Merge branch 'rcu/next' of... (bdd4431c) · Commits · 戴 / test

Documentation/RCU/RTFP.txt

+1745 −157

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Documentation/RCU/checklist.txt

+14 −0

Original line number	Diff line number	Diff line
		@@ -180,6 +180,20 @@ over a rather long period of time, but improvements are always welcome!
		operations that would not normally be undertaken while a real-time
		workload is running.

		In particular, if you find yourself invoking one of the expedited
		primitives repeatedly in a loop, please do everyone a favor:
		Restructure your code so that it batches the updates, allowing
		a single non-expedited primitive to cover the entire batch.
		This will very likely be faster than the loop containing the
		expedited primitive, and will be much much easier on the rest
		of the system, especially to real-time workloads running on
		the rest of the system.

		In addition, it is illegal to call the expedited forms from
		a CPU-hotplug notifier, or while holding a lock that is acquired
		by a CPU-hotplug notifier. Failing to observe this restriction
		will result in deadlock.

		7. If the updater uses call_rcu() or synchronize_rcu(), then the
		corresponding readers must use rcu_read_lock() and
		rcu_read_unlock(). If the updater uses call_rcu_bh() or

Documentation/RCU/stallwarn.txt

+80 −7

Original line number	Diff line number	Diff line
		@@ -12,14 +12,38 @@ 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
		ten seconds.
		sixty seconds.

		RCU_SECONDS_TILL_STALL_RECHECK
		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
		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
		timing of the next warning for the current stall.

		This macro defines the period of time that RCU will wait after
		issuing a stall warning until it issues another stall warning
		for the same stall. This time period is normally set to three
		times the check interval plus thirty seconds.
		Stall-warning messages may be enabled and disabled completely via
		/sys/module/rcutree/parameters/rcu_cpu_stall_suppress.

		CONFIG_RCU_CPU_STALL_VERBOSE

		This kernel configuration parameter causes the stall warning to
		also dump the stacks of any tasks that are blocking the current
		RCU-preempt grace period.

		RCU_CPU_STALL_INFO

		This kernel configuration parameter causes the stall warning to
		print out additional per-CPU diagnostic information, including
		information on scheduling-clock ticks and RCU's idle-CPU tracking.

		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.

		RCU_STALL_RAT_DELAY

		@@ -64,6 +88,54 @@ INFO: rcu_bh_state detected stalls on CPUs/tasks: { } (detected by 4, 2502 jiffi

		This is rare, but does happen from time to time in real life.

		If the CONFIG_RCU_CPU_STALL_INFO kernel configuration parameter is set,
		more information is printed with the stall-warning message, for example:

		INFO: rcu_preempt detected stall on CPU
		0: (63959 ticks this GP) idle=241/3fffffffffffffff/0
		(t=65000 jiffies)

		In kernels with CONFIG_RCU_FAST_NO_HZ, even more information is
		printed:

		INFO: rcu_preempt detected stall on CPU
		0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 drain=0 . timer=-1
		(t=65000 jiffies)

		The "(64628 ticks this GP)" indicates that this CPU has taken more
		than 64,000 scheduling-clock interrupts during the current stalled
		grace period. If the CPU was not yet aware of the current grace
		period (for example, if it was offline), then this part of the message
		indicates how many grace periods behind the CPU is.

		The "idle=" portion of the message prints the dyntick-idle state.
		The hex number before the first "/" is the low-order 12 bits of the
		dynticks counter, which will have an even-numbered value if the CPU is
		in dyntick-idle mode and an odd-numbered value otherwise. The hex
		number between the two "/"s is the value of the nesting, which will
		be a small positive number if in the idle loop and a very large positive
		number (as shown above) otherwise.

		For CONFIG_RCU_FAST_NO_HZ kernels, the "drain=0" indicates that the
		CPU is not in the process of trying to force itself into dyntick-idle
		state, the "." indicates that the CPU has not given up forcing RCU
		into dyntick-idle mode (it would be "H" otherwise), and the "timer=-1"
		indicates that the CPU has not recented forced RCU into dyntick-idle
		mode (it would otherwise indicate the number of microseconds remaining
		in this forced state).


		Multiple Warnings From One Stall

		If a stall lasts long enough, multiple stall-warning messages will be
		printed for it. The second and subsequent messages are printed at
		longer intervals, so that the time between (say) the first and second
		message will be about three times the interval between the beginning
		of the stall and the first message.


		What Causes RCU CPU Stall Warnings?

		So your kernel printed an RCU CPU stall warning. The next question is
		"What caused it?" The following problems can result in RCU CPU stall
		warnings:
		@@ -128,4 +200,5 @@ is occurring, which will usually be in the function nearest the top of
		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.
		RCU bugs can often be debugged with the help of CONFIG_RCU_TRACE
		and with RCU's event tracing.

Documentation/RCU/torture.txt

+30 −3

Original line number	Diff line number	Diff line
		@@ -69,6 +69,13 @@ onoff_interval
		CPU-hotplug operations regardless of what value is
		specified for onoff_interval.

		onoff_holdoff The number of seconds to wait until starting CPU-hotplug
		operations. This would normally only be used when
		rcutorture was built into the kernel and started
		automatically at boot time, in which case it is useful
		in order to avoid confusing boot-time code with CPUs
		coming and going.

		shuffle_interval
		The number of seconds to keep the test threads affinitied
		to a particular subset of the CPUs, defaults to 3 seconds.
		@@ -79,6 +86,24 @@ shutdown_secs The number of seconds to run the test before terminating
		zero, which disables test termination and system shutdown.
		This capability is useful for automated testing.

		stall_cpu The number of seconds that a CPU should be stalled while
		within both an rcu_read_lock() and a preempt_disable().
		This stall happens only once per rcutorture run.
		If you need multiple stalls, use modprobe and rmmod to
		repeatedly run rcutorture. The default for stall_cpu
		is zero, which prevents rcutorture from stalling a CPU.

		Note that attempts to rmmod rcutorture while the stall
		is ongoing will hang, so be careful what value you
		choose for this module parameter! In addition, too-large
		values for stall_cpu might well induce failures and
		warnings in other parts of the kernel. You have been
		warned!

		stall_cpu_holdoff
		The number of seconds to wait after rcutorture starts
		before stalling a CPU. Defaults to 10 seconds.

		stat_interval The number of seconds between output of torture
		statistics (via printk()). Regardless of the interval,
		statistics are printed when the module is unloaded.
		@@ -271,11 +296,13 @@ The following script may be used to torture RCU:
		#!/bin/sh

		modprobe rcutorture
		sleep 100
		sleep 3600
		rmmod rcutorture
		dmesg \| grep torture:

		The output can be manually inspected for the error flag of "!!!".
		One could of course create a more elaborate script that automatically
		checked for such errors. The "rmmod" command forces a "SUCCESS" or
		"FAILURE" indication to be printk()ed.
		checked for such errors. The "rmmod" command forces a "SUCCESS",
		"FAILURE", or "RCU_HOTPLUG" indication to be printk()ed. The first
		two are self-explanatory, while the last indicates that while there
		were no RCU failures, CPU-hotplug problems were detected.

Documentation/RCU/trace.txt

+16 −20

Original line number	Diff line number	Diff line
		@@ -33,23 +33,23 @@ rcu/rcuboost:
		The output of "cat rcu/rcudata" looks as follows:

		rcu_sched:
		0 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=545/1/0 df=50 of=0 ri=0 ql=163 qs=NRW. kt=0/W/0 ktl=ebc3 b=10 ci=153737 co=0 ca=0
		1 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=967/1/0 df=58 of=0 ri=0 ql=634 qs=NRW. kt=0/W/1 ktl=58c b=10 ci=191037 co=0 ca=0
		2 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1081/1/0 df=175 of=0 ri=0 ql=74 qs=N.W. kt=0/W/2 ktl=da94 b=10 ci=75991 co=0 ca=0
		3 c=20942 g=20943 pq=1 pgp=20942 qp=1 dt=1846/0/0 df=404 of=0 ri=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=72261 co=0 ca=0
		4 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=369/1/0 df=83 of=0 ri=0 ql=48 qs=N.W. kt=0/W/4 ktl=e0e7 b=10 ci=128365 co=0 ca=0
		5 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=381/1/0 df=64 of=0 ri=0 ql=169 qs=NRW. kt=0/W/5 ktl=fb2f b=10 ci=164360 co=0 ca=0
		6 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1037/1/0 df=183 of=0 ri=0 ql=62 qs=N.W. kt=0/W/6 ktl=d2ad b=10 ci=65663 co=0 ca=0
		7 c=20897 g=20897 pq=1 pgp=20896 qp=0 dt=1572/0/0 df=382 of=0 ri=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=75006 co=0 ca=0
		0 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=545/1/0 df=50 of=0 ql=163 qs=NRW. kt=0/W/0 ktl=ebc3 b=10 ci=153737 co=0 ca=0
		1 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=967/1/0 df=58 of=0 ql=634 qs=NRW. kt=0/W/1 ktl=58c b=10 ci=191037 co=0 ca=0
		2 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1081/1/0 df=175 of=0 ql=74 qs=N.W. kt=0/W/2 ktl=da94 b=10 ci=75991 co=0 ca=0
		3 c=20942 g=20943 pq=1 pgp=20942 qp=1 dt=1846/0/0 df=404 of=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=72261 co=0 ca=0
		4 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=369/1/0 df=83 of=0 ql=48 qs=N.W. kt=0/W/4 ktl=e0e7 b=10 ci=128365 co=0 ca=0
		5 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=381/1/0 df=64 of=0 ql=169 qs=NRW. kt=0/W/5 ktl=fb2f b=10 ci=164360 co=0 ca=0
		6 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1037/1/0 df=183 of=0 ql=62 qs=N.W. kt=0/W/6 ktl=d2ad b=10 ci=65663 co=0 ca=0
		7 c=20897 g=20897 pq=1 pgp=20896 qp=0 dt=1572/0/0 df=382 of=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=75006 co=0 ca=0
		rcu_bh:
		0 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=545/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/0 ktl=ebc3 b=10 ci=0 co=0 ca=0
		1 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=967/1/0 df=3 of=0 ri=1 ql=0 qs=.... kt=0/W/1 ktl=58c b=10 ci=151 co=0 ca=0
		2 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1081/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/2 ktl=da94 b=10 ci=0 co=0 ca=0
		3 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1846/0/0 df=8 of=0 ri=1 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=0 co=0 ca=0
		4 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=369/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/4 ktl=e0e7 b=10 ci=0 co=0 ca=0
		5 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=381/1/0 df=4 of=0 ri=1 ql=0 qs=.... kt=0/W/5 ktl=fb2f b=10 ci=0 co=0 ca=0
		6 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1037/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/6 ktl=d2ad b=10 ci=0 co=0 ca=0
		7 c=1474 g=1474 pq=1 pgp=1473 qp=0 dt=1572/0/0 df=8 of=0 ri=1 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=0 co=0 ca=0
		0 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=545/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/0 ktl=ebc3 b=10 ci=0 co=0 ca=0
		1 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=967/1/0 df=3 of=0 ql=0 qs=.... kt=0/W/1 ktl=58c b=10 ci=151 co=0 ca=0
		2 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1081/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/2 ktl=da94 b=10 ci=0 co=0 ca=0
		3 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1846/0/0 df=8 of=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=0 co=0 ca=0
		4 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=369/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/4 ktl=e0e7 b=10 ci=0 co=0 ca=0
		5 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=381/1/0 df=4 of=0 ql=0 qs=.... kt=0/W/5 ktl=fb2f b=10 ci=0 co=0 ca=0
		6 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1037/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/6 ktl=d2ad b=10 ci=0 co=0 ca=0
		7 c=1474 g=1474 pq=1 pgp=1473 qp=0 dt=1572/0/0 df=8 of=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=0 co=0 ca=0

		The first section lists the rcu_data structures for rcu_sched, the second
		for rcu_bh. Note that CONFIG_TREE_PREEMPT_RCU kernels will have an
		@@ -119,10 +119,6 @@ o "of" is the number of times that some other CPU has forced a
		CPU is offline when it is really alive and kicking) is a fatal
		error, so it makes sense to err conservatively.

		o "ri" is the number of times that RCU has seen fit to send a
		reschedule IPI to this CPU in order to get it to report a
		quiescent state.

		o "ql" is the number of RCU callbacks currently residing on
		this CPU. This is the total number of callbacks, regardless
		of what state they are in (new, waiting for grace period to

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