Merge branches 'rcu/torture', 'rcu/fixes', 'rcu/docs', 'rcu/refscale', 'rcu/tasks' and 'rcu/stall' into rcu/next

rcu/torture: RCU torture, locktorture and generic torture infrastructure
rcu/fixes: Generic and misc fixes
rcu/docs: RCU documentation updates
rcu/refscale: RCU reference scalability test updates
rcu/tasks: RCU tasks updates
rcu/stall: Stall detection updates

Author: Frederic Weisbecker

Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst

@@ -181,7 +181,7 @@ operations is carried out at several levels:
    of this wait (or series of waits, as the case may be) is to permit a
    concurrent CPU-hotplug operation to complete.
 #. In the case of RCU-sched, one of the last acts of an outgoing CPU is
-   to invoke ``rcu_report_dead()``, which reports a quiescent state for
+   to invoke ``rcutree_report_cpu_dead()``, which reports a quiescent state for
    that CPU. However, this is likely paranoia-induced redundancy.
 
 +-----------------------------------------------------------------------+

Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-registry.svg

@@ -1955,12 +1955,12 @@ if offline CPUs block an RCU grace period for too long.
 
 An offline CPU's quiescent state will be reported either:
 
-1.  As the CPU goes offline using RCU's hotplug notifier (rcu_report_dead()).
+1.  As the CPU goes offline using RCU's hotplug notifier (rcutree_report_cpu_dead()).
 2.  When grace period initialization (rcu_gp_init()) detects a
     race either with CPU offlining or with a task unblocking on a leaf
     ``rcu_node`` structure whose CPUs are all offline.
 
-The CPU-online path (rcu_cpu_starting()) should never need to report
+The CPU-online path (rcutree_report_cpu_starting()) should never need to report
 a quiescent state for an offline CPU.  However, as a debugging measure,
 it does emit a warning if a quiescent state was not already reported
 for that CPU.

Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg

@@ -8,6 +8,15 @@ One of the most common uses of RCU is protecting read-mostly linked lists
 that all of the required memory ordering is provided by the list macros.
 This document describes several list-based RCU use cases.
 
+When iterating a list while holding the rcu_read_lock(), writers may
+modify the list.  The reader is guaranteed to see all of the elements
+which were added to the list before they acquired the rcu_read_lock()
+and are still on the list when they drop the rcu_read_unlock().
+Elements which are added to, or removed from the list may or may not
+be seen.  If the writer calls list_replace_rcu(), the reader may see
+either the old element or the new element; they will not see both,
+nor will they see neither.
+
 
 Example 1: Read-mostly list: Deferred Destruction
 -------------------------------------------------

Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg

@@ -59,8 +59,8 @@ experiment with should focus on Section 2.  People who prefer to start
 with example uses should focus on Sections 3 and 4.  People who need to
 understand the RCU implementation should focus on Section 5, then dive
 into the kernel source code.  People who reason best by analogy should
-focus on Section 6.  Section 7 serves as an index to the docbook API
-documentation, and Section 8 is the traditional answer key.
+focus on Section 6 and 7.  Section 8 serves as an index to the docbook
+API documentation, and Section 9 is the traditional answer key.
 
 So, start with the section that makes the most sense to you and your
 preferred method of learning.  If you need to know everything about

Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg

@@ -4820,6 +4820,13 @@
 			Set maximum number of finished RCU callbacks to
 			process in one batch.
 
+	rcutree.do_rcu_barrier=	[KNL]
+			Request a call to rcu_barrier().  This is
+			throttled so that userspace tests can safely
+			hammer on the sysfs variable if they so choose.
+			If triggered before the RCU grace-period machinery
+			is fully active, this will error out with EAGAIN.
+
 	rcutree.dump_tree=	[KNL]
 			Dump the structure of the rcu_node combining tree
 			out at early boot.  This is used for diagnostic
@@ -5473,6 +5480,12 @@
 			test until boot completes in order to avoid
 			interference.
 
+	refscale.lookup_instances= [KNL]
+			Number of data elements to use for the forms of
+			SLAB_TYPESAFE_BY_RCU testing.  A negative number
+			is negated and multiplied by nr_cpu_ids, while
+			zero specifies nr_cpu_ids.
+
 	refscale.loops= [KNL]
 			Set the number of loops over the synchronization
 			primitive under test.  Increasing this number

Documentation/RCU/Design/Requirements/Requirements.rst

@@ -215,7 +215,7 @@ asmlinkage notrace void secondary_start_kernel(void)
 	if (system_uses_irq_prio_masking())
 		init_gic_priority_masking();
 
-	rcu_cpu_starting(cpu);
+	rcutree_report_cpu_starting(cpu);
 	trace_hardirqs_off();
 
 	/*
@@ -401,7 +401,7 @@ void __noreturn cpu_die_early(void)
 
 	/* Mark this CPU absent */
 	set_cpu_present(cpu, 0);
-	rcu_report_dead(cpu);
+	rcutree_report_cpu_dead();
 
 	if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
 		update_cpu_boot_status(CPU_KILL_ME);