Commit 330e9e46 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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

Pull RCU updates from Ingo Molnar:
 "The sole purpose of these changes is to shrink and simplify the RCU
  code base, which has suffered from creeping bloat over the past couple
  of years. The end result is a net removal of ~2700 lines of code:

     79 files changed, 1496 insertions(+), 4211 deletions(-)

  Plus there's a marked reduction in the Kconfig space complexity as
  well, here's the number of matches on 'grep RCU' in the .config:

                               before       after

     x86-defconfig                 17          15
     x86-allmodconfig              33          20"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (86 commits)
  rcu: Remove RCU CPU stall warnings from Tiny RCU
  rcu: Remove event tracing from Tiny RCU
  rcu: Move RCU debug Kconfig options to kernel/rcu
  rcu: Move RCU non-debug Kconfig options to kernel/rcu
  rcu: Eliminate NOCBs CPU-state Kconfig options
  rcu: Remove debugfs tracing
  srcu: Remove Classic SRCU
  srcu: Fix rcutorture-statistics typo
  rcu: Remove SPARSE_RCU_POINTER Kconfig option
  rcu: Remove the now-obsolete PROVE_RCU_REPEATEDLY Kconfig option
  rcu: Remove typecheck() from RCU locking wrapper functions
  rcu: Remove #ifdef moving rcu_end_inkernel_boot from rcupdate.h
  rcu: Remove nohz_full full-system-idle state machine
  rcu: Remove the RCU_KTHREAD_PRIO Kconfig option
  rcu: Remove *_SLOW_* Kconfig options
  srcu: Use rnp->lock wrappers to replace explicit memory barriers
  rcu: Move rnp->lock wrappers for SRCU use
  rcu: Convert rnp->lock wrappers to macros for SRCU use
  rcu: Refactor #includes from include/linux/rcupdate.h
  bcm47xx: Fix build regression
  ...
parents e94693f7 567b64aa

Documentation/RCU/00-INDEX

+0 −2
Original line number Diff line number Diff line
@@ -28,8 +28,6 @@ stallwarn.txt 
	- RCU CPU stall warnings (module parameter rcu_cpu_stall_suppress)

torture.txt

	- RCU Torture Test Operation (CONFIG_RCU_TORTURE_TEST)

trace.txt

	- CONFIG_RCU_TRACE debugfs files and formats

UP.txt

	- RCU on Uniprocessor Systems

whatisRCU.txt

Documentation/RCU/Design/Requirements/Requirements.html

+21 −13
Original line number Diff line number Diff line
@@ -559,9 +559,7 @@ The <tt>rcu_access_pointer()</tt> on line&nbsp;6 is similar to 
	For <tt>remove_gp_synchronous()</tt>, as long as all modifications

	to <tt>gp</tt> are carried out while holding <tt>gp_lock</tt>,

	the above optimizations are harmless.

	However,

	with <tt>CONFIG_SPARSE_RCU_POINTER=y</tt>,

	<tt>sparse</tt> will complain if you

	However, <tt>sparse</tt> will complain if you

	define <tt>gp</tt> with <tt>__rcu</tt> and then

	access it without using

	either <tt>rcu_access_pointer()</tt> or <tt>rcu_dereference()</tt>.
@@ -1849,7 +1847,8 @@ mass storage, or user patience, whichever comes first. 
If the nesting is not visible to the compiler, as is the case with

mutually recursive functions each in its own translation unit,

stack overflow will result.

If the nesting takes the form of loops, either the control variable

If the nesting takes the form of loops, perhaps in the guise of tail

recursion, either the control variable

will overflow or (in the Linux kernel) you will get an RCU CPU stall warning.

Nevertheless, this class of RCU implementations is one

of the most composable constructs in existence.
@@ -1977,9 +1976,8 @@ guard against mishaps and misuse: 
	and <tt>rcu_dereference()</tt>, perhaps (incorrectly)

	substituting a simple assignment.

	To catch this sort of error, a given RCU-protected pointer may be

	tagged with <tt>__rcu</tt>, after which running sparse

	with <tt>CONFIG_SPARSE_RCU_POINTER=y</tt> will complain

	about simple-assignment accesses to that pointer.

	tagged with <tt>__rcu</tt>, after which sparse

	will complain about simple-assignment accesses to that pointer.

	Arnd Bergmann made me aware of this requirement, and also

	supplied the needed

	<a href="https://lwn.net/Articles/376011/">patch series</a>.
@@ -2036,7 +2034,7 @@ guard against mishaps and misuse: 
	some other synchronization mechanism, for example, reference

	counting.

<li>	In kernels built with <tt>CONFIG_RCU_TRACE=y</tt>, RCU-related

	information is provided via both debugfs and event tracing.

	information is provided via event tracing.

<li>	Open-coded use of <tt>rcu_assign_pointer()</tt> and

	<tt>rcu_dereference()</tt> to create typical linked

	data structures can be surprisingly error-prone.
@@ -2519,11 +2517,7 @@ It is similarly socially unacceptable to interrupt an 
<tt>nohz_full</tt> CPU running in userspace.

RCU must therefore track <tt>nohz_full</tt> userspace

execution.

And in

<a href="https://lwn.net/Articles/558284/"><tt>CONFIG_NO_HZ_FULL_SYSIDLE=y</tt></a>

kernels, RCU must separately track idle CPUs on the one hand and

CPUs that are either idle or executing in userspace on the other.

In both cases, RCU must be able to sample state at two points in

RCU must therefore be able to sample state at two points in

time, and be able to determine whether or not some other CPU spent

any time idle and/or executing in userspace.
@@ -2935,6 +2929,20 @@ The reason that this is possible is that SRCU is insensitive 
to whether or not a CPU is online, which means that <tt>srcu_barrier()</tt>

need not exclude CPU-hotplug operations.



<p>

SRCU also differs from other RCU flavors in that SRCU's expedited and

non-expedited grace periods are implemented by the same mechanism.

This means that in the current SRCU implementation, expediting a

future grace period has the side effect of expediting all prior

grace periods that have not yet completed.

(But please note that this is a property of the current implementation,

not necessarily of future implementations.)

In addition, if SRCU has been idle for longer than the interval

specified by the <tt>srcutree.exp_holdoff</tt> kernel boot parameter

(25&nbsp;microseconds by default),

and if a <tt>synchronize_srcu()</tt> invocation ends this idle period,

that invocation will be automatically expedited.



<p>

As of v4.12, SRCU's callbacks are maintained per-CPU, eliminating

a locking bottleneck present in prior kernel versions.

Documentation/RCU/checklist.txt

+4 −4
Original line number Diff line number Diff line
@@ -413,11 +413,11 @@ over a rather long period of time, but improvements are always welcome! 
	read-side critical sections.  It is the responsibility of the

	RCU update-side primitives to deal with this.



17.	Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and the

	__rcu sparse checks (enabled by CONFIG_SPARSE_RCU_POINTER) to

	validate your RCU code.  These can help find problems as follows:

17.	Use CONFIG_PROVE_LOCKING, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and the

	__rcu sparse checks to validate your RCU code.	These can help

	find problems as follows:



	CONFIG_PROVE_RCU: check that accesses to RCU-protected data

	CONFIG_PROVE_LOCKING: check that accesses to RCU-protected data

		structures are carried out under the proper RCU

		read-side critical section, while holding the right

		combination of locks, or whatever other conditions

Documentation/RCU/trace.txt

deleted100644 → 0
+0 −535

File deleted.

Preview size limit exceeded, changes collapsed.

Documentation/admin-guide/kernel-parameters.txt

+31 −10
Original line number Diff line number Diff line
@@ -3238,21 +3238,17 @@ 


	rcutree.gp_cleanup_delay=	[KNL]

			Set the number of jiffies to delay each step of

			RCU grace-period cleanup.  This only has effect

			when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.

			RCU grace-period cleanup.



	rcutree.gp_init_delay=	[KNL]

			Set the number of jiffies to delay each step of

			RCU grace-period initialization.  This only has

			effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT

			is set.

			RCU grace-period initialization.



	rcutree.gp_preinit_delay=	[KNL]

			Set the number of jiffies to delay each step of

			RCU grace-period pre-initialization, that is,

			the propagation of recent CPU-hotplug changes up

			the rcu_node combining tree.  This only has effect

			when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.

			the rcu_node combining tree.



	rcutree.rcu_fanout_exact= [KNL]

			Disable autobalancing of the rcu_node combining
@@ -3328,6 +3324,17 @@ 
			This wake_up() will be accompanied by a

			WARN_ONCE() splat and an ftrace_dump().



	rcuperf.gp_async= [KNL]

			Measure performance of asynchronous

			grace-period primitives such as call_rcu().



	rcuperf.gp_async_max= [KNL]

			Specify the maximum number of outstanding

			callbacks per writer thread.  When a writer

			thread exceeds this limit, it invokes the

			corresponding flavor of rcu_barrier() to allow

			previously posted callbacks to drain.



	rcuperf.gp_exp= [KNL]

			Measure performance of expedited synchronous

			grace-period primitives.
@@ -3355,17 +3362,22 @@ 
	rcuperf.perf_runnable= [BOOT]

			Start rcuperf running at boot time.



	rcuperf.perf_type= [KNL]

			Specify the RCU implementation to test.



	rcuperf.shutdown= [KNL]

			Shut the system down after performance tests

			complete.  This is useful for hands-off automated

			testing.



	rcuperf.perf_type= [KNL]

			Specify the RCU implementation to test.



	rcuperf.verbose= [KNL]

			Enable additional printk() statements.



	rcuperf.writer_holdoff= [KNL]

			Write-side holdoff between grace periods,

			in microseconds.  The default of zero says

			no holdoff.



	rcutorture.cbflood_inter_holdoff= [KNL]

			Set holdoff time (jiffies) between successive

			callback-flood tests.
@@ -3803,6 +3815,15 @@ 
	spia_pedr=

	spia_peddr=



	srcutree.counter_wrap_check [KNL]

			Specifies how frequently to check for

			grace-period sequence counter wrap for the

			srcu_data structure's ->srcu_gp_seq_needed field.

			The greater the number of bits set in this kernel

			parameter, the less frequently counter wrap will

			be checked for.  Note that the bottom two bits

			are ignored.



	srcutree.exp_holdoff [KNL]

			Specifies how many nanoseconds must elapse

			since the end of the last SRCU grace period for

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