Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

!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>

	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

	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

	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

	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

	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:

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:

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.

	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

			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,

			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,

		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.