Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel…

…/git/paulmck/linux-rcu into core/rcu

Pull RCU updates from Paul E. McKenney:

 "The largest feature of this series is shrinking and simplification,
  with the following diffstat summary:

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

  In other words, this series represents a net reduction of more than 2700
  lines of code."

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

Documentation/RCU/00-INDEX

@@ -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

@@ -559,9 +559,7 @@ <h3><a name="Publish-Subscribe Guarantee">Publish/Subscribe Guarantee</a></h3>
 	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 @@ <h3><a name="Composability">Composability</a></h3>
 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 @@ <h2><a name="Software-Engineering Requirements">
 	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 @@ <h2><a name="Software-Engineering Requirements">
 	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 @@ <h3><a name="Energy Efficiency">Energy Efficiency</a></h3>
 <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 @@ <h3><a name="Sleepable RCU">Sleepable RCU</a></h3>
 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

@@ -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