Merge tag 'rcu.2023.06.22a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU updates from Paul McKenney:
 "Documentation updates

  Miscellaneous fixes, perhaps most notably:

   - Remove RCU_NONIDLE(). The new visibility of most of the idle loop
     to RCU has obsoleted this API.

   - Make the RCU_SOFTIRQ callback-invocation time limit also apply to
     the rcuc kthreads that invoke callbacks for CONFIG_PREEMPT_RT.

   - Add a jiffies-based callback-invocation time limit to handle
     long-running callbacks. (The local_clock() function is only invoked
     once per 32 callbacks due to its high overhead.)

   - Stop rcu_tasks_invoke_cbs() from using never-onlined CPUs, which
     fixes a bug that can occur on systems with non-contiguous CPU
     numbering.

  kvfree_rcu updates:

   - Eliminate the single-argument variant of k[v]free_rcu() now that
     all uses have been converted to k[v]free_rcu_mightsleep().

   - Add WARN_ON_ONCE() checks for k[v]free_rcu*() freeing callbacks too
     soon. Yes, this is closing the barn door after the horse has
     escaped, but Murphy says that there will be more horses.

  Callback-offloading updates:

   - Fix a number of bugs involving the shrinker and lazy callbacks.

  Tasks RCU updates

  Torture-test updates"

* tag 'rcu.2023.06.22a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (32 commits)
  torture: Remove duplicated argument -enable-kvm for ppc64
  doc/rcutorture: Add description of rcutorture.stall_cpu_block
  rcu/rcuscale: Stop kfree_scale_thread thread(s) after unloading rcuscale
  rcu/rcuscale: Move rcu_scale_*() after kfree_scale_cleanup()
  rcutorture: Correct name of use_softirq module parameter
  locktorture: Add long_hold to adjust lock-hold delays
  rcu/nocb: Make shrinker iterate only over NOCB CPUs
  rcu-tasks: Stop rcu_tasks_invoke_cbs() from using never-onlined CPUs
  rcu: Make rcu_cpu_starting() rely on interrupts being disabled
  rcu: Mark rcu_cpu_kthread() accesses to ->rcu_cpu_has_work
  rcu: Mark additional concurrent load from ->cpu_no_qs.b.exp
  rcu: Employ jiffies-based backstop to callback time limit
  rcu: Check callback-invocation time limit for rcuc kthreads
  rcu: Remove RCU_NONIDLE()
  rcu: Add more RCU files to kernel-api.rst
  rcu-tasks: Clarify the cblist_init_generic() function's pr_info() output
  rcu-tasks: Avoid pr_info() with spin lock in cblist_init_generic()
  rcu/nocb: Recheck lazy callbacks under the ->nocb_lock from shrinker
  rcu/nocb: Fix shrinker race against callback enqueuer
  rcu/nocb: Protect lazy shrinker against concurrent (de-)offloading
  ...

4 files changed, 91 insertions, 98 deletions

diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index 49387d823619..f3b605285a87 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.rst
+++ b/Documentation/RCU/Design/Requirements/Requirements.rst
@@ -2071,41 +2071,7 @@ call.
 
 Because RCU avoids interrupting idle CPUs, it is illegal to execute an
 RCU read-side critical section on an idle CPU. (Kernels built with
-``CONFIG_PROVE_RCU=y`` will splat if you try it.) The RCU_NONIDLE()
-macro and ``_rcuidle`` event tracing is provided to work around this
-restriction. In addition, rcu_is_watching() may be used to test
-whether or not it is currently legal to run RCU read-side critical
-sections on this CPU. I learned of the need for diagnostics on the one
-hand and RCU_NONIDLE() on the other while inspecting idle-loop code.
-Steven Rostedt supplied ``_rcuidle`` event tracing, which is used quite
-heavily in the idle loop. However, there are some restrictions on the
-code placed within RCU_NONIDLE():
-
-#. Blocking is prohibited. In practice, this is not a serious
-   restriction given that idle tasks are prohibited from blocking to
-   begin with.
-#. Although nesting RCU_NONIDLE() is permitted, they cannot nest
-   indefinitely deeply. However, given that they can be nested on the
-   order of a million deep, even on 32-bit systems, this should not be a
-   serious restriction. This nesting limit would probably be reached
-   long after the compiler OOMed or the stack overflowed.
-#. Any code path that enters RCU_NONIDLE() must sequence out of that
-   same RCU_NONIDLE(). For example, the following is grossly
-   illegal:
-
-      ::
-
-	  1     RCU_NONIDLE({
-	  2       do_something();
-	  3       goto bad_idea;  /* BUG!!! */
-	  4       do_something_else();});
-	  5   bad_idea:
-
-
-   It is just as illegal to transfer control into the middle of
-   RCU_NONIDLE()'s argument. Yes, in theory, you could transfer in
-   as long as you also transferred out, but in practice you could also
-   expect to get sharply worded review comments.
+``CONFIG_PROVE_RCU=y`` will splat if you try it.)
 
 It is similarly socially unacceptable to interrupt an ``nohz_full`` CPU
 running in userspace. RCU must therefore track ``nohz_full`` userspace
diff --git a/Documentation/RCU/whatisRCU.rst b/Documentation/RCU/whatisRCU.rst
index 8eddef28d3a1..e488c8e557a9 100644
--- a/Documentation/RCU/whatisRCU.rst
+++ b/Documentation/RCU/whatisRCU.rst
@@ -1117,7 +1117,6 @@ All: lockdep-checked RCU utility APIs::
 
 	RCU_LOCKDEP_WARN
 	rcu_sleep_check
-	RCU_NONIDLE
 
 All: Unchecked RCU-protected pointer access::
 
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index c5e7bb4babf0..2836780618a8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4731,43 +4731,6 @@
 			the propagation of recent CPU-hotplug changes up
 			the rcu_node combining tree.
 
-	rcutree.use_softirq=	[KNL]
-			If set to zero, move all RCU_SOFTIRQ processing to
-			per-CPU rcuc kthreads.  Defaults to a non-zero
-			value, meaning that RCU_SOFTIRQ is used by default.
-			Specify rcutree.use_softirq=0 to use rcuc kthreads.
-
-			But note that CONFIG_PREEMPT_RT=y kernels disable
-			this kernel boot parameter, forcibly setting it
-			to zero.
-
-	rcutree.rcu_fanout_exact= [KNL]
-			Disable autobalancing of the rcu_node combining
-			tree.  This is used by rcutorture, and might
-			possibly be useful for architectures having high
-			cache-to-cache transfer latencies.
-
-	rcutree.rcu_fanout_leaf= [KNL]
-			Change the number of CPUs assigned to each
-			leaf rcu_node structure.  Useful for very
-			large systems, which will choose the value 64,
-			and for NUMA systems with large remote-access
-			latencies, which will choose a value aligned
-			with the appropriate hardware boundaries.
-
-	rcutree.rcu_min_cached_objs= [KNL]
-			Minimum number of objects which are cached and
-			maintained per one CPU. Object size is equal
-			to PAGE_SIZE. The cache allows to reduce the
-			pressure to page allocator, also it makes the
-			whole algorithm to behave better in low memory
-			condition.
-
-	rcutree.rcu_delay_page_cache_fill_msec= [KNL]
-			Set the page-cache refill delay (in milliseconds)
-			in response to low-memory conditions.  The range
-			of permitted values is in the range 0:100000.
-
 	rcutree.jiffies_till_first_fqs= [KNL]
 			Set delay from grace-period initialization to
 			first attempt to force quiescent states.
@@ -4806,21 +4769,6 @@
 			When RCU_NOCB_CPU is set, also adjust the
 			priority of NOCB callback kthreads.
 
-	rcutree.rcu_divisor= [KNL]
-			Set the shift-right count to use to compute
-			the callback-invocation batch limit bl from
-			the number of callbacks queued on this CPU.
-			The result will be bounded below by the value of
-			the rcutree.blimit kernel parameter.  Every bl
-			callbacks, the softirq handler will exit in
-			order to allow the CPU to do other work.
-
-			Please note that this callback-invocation batch
-			limit applies only to non-offloaded callback
-			invocation.  Offloaded callbacks are instead
-			invoked in the context of an rcuoc kthread, which
-			scheduler will preempt as it does any other task.
-
 	rcutree.nocb_nobypass_lim_per_jiffy= [KNL]
 			On callback-offloaded (rcu_nocbs) CPUs,
 			RCU reduces the lock contention that would
@@ -4834,14 +4782,6 @@
 			the ->nocb_bypass queue.  The definition of "too
 			many" is supplied by this kernel boot parameter.
 
-	rcutree.rcu_nocb_gp_stride= [KNL]
-			Set the number of NOCB callback kthreads in
-			each group, which defaults to the square root
-			of the number of CPUs.	Larger numbers reduce
-			the wakeup overhead on the global grace-period
-			kthread, but increases that same overhead on
-			each group's NOCB grace-period kthread.
-
 	rcutree.qhimark= [KNL]
 			Set threshold of queued RCU callbacks beyond which
 			batch limiting is disabled.
@@ -4859,6 +4799,56 @@
 			on rcutree.qhimark at boot time and to zero to
 			disable more aggressive help enlistment.
 
+	rcutree.rcu_delay_page_cache_fill_msec= [KNL]
+			Set the page-cache refill delay (in milliseconds)
+			in response to low-memory conditions.  The range
+			of permitted values is in the range 0:100000.
+
+	rcutree.rcu_divisor= [KNL]
+			Set the shift-right count to use to compute
+			the callback-invocation batch limit bl from
+			the number of callbacks queued on this CPU.
+			The result will be bounded below by the value of
+			the rcutree.blimit kernel parameter.  Every bl
+			callbacks, the softirq handler will exit in
+			order to allow the CPU to do other work.
+
+			Please note that this callback-invocation batch
+			limit applies only to non-offloaded callback
+			invocation.  Offloaded callbacks are instead
+			invoked in the context of an rcuoc kthread, which
+			scheduler will preempt as it does any other task.
+
+	rcutree.rcu_fanout_exact= [KNL]
+			Disable autobalancing of the rcu_node combining
+			tree.  This is used by rcutorture, and might
+			possibly be useful for architectures having high
+			cache-to-cache transfer latencies.
+
+	rcutree.rcu_fanout_leaf= [KNL]
+			Change the number of CPUs assigned to each
+			leaf rcu_node structure.  Useful for very
+			large systems, which will choose the value 64,
+			and for NUMA systems with large remote-access
+			latencies, which will choose a value aligned
+			with the appropriate hardware boundaries.
+
+	rcutree.rcu_min_cached_objs= [KNL]
+			Minimum number of objects which are cached and
+			maintained per one CPU. Object size is equal
+			to PAGE_SIZE. The cache allows to reduce the
+			pressure to page allocator, also it makes the
+			whole algorithm to behave better in low memory
+			condition.
+
+	rcutree.rcu_nocb_gp_stride= [KNL]
+			Set the number of NOCB callback kthreads in
+			each group, which defaults to the square root
+			of the number of CPUs.	Larger numbers reduce
+			the wakeup overhead on the global grace-period
+			kthread, but increases that same overhead on
+			each group's NOCB grace-period kthread.
+
 	rcutree.rcu_kick_kthreads= [KNL]
 			Cause the grace-period kthread to get an extra
 			wake_up() if it sleeps three times longer than
@@ -4866,6 +4856,13 @@
 			This wake_up() will be accompanied by a
 			WARN_ONCE() splat and an ftrace_dump().
 
+	rcutree.rcu_resched_ns= [KNL]
+			Limit the time spend invoking a batch of RCU
+			callbacks to the specified number of nanoseconds.
+			By default, this limit is checked only once
+			every 32 callbacks in order to limit the pain
+			inflicted by local_clock() overhead.
+
 	rcutree.rcu_unlock_delay= [KNL]
 			In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
 			this specifies an rcu_read_unlock()-time delay
@@ -4880,6 +4877,16 @@
 			rcu_node tree with an eye towards determining
 			why a new grace period has not yet started.
 
+	rcutree.use_softirq=	[KNL]
+			If set to zero, move all RCU_SOFTIRQ processing to
+			per-CPU rcuc kthreads.  Defaults to a non-zero
+			value, meaning that RCU_SOFTIRQ is used by default.
+			Specify rcutree.use_softirq=0 to use rcuc kthreads.
+
+			But note that CONFIG_PREEMPT_RT=y kernels disable
+			this kernel boot parameter, forcibly setting it
+			to zero.
+
 	rcuscale.gp_async= [KNL]
 			Measure performance of asynchronous
 			grace-period primitives such as call_rcu().
@@ -5082,8 +5089,17 @@
 
 	rcutorture.stall_cpu_block= [KNL]
 			Sleep while stalling if set.  This will result
-			in warnings from preemptible RCU in addition
-			to any other stall-related activity.
+			in warnings from preemptible RCU in addition to
+			any other stall-related activity.  Note that
+			in kernels built with CONFIG_PREEMPTION=n and
+			CONFIG_PREEMPT_COUNT=y, this parameter will
+			cause the CPU to pass through a quiescent state.
+			Given CONFIG_PREEMPTION=n, this will suppress
+			RCU CPU stall warnings, but will instead result
+			in scheduling-while-atomic splats.
+
+			Use of this module parameter results in splats.
+
 
 	rcutorture.stall_cpu_holdoff= [KNL]
 			Time to wait (s) after boot before inducing stall.
diff --git a/Documentation/core-api/kernel-api.rst b/Documentation/core-api/kernel-api.rst
index 9b3f3e5f5a95..712e59ad32fa 100644
--- a/Documentation/core-api/kernel-api.rst
+++ b/Documentation/core-api/kernel-api.rst
@@ -412,3 +412,15 @@ Read-Copy Update (RCU)
 .. kernel-doc:: include/linux/rcu_sync.h
 
 .. kernel-doc:: kernel/rcu/sync.c
+
+.. kernel-doc:: kernel/rcu/tasks.h
+
+.. kernel-doc:: kernel/rcu/tree_stall.h
+
+.. kernel-doc:: include/linux/rcupdate_trace.h
+
+.. kernel-doc:: include/linux/rcupdate_wait.h
+
+.. kernel-doc:: include/linux/rcuref.h
+
+.. kernel-doc:: include/linux/rcutree.h