Because the ->dynticks_nesting field now only contains the process-based
nesting level instead of a value encoding both the process nesting level
and the irq "nesting" level, we no longer need a long long, even on
32-bit systems.  This commit therefore changes both the ->dynticks_nesting
and ->dynticks_nmi_nesting fields to long.

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

Now that ->dynticks_nesting counts only process-level dyntick-idle
entry and exit, there is no need for the elaborate segmented counter
with its guard fields and overflow checking.  This commit therefore
makes ->dynticks_nesting be a simple counter.

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

One common question upon seeing an RCU CPU stall warning is "did
the stalled CPUs have interrupts disabled?"  However, the current
stall warnings are silent on this point.  This commit therefore
uses irq_work to check whether stalled CPUs still respond to IPIs,
and flags this state in the RCU CPU stall warning console messages.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

doc.2017.08.17a: Documentation updates.
fixes.2017.08.17a: RCU fixes.
hotplug.2017.07.25b: CPU-hotplug updates.
misc.2017.08.17a: Miscellaneous fixes outside of RCU (give or take conflicts).
spin_unlock_wait_no.2017.08.17a: Remove spin_unlock_wait().
srcu.2017.07.27c: SRCU updates.
torture.2017.07.24c: Torture-test updates.

Given that the rcu_state structure's >orphan_pend and ->orphan_done
fields are used only during migration of callbacks from the recently
offlined CPU to a surviving CPU, if rcu_send_cbs_to_orphanage() and
rcu_adopt_orphan_cbs() are combined, these fields can become local
variables in the combined function.  This commit therefore combines
rcu_send_cbs_to_orphanage() and rcu_adopt_orphan_cbs() into a new
rcu_segcblist_merge() function and removes the ->orphan_pend and
->orphan_done fields.

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

The ->orphan_lock is acquired and released only within the
rcu_migrate_callbacks() function, which now acquires the root rcu_node
structure's ->lock.  This commit therefore eliminates the ->orphan_lock
in favor of the root rcu_node structure's ->lock.

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

RCU's CPU-hotplug callback-migration code first moves the outgoing
CPU's callbacks to ->orphan_done and ->orphan_pend, and only then
moves them to the NOCB callback list.  This commit avoids the
extra step (and simplifies the code) by moving the callbacks directly
from the outgoing CPU's callback list to the NOCB callback list.

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

The rcu_node structure's ->n_cbs_orphaned and ->n_cbs_adopted fields
are updated, but never read.  This commit therefore removes them.

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

The handling of RCU's no-CBs CPUs has a maintenance headache, namely
that if call_rcu() is invoked with interrupts disabled, the rcuo kthread
wakeup must be defered to a point where we can be sure that scheduler
locks are not held.  Of course, there are a lot of code paths leading
from an interrupts-disabled invocation of call_rcu(), and missing any
one of these can result in excessive callback-invocation latency, and
potentially even system hangs.

This commit therefore uses a timer to guarantee that the wakeup will
eventually occur.  If one of the deferred-wakeup points kicks in, then
the timer is simply cancelled.

This commit also fixes up an incomplete removal of commits that were
intended to plug remaining exit paths, which should have the added
benefit of reducing the overhead of RCU's context-switch hooks.  In
addition, it simplifies leader-to-follower callback-list handoff by
introducing locking.  The call_rcu()-to-leader handoff continues to
use atomic operations in order to maintain good real-time latency for
common-case use of call_rcu().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Dan Carpenter fix for mod_timer() usage bug found by smatch. ]

RCU's debugfs tracing used to be the only reasonable low-level debug
information available, but ftrace and event tracing has since surpassed
the RCU debugfs level of usefulness.  This commit therefore removes
RCU's debugfs tracing.

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