The RCU requirements do not make it absolutely clear that the
memory-barrier requirements are not intended to replace the fundamental
requirement that all pre-existing RCU readers complete before a grace
period completes.  This commit therefore pulls the memory-barrier
requirements into a separate section and explicitly calls out the
relationship between the memory-barrier requirements and the fundamental
requirement.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit adds a second option for avoiding scheduler/RCU deadlocks,
namely that preemption be disabled across the entire RCU read-side
critical section in question.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit expands on RCU's composability by comparing it to that of
transactional memory and of locking.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit adds verbiage on boot and sysfs parameters that can be
used to control RCU CPU stall warnings, both to change the timeout
and to suppress these warnings entirely.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit records RCU's guarantee that the bottom bit of the rcu_head
structure's ->next field will remain zero for callbacks posted via
call_rcu(), but not necessarily for <tt>kfree_rcu()</tt> or some
possible future call_rcu_lazy() variant that might one day be created
for energy-efficiency purposese.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Updates URLs as suggested by Josh Triplett. ]

This commit adds RCU requirements as published in a 2015 LWN series.
Bringing these requirements in-tree allows them to be updated as changes
are discovered.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Updates to charset and URLs as suggested by Josh Triplett. ]