.08.30b: RCU flavor consolidation updates and cleanups
srcu.2018.08.30b: SRCU updates
torture.2018.08.29a: Torture-test updates