Merge branch 'rcu/next' of git://git.kernel.org/pub/scm/linux/kernel/…

…git/paulmck/linux-rcu into core/rcu

Pull RCU updates from Paul E. McKenney.

Major changes:

" 1.	Update RCU documentation.  These were posted to LKML at
	http://article.gmane.org/gmane.linux.kernel/1566994.

  2.	Miscellaneous fixes.  These were posted to LKML at
	http://article.gmane.org/gmane.linux.kernel/1567027.

  3.	Grace-period-related changes, primarily to aid in debugging,
	inspired by a -rt debugging session.  These were posted to
	LKML at http://article.gmane.org/gmane.linux.kernel/1567076.

  4.	Idle entry/exit changes, primarily to address issues located
	by Tibor Billes.  These were posted to LKML at
	http://article.gmane.org/gmane.linux.kernel/1567096.

  5.	Code reorganization moving RCU's source files from kernel
	to kernel/rcu.  This was posted to LKML at
	http://article.gmane.org/gmane.linux.kernel/1577344."

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Documentation/DocBook/device-drivers.tmpl

@@ -87,7 +87,10 @@ X!Iinclude/linux/kobject.h
 !Ekernel/printk/printk.c
 !Ekernel/panic.c
 !Ekernel/sys.c
-!Ekernel/rcupdate.c
+!Ekernel/rcu/srcu.c
+!Ekernel/rcu/tree.c
+!Ekernel/rcu/tree_plugin.h
+!Ekernel/rcu/update.c
      </sect1>
 
      <sect1><title>Device Resource Management</title>

Documentation/RCU/checklist.txt

@@ -202,8 +202,8 @@ over a rather long period of time, but improvements are always welcome!
 	updater uses call_rcu_sched() or synchronize_sched(), then
 	the corresponding readers must disable preemption, possibly
 	by calling rcu_read_lock_sched() and rcu_read_unlock_sched().
-	If the updater uses synchronize_srcu() or call_srcu(),
-	the the corresponding readers must use srcu_read_lock() and
+	If the updater uses synchronize_srcu() or call_srcu(), then
+	the corresponding readers must use srcu_read_lock() and
 	srcu_read_unlock(), and with the same srcu_struct.  The rules for
 	the expedited primitives are the same as for their non-expedited
 	counterparts.  Mixing things up will result in confusion and

Documentation/RCU/stallwarn.txt

@@ -12,12 +12,12 @@ CONFIG_RCU_CPU_STALL_TIMEOUT
 	This kernel configuration parameter defines the period of time
 	that RCU will wait from the beginning of a grace period until it
 	issues an RCU CPU stall warning.  This time period is normally
-	sixty seconds.
+	21 seconds.
 
 	This configuration parameter may be changed at runtime via the
 	/sys/module/rcutree/parameters/rcu_cpu_stall_timeout, however
 	this parameter is checked only at the beginning of a cycle.
-	So if you are 30 seconds into a 70-second stall, setting this
+	So if you are 10 seconds into a 40-second stall, setting this
 	sysfs parameter to (say) five will shorten the timeout for the
 	-next- stall, or the following warning for the current stall
 	(assuming the stall lasts long enough).  It will not affect the
@@ -32,7 +32,7 @@ CONFIG_RCU_CPU_STALL_VERBOSE
 	also dump the stacks of any tasks that are blocking the current
 	RCU-preempt grace period.
 
-RCU_CPU_STALL_INFO
+CONFIG_RCU_CPU_STALL_INFO
 
 	This kernel configuration parameter causes the stall warning to
 	print out additional per-CPU diagnostic information, including
@@ -43,7 +43,8 @@ RCU_STALL_DELAY_DELTA
 	Although the lockdep facility is extremely useful, it does add
 	some overhead.  Therefore, under CONFIG_PROVE_RCU, the
 	RCU_STALL_DELAY_DELTA macro allows five extra seconds before
-	giving an RCU CPU stall warning message.
+	giving an RCU CPU stall warning message.  (This is a cpp
+	macro, not a kernel configuration parameter.)
 
 RCU_STALL_RAT_DELAY
 
@@ -52,7 +53,8 @@ RCU_STALL_RAT_DELAY
 	However, if the offending CPU does not detect its own stall in
 	the number of jiffies specified by RCU_STALL_RAT_DELAY, then
 	some other CPU will complain.  This delay is normally set to
-	two jiffies.
+	two jiffies.  (This is a cpp macro, not a kernel configuration
+	parameter.)
 
 When a CPU detects that it is stalling, it will print a message similar
 to the following:
@@ -86,7 +88,12 @@ printing, there will be a spurious stall-warning message:
 
 INFO: rcu_bh_state detected stalls on CPUs/tasks: { } (detected by 4, 2502 jiffies)
 
-This is rare, but does happen from time to time in real life.
+This is rare, but does happen from time to time in real life.  It is also
+possible for a zero-jiffy stall to be flagged in this case, depending
+on how the stall warning and the grace-period initialization happen to
+interact.  Please note that it is not possible to entirely eliminate this
+sort of false positive without resorting to things like stop_machine(),
+which is overkill for this sort of problem.
 
 If the CONFIG_RCU_CPU_STALL_INFO kernel configuration parameter is set,
 more information is printed with the stall-warning message, for example:
@@ -216,4 +223,5 @@ that portion of the stack which remains the same from trace to trace.
 If you can reliably trigger the stall, ftrace can be quite helpful.
 
 RCU bugs can often be debugged with the help of CONFIG_RCU_TRACE
-and with RCU's event tracing.
+and with RCU's event tracing.  For information on RCU's event tracing,
+see include/trace/events/rcu.h.

Documentation/kernel-parameters.txt

@@ -2599,7 +2599,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	ramdisk_size=	[RAM] Sizes of RAM disks in kilobytes
 			See Documentation/blockdev/ramdisk.txt.
 
-	rcu_nocbs=	[KNL,BOOT]
+	rcu_nocbs=	[KNL]
 			In kernels built with CONFIG_RCU_NOCB_CPU=y, set
 			the specified list of CPUs to be no-callback CPUs.
 			Invocation of these CPUs' RCU callbacks will
@@ -2612,7 +2612,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			real-time workloads.  It can also improve energy
 			efficiency for asymmetric multiprocessors.
 
-	rcu_nocb_poll	[KNL,BOOT]
+	rcu_nocb_poll	[KNL]
 			Rather than requiring that offloaded CPUs
 			(specified by rcu_nocbs= above) explicitly
 			awaken the corresponding "rcuoN" kthreads,
@@ -2623,126 +2623,145 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			energy efficiency by requiring that the kthreads
 			periodically wake up to do the polling.
 
-	rcutree.blimit=	[KNL,BOOT]
+	rcutree.blimit=	[KNL]
 			Set maximum number of finished RCU callbacks to process
 			in one batch.
 
-	rcutree.fanout_leaf=	[KNL,BOOT]
+	rcutree.rcu_fanout_leaf= [KNL]
 			Increase the number of CPUs assigned to each
 			leaf rcu_node structure.  Useful for very large
 			systems.
 
-	rcutree.jiffies_till_first_fqs= [KNL,BOOT]
+	rcutree.jiffies_till_first_fqs= [KNL]
 			Set delay from grace-period initialization to
 			first attempt to force quiescent states.
 			Units are jiffies, minimum value is zero,
 			and maximum value is HZ.
 
-	rcutree.jiffies_till_next_fqs= [KNL,BOOT]
+	rcutree.jiffies_till_next_fqs= [KNL]
 			Set delay between subsequent attempts to force
 			quiescent states.  Units are jiffies, minimum
 			value is one, and maximum value is HZ.
 
-	rcutree.qhimark=	[KNL,BOOT]
+	rcutree.qhimark= [KNL]
 			Set threshold of queued
 			RCU callbacks over which batch limiting is disabled.
 
-	rcutree.qlowmark=	[KNL,BOOT]
+	rcutree.qlowmark= [KNL]
 			Set threshold of queued RCU callbacks below which
 			batch limiting is re-enabled.
 
-	rcutree.rcu_cpu_stall_suppress=	[KNL,BOOT]
-			Suppress RCU CPU stall warning messages.
-
-	rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
-			Set timeout for RCU CPU stall warning messages.
-
-	rcutree.rcu_idle_gp_delay=	[KNL,BOOT]
+	rcutree.rcu_idle_gp_delay= [KNL]
 			Set wakeup interval for idle CPUs that have
 			RCU callbacks (RCU_FAST_NO_HZ=y).
 
-	rcutree.rcu_idle_lazy_gp_delay=	[KNL,BOOT]
+	rcutree.rcu_idle_lazy_gp_delay= [KNL]
 			Set wakeup interval for idle CPUs that have
 			only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
 			Lazy RCU callbacks are those which RCU can
 			prove do nothing more than free memory.
 
-	rcutorture.fqs_duration= [KNL,BOOT]
+	rcutorture.fqs_duration= [KNL]
 			Set duration of force_quiescent_state bursts.
 
-	rcutorture.fqs_holdoff= [KNL,BOOT]
+	rcutorture.fqs_holdoff= [KNL]
 			Set holdoff time within force_quiescent_state bursts.
 
-	rcutorture.fqs_stutter= [KNL,BOOT]
+	rcutorture.fqs_stutter= [KNL]
 			Set wait time between force_quiescent_state bursts.
 
-	rcutorture.irqreader= [KNL,BOOT]
-			Test RCU readers from irq handlers.
+	rcutorture.gp_exp= [KNL]
+			Use expedited update-side primitives.
+
+	rcutorture.gp_normal= [KNL]
+			Use normal (non-expedited) update-side primitives.
+			If both gp_exp and gp_normal are set, do both.
+			If neither gp_exp nor gp_normal are set, still
+			do both.
 
-	rcutorture.n_barrier_cbs= [KNL,BOOT]
+	rcutorture.n_barrier_cbs= [KNL]
 			Set callbacks/threads for rcu_barrier() testing.
 
-	rcutorture.nfakewriters= [KNL,BOOT]
+	rcutorture.nfakewriters= [KNL]
 			Set number of concurrent RCU writers.  These just
 			stress RCU, they don't participate in the actual
 			test, hence the "fake".
 
-	rcutorture.nreaders= [KNL,BOOT]
+	rcutorture.nreaders= [KNL]
 			Set number of RCU readers.
 
-	rcutorture.onoff_holdoff= [KNL,BOOT]
+	rcutorture.object_debug= [KNL]
+			Enable debug-object double-call_rcu() testing.
+
+	rcutorture.onoff_holdoff= [KNL]
 			Set time (s) after boot for CPU-hotplug testing.
 
-	rcutorture.onoff_interval= [KNL,BOOT]
+	rcutorture.onoff_interval= [KNL]
 			Set time (s) between CPU-hotplug operations, or
 			zero to disable CPU-hotplug testing.
 
-	rcutorture.shuffle_interval= [KNL,BOOT]
+	rcutorture.rcutorture_runnable= [BOOT]
+			Start rcutorture running at boot time.
+
+	rcutorture.shuffle_interval= [KNL]
 			Set task-shuffle interval (s).  Shuffling tasks
 			allows some CPUs to go into dyntick-idle mode
 			during the rcutorture test.
 
-	rcutorture.shutdown_secs= [KNL,BOOT]
+	rcutorture.shutdown_secs= [KNL]
 			Set time (s) after boot system shutdown.  This
 			is useful for hands-off automated testing.
 
-	rcutorture.stall_cpu= [KNL,BOOT]
+	rcutorture.stall_cpu= [KNL]
 			Duration of CPU stall (s) to test RCU CPU stall
 			warnings, zero to disable.
 
-	rcutorture.stall_cpu_holdoff= [KNL,BOOT]
+	rcutorture.stall_cpu_holdoff= [KNL]
 			Time to wait (s) after boot before inducing stall.
 
-	rcutorture.stat_interval= [KNL,BOOT]
+	rcutorture.stat_interval= [KNL]
 			Time (s) between statistics printk()s.
 
-	rcutorture.stutter= [KNL,BOOT]
+	rcutorture.stutter= [KNL]
 			Time (s) to stutter testing, for example, specifying
 			five seconds causes the test to run for five seconds,
 			wait for five seconds, and so on.  This tests RCU's
 			ability to transition abruptly to and from idle.
 
-	rcutorture.test_boost= [KNL,BOOT]
+	rcutorture.test_boost= [KNL]
 			Test RCU priority boosting?  0=no, 1=maybe, 2=yes.
 			"Maybe" means test if the RCU implementation
 			under test support RCU priority boosting.
 
-	rcutorture.test_boost_duration= [KNL,BOOT]
+	rcutorture.test_boost_duration= [KNL]
 			Duration (s) of each individual boost test.
 
-	rcutorture.test_boost_interval= [KNL,BOOT]
+	rcutorture.test_boost_interval= [KNL]
 			Interval (s) between each boost test.
 
-	rcutorture.test_no_idle_hz= [KNL,BOOT]
+	rcutorture.test_no_idle_hz= [KNL]
 			Test RCU's dyntick-idle handling.  See also the
 			rcutorture.shuffle_interval parameter.
 
-	rcutorture.torture_type= [KNL,BOOT]
+	rcutorture.torture_type= [KNL]
 			Specify the RCU implementation to test.
 
-	rcutorture.verbose= [KNL,BOOT]
+	rcutorture.verbose= [KNL]
 			Enable additional printk() statements.
 
+	rcupdate.rcu_expedited= [KNL]
+			Use expedited grace-period primitives, for
+			example, synchronize_rcu_expedited() instead
+			of synchronize_rcu().  This reduces latency,
+			but can increase CPU utilization, degrade
+			real-time latency, and degrade energy efficiency.
+
+	rcupdate.rcu_cpu_stall_suppress= [KNL]
+			Suppress RCU CPU stall warning messages.
+
+	rcupdate.rcu_cpu_stall_timeout= [KNL]
+			Set timeout for RCU CPU stall warning messages.
+
 	rdinit=		[KNL]
 			Format: <full_path>
 			Run specified binary instead of /init from the ramdisk,

Documentation/kernel-per-CPU-kthreads.txt

@@ -181,12 +181,17 @@ To reduce its OS jitter, do any of the following:
 		make sure that this is safe on your particular system.
 	d.	It is not possible to entirely get rid of OS jitter
 		from vmstat_update() on CONFIG_SMP=y systems, but you
-		can decrease its frequency by writing a large value to
-		/proc/sys/vm/stat_interval.  The default value is HZ,
-		for an interval of one second.  Of course, larger values
-		will make your virtual-memory statistics update more
-		slowly.  Of course, you can also run your workload at
-		a real-time priority, thus preempting vmstat_update().
+		can decrease its frequency by writing a large value
+		to /proc/sys/vm/stat_interval.	The default value is
+		HZ, for an interval of one second.  Of course, larger
+		values will make your virtual-memory statistics update
+		more slowly.  Of course, you can also run your workload
+		at a real-time priority, thus preempting vmstat_update(),
+		but if your workload is CPU-bound, this is a bad idea.
+		However, there is an RFC patch from Christoph Lameter
+		(based on an earlier one from Gilad Ben-Yossef) that
+		reduces or even eliminates vmstat overhead for some
+		workloads at https://lkml.org/lkml/2013/9/4/379.
 	e.	If running on high-end powerpc servers, build with
 		CONFIG_PPC_RTAS_DAEMON=n.  This prevents the RTAS
 		daemon from running on each CPU every second or so.

MAINTAINERS

@@ -6935,7 +6935,7 @@ M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
 F:	Documentation/RCU/torture.txt
-F:	kernel/rcutorture.c
+F:	kernel/rcu/torture.c
 
 RDC R-321X SoC
 M:	Florian Fainelli <florian@openwrt.org>
@@ -6962,8 +6962,9 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
 F:	Documentation/RCU/
 X:	Documentation/RCU/torture.txt
 F:	include/linux/rcu*
-F:	kernel/rcu*
-X:	kernel/rcutorture.c
+X:	include/linux/srcu.h
+F:	kernel/rcu/
+X:	kernel/rcu/torture.c
 
 REAL TIME CLOCK (RTC) SUBSYSTEM
 M:	Alessandro Zummo <a.zummo@towertech.it>
@@ -7650,8 +7651,8 @@ M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
 W:	http://www.rdrop.com/users/paulmck/RCU/
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
-F:	include/linux/srcu*
-F:	kernel/srcu*
+F:	include/linux/srcu.h
+F:	kernel/rcu/srcu.c
 
 SMACK SECURITY MODULE
 M:	Casey Schaufler <casey@schaufler-ca.com>

include/linux/rculist.h

@@ -18,6 +18,21 @@
  * be used anywhere you would want to use a list_empty_rcu().
  */
 
+/*
+ * INIT_LIST_HEAD_RCU - Initialize a list_head visible to RCU readers
+ * @list: list to be initialized
+ *
+ * You should instead use INIT_LIST_HEAD() for normal initialization and
+ * cleanup tasks, when readers have no access to the list being initialized.
+ * However, if the list being initialized is visible to readers, you
+ * need to keep the compiler from being too mischievous.
+ */
+static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
+{
+	ACCESS_ONCE(list->next) = list;
+	ACCESS_ONCE(list->prev) = list;
+}
+
 /*
  * return the ->next pointer of a list_head in an rcu safe
  * way, we must not access it directly
@@ -191,9 +206,13 @@ static inline void list_splice_init_rcu(struct list_head *list,
 	if (list_empty(list))
 		return;
 
-	/* "first" and "last" tracking list, so initialize it. */
+	/*
+	 * "first" and "last" tracking list, so initialize it.  RCU readers
+	 * have access to this list, so we must use INIT_LIST_HEAD_RCU()
+	 * instead of INIT_LIST_HEAD().
+	 */
 
-	INIT_LIST_HEAD(list);
+	INIT_LIST_HEAD_RCU(list);
 
 	/*
 	 * At this point, the list body still points to the source list.