Merge tag 'rcu.release.v6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux

Pull RCU updates from Neeraj Upadhyay:
 "Context tracking:
   - rename context tracking state related symbols and remove references
     to "dynticks" in various context tracking state variables and
     related helpers
   - force context_tracking_enabled_this_cpu() to be inlined to avoid
     leaving a noinstr section

  CSD lock:
   - enhance CSD-lock diagnostic reports
   - add an API to provide an indication of ongoing CSD-lock stall

  nocb:
   - update and simplify RCU nocb code to handle (de-)offloading of
     callbacks only for offline CPUs
   - fix RT throttling hrtimer being armed from offline CPU

  rcutorture:
   - remove redundant rcu_torture_ops get_gp_completed fields
   - add SRCU ->same_gp_state and ->get_comp_state functions
   - add generic test for NUM_ACTIVE_*RCU_POLL* for testing RCU and SRCU
     polled grace periods
   - add CFcommon.arch for arch-specific Kconfig options
   - print number of update types in rcu_torture_write_types()
   - add rcutree.nohz_full_patience_delay testing to the TREE07 scenario
   - add a stall_cpu_repeat module parameter to test repeated CPU stalls
   - add argument to limit number of CPUs a guest OS can use in
     torture.sh

  rcustall:
   - abbreviate RCU CPU stall warnings during CSD-lock stalls
   - Allow dump_cpu_task() to be called without disabling preemption
   - defer printing stall-warning backtrace when holding rcu_node lock

  srcu:
   - make SRCU gp seq wrap-around faster
   - add KCSAN checks for concurrent updates to ->srcu_n_exp_nodelay and
     ->reschedule_count which are used in heuristics governing
     auto-expediting of normal SRCU grace periods and
     grace-period-state-machine delays
   - mark idle SRCU-barrier callbacks to help identify stuck
     SRCU-barrier callback

  rcu tasks:
   - remove RCU Tasks Rude asynchronous APIs as they are no longer used
   - stop testing RCU Tasks Rude asynchronous APIs
   - fix access to non-existent percpu regions
   - check processor-ID assumptions during chosen CPU calculation for
     callback enqueuing
   - update description of rtp->tasks_gp_seq grace-period sequence
     number
   - add rcu_barrier_cb_is_done() to identify whether a given
     rcu_barrier callback is stuck
   - mark idle Tasks-RCU-barrier callbacks
   - add *torture_stats_print() functions to print detailed diagnostics
     for Tasks-RCU variants
   - capture start time of rcu_barrier_tasks*() operation to help
     distinguish a hung barrier operation from a long series of barrier
     operations

  refscale:
   - add a TINY scenario to support tests of Tiny RCU and Tiny
     SRCU
   - optimize process_durations() operation

  rcuscale:
   - dump stacks of stalled rcu_scale_writer() instances and
     grace-period statistics when rcu_scale_writer() stalls
   - mark idle RCU-barrier callbacks to identify stuck RCU-barrier
     callbacks
   - print detailed grace-period and barrier diagnostics on
     rcu_scale_writer() hangs for Tasks-RCU variants
   - warn if async module parameter is specified for RCU implementations
     that do not have async primitives such as RCU Tasks Rude
   - make all writer tasks report upon hang
   - tolerate repeated GFP_KERNEL failure in rcu_scale_writer()
   - use special allocator for rcu_scale_writer()
   - NULL out top-level pointers to heap memory to avoid double-free
     bugs on modprobe failures
   - maintain per-task instead of per-CPU callbacks count to avoid any
     issues with migration of either tasks or callbacks
   - constify struct ref_scale_ops

  Fixes:
   - use system_unbound_wq for kfree_rcu work to avoid disturbing
     isolated CPUs

  Misc:
   - warn on unexpected rcu_state.srs_done_tail state
   - better define "atomic" for list_replace_rcu() and
     hlist_replace_rcu() routines
   - annotate struct kvfree_rcu_bulk_data with __counted_by()"

* tag 'rcu.release.v6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (90 commits)
  rcu: Defer printing stall-warning backtrace when holding rcu_node lock
  rcu/nocb: Remove superfluous memory barrier after bypass enqueue
  rcu/nocb: Conditionally wake up rcuo if not already waiting on GP
  rcu/nocb: Fix RT throttling hrtimer armed from offline CPU
  rcu/nocb: Simplify (de-)offloading state machine
  context_tracking: Tag context_tracking_enabled_this_cpu() __always_inline
  context_tracking, rcu: Rename rcu_dyntick trace event into rcu_watching
  rcu: Update stray documentation references to rcu_dynticks_eqs_{enter, exit}()
  rcu: Rename rcu_momentary_dyntick_idle() into rcu_momentary_eqs()
  rcu: Rename rcu_implicit_dynticks_qs() into rcu_watching_snap_recheck()
  rcu: Rename dyntick_save_progress_counter() into rcu_watching_snap_save()
  rcu: Rename struct rcu_data .exp_dynticks_snap into .exp_watching_snap
  rcu: Rename struct rcu_data .dynticks_snap into .watching_snap
  rcu: Rename rcu_dynticks_zero_in_eqs() into rcu_watching_zero_in_eqs()
  rcu: Rename rcu_dynticks_in_eqs_since() into rcu_watching_snap_stopped_since()
  rcu: Rename rcu_dynticks_in_eqs() into rcu_watching_snap_in_eqs()
  rcu: Rename rcu_dynticks_eqs_online() into rcu_watching_online()
  context_tracking, rcu: Rename rcu_dynticks_curr_cpu_in_eqs() into rcu_is_watching_curr_cpu()
  context_tracking, rcu: Rename rcu_dynticks_task*() into rcu_task*()
  refscale: Constify struct ref_scale_ops
  ...

Author: torvalds

Documentation/RCU/Design/Data-Structures/Data-Structures.rst

@@ -921,10 +921,10 @@ This portion of the ``rcu_data`` structure is declared as follows:
 
 ::
 
-     1   int dynticks_snap;
+     1   int watching_snap;
      2   unsigned long dynticks_fqs;
 
-The ``->dynticks_snap`` field is used to take a snapshot of the
+The ``->watching_snap`` field is used to take a snapshot of the
 corresponding CPU's dyntick-idle state when forcing quiescent states,
 and is therefore accessed from other CPUs. Finally, the
 ``->dynticks_fqs`` field is used to count the number of times this CPU
@@ -935,8 +935,8 @@ This portion of the rcu_data structure is declared as follows:
 
 ::
 
-     1   long dynticks_nesting;
-     2   long dynticks_nmi_nesting;
+     1   long nesting;
+     2   long nmi_nesting;
      3   atomic_t dynticks;
      4   bool rcu_need_heavy_qs;
      5   bool rcu_urgent_qs;
@@ -945,27 +945,27 @@ These fields in the rcu_data structure maintain the per-CPU dyntick-idle
 state for the corresponding CPU. The fields may be accessed only from
 the corresponding CPU (and from tracing) unless otherwise stated.
 
-The ``->dynticks_nesting`` field counts the nesting depth of process
+The ``->nesting`` field counts the nesting depth of process
 execution, so that in normal circumstances this counter has value zero
 or one. NMIs, irqs, and tracers are counted by the
-``->dynticks_nmi_nesting`` field. Because NMIs cannot be masked, changes
+``->nmi_nesting`` field. Because NMIs cannot be masked, changes
 to this variable have to be undertaken carefully using an algorithm
 provided by Andy Lutomirski. The initial transition from idle adds one,
 and nested transitions add two, so that a nesting level of five is
-represented by a ``->dynticks_nmi_nesting`` value of nine. This counter
+represented by a ``->nmi_nesting`` value of nine. This counter
 can therefore be thought of as counting the number of reasons why this
 CPU cannot be permitted to enter dyntick-idle mode, aside from
 process-level transitions.
 
 However, it turns out that when running in non-idle kernel context, the
 Linux kernel is fully capable of entering interrupt handlers that never
 exit and perhaps also vice versa. Therefore, whenever the
-``->dynticks_nesting`` field is incremented up from zero, the
-``->dynticks_nmi_nesting`` field is set to a large positive number, and
-whenever the ``->dynticks_nesting`` field is decremented down to zero,
-the ``->dynticks_nmi_nesting`` field is set to zero. Assuming that
+``->nesting`` field is incremented up from zero, the
+``->nmi_nesting`` field is set to a large positive number, and
+whenever the ``->nesting`` field is decremented down to zero,
+the ``->nmi_nesting`` field is set to zero. Assuming that
 the number of misnested interrupts is not sufficient to overflow the
-counter, this approach corrects the ``->dynticks_nmi_nesting`` field
+counter, this approach corrects the ``->nmi_nesting`` field
 every time the corresponding CPU enters the idle loop from process
 context.
 
@@ -992,8 +992,8 @@ code.
 +-----------------------------------------------------------------------+
 | **Quick Quiz**:                                                       |
 +-----------------------------------------------------------------------+
-| Why not simply combine the ``->dynticks_nesting`` and                 |
-| ``->dynticks_nmi_nesting`` counters into a single counter that just   |
+| Why not simply combine the ``->nesting`` and                          |
+| ``->nmi_nesting`` counters into a single counter that just            |
 | counts the number of reasons that the corresponding CPU is non-idle?  |
 +-----------------------------------------------------------------------+
 | **Answer**:                                                           |

Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst

@@ -147,10 +147,10 @@ RCU read-side critical sections preceding and following the current
 idle sojourn.
 This case is handled by calls to the strongly ordered
 ``atomic_add_return()`` read-modify-write atomic operation that
-is invoked within ``rcu_dynticks_eqs_enter()`` at idle-entry
-time and within ``rcu_dynticks_eqs_exit()`` at idle-exit time.
-The grace-period kthread invokes first ``ct_dynticks_cpu_acquire()``
-(preceded by a full memory barrier) and ``rcu_dynticks_in_eqs_since()``
+is invoked within ``ct_kernel_exit_state()`` at idle-entry
+time and within ``ct_kernel_enter_state()`` at idle-exit time.
+The grace-period kthread invokes first ``ct_rcu_watching_cpu_acquire()``
+(preceded by a full memory barrier) and ``rcu_watching_snap_stopped_since()``
 (both of which rely on acquire semantics) to detect idle CPUs.
 
 +-----------------------------------------------------------------------+

Documentation/RCU/Design/Memory-Ordering/TreeRCU-dyntick.svg

@@ -2649,8 +2649,7 @@ those that are idle from RCU's perspective) and then Tasks Rude RCU can
 be removed from the kernel.
 
 The tasks-rude-RCU API is also reader-marking-free and thus quite compact,
-consisting of call_rcu_tasks_rude(), synchronize_rcu_tasks_rude(),
-and rcu_barrier_tasks_rude().
+consisting solely of synchronize_rcu_tasks_rude().
 
 Tasks Trace RCU
 ~~~~~~~~~~~~~~~

Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg

@@ -194,14 +194,13 @@ over a rather long period of time, but improvements are always welcome!
 		when publicizing a pointer to a structure that can
 		be traversed by an RCU read-side critical section.
 
-5.	If any of call_rcu(), call_srcu(), call_rcu_tasks(),
-	call_rcu_tasks_rude(), or call_rcu_tasks_trace() is used,
-	the callback function may be invoked from softirq context,
-	and in any case with bottom halves disabled.  In particular,
-	this callback function cannot block.  If you need the callback
-	to block, run that code in a workqueue handler scheduled from
-	the callback.  The queue_rcu_work() function does this for you
-	in the case of call_rcu().
+5.	If any of call_rcu(), call_srcu(), call_rcu_tasks(), or
+	call_rcu_tasks_trace() is used, the callback function may be
+	invoked from softirq context, and in any case with bottom halves
+	disabled.  In particular, this callback function cannot block.
+	If you need the callback to block, run that code in a workqueue
+	handler scheduled from the callback.  The queue_rcu_work()
+	function does this for you in the case of call_rcu().
 
 6.	Since synchronize_rcu() can block, it cannot be called
 	from any sort of irq context.  The same rule applies
@@ -254,10 +253,10 @@ over a rather long period of time, but improvements are always welcome!
 		corresponding readers must use rcu_read_lock_trace()
 		and rcu_read_unlock_trace().
 
-	c.	If an updater uses call_rcu_tasks_rude() or
-		synchronize_rcu_tasks_rude(), then the corresponding
-		readers must use anything that disables preemption,
-		for example, preempt_disable() and preempt_enable().
+	c.	If an updater uses synchronize_rcu_tasks_rude(),
+		then the corresponding readers must use anything that
+		disables preemption, for example, preempt_disable()
+		and preempt_enable().
 
 	Mixing things up will result in confusion and broken kernels, and
 	has even resulted in an exploitable security issue.  Therefore,
@@ -326,11 +325,9 @@ over a rather long period of time, but improvements are always welcome!
 	d.	Periodically invoke rcu_barrier(), permitting a limited
 		number of updates per grace period.
 
-	The same cautions apply to call_srcu(), call_rcu_tasks(),
-	call_rcu_tasks_rude(), and call_rcu_tasks_trace().  This is
-	why there is an srcu_barrier(), rcu_barrier_tasks(),
-	rcu_barrier_tasks_rude(), and rcu_barrier_tasks_rude(),
-	respectively.
+	The same cautions apply to call_srcu(), call_rcu_tasks(), and
+	call_rcu_tasks_trace().  This is why there is an srcu_barrier(),
+	rcu_barrier_tasks(), and rcu_barrier_tasks_trace(), respectively.
 
 	Note that although these primitives do take action to avoid
 	memory exhaustion when any given CPU has too many callbacks,
@@ -383,17 +380,17 @@ over a rather long period of time, but improvements are always welcome!
 	must use whatever locking or other synchronization is required
 	to safely access and/or modify that data structure.
 
-	Do not assume that RCU callbacks will be executed on
-	the same CPU that executed the corresponding call_rcu(),
-	call_srcu(), call_rcu_tasks(), call_rcu_tasks_rude(), or
-	call_rcu_tasks_trace().  For example, if a given CPU goes offline
-	while having an RCU callback pending, then that RCU callback
-	will execute on some surviving CPU.  (If this was not the case,
-	a self-spawning RCU callback would prevent the victim CPU from
-	ever going offline.)  Furthermore, CPUs designated by rcu_nocbs=
-	might well *always* have their RCU callbacks executed on some
-	other CPUs, in fact, for some  real-time workloads, this is the
-	whole point of using the rcu_nocbs= kernel boot parameter.
+	Do not assume that RCU callbacks will be executed on the same
+	CPU that executed the corresponding call_rcu(), call_srcu(),
+	call_rcu_tasks(), or call_rcu_tasks_trace().  For example, if
+	a given CPU goes offline while having an RCU callback pending,
+	then that RCU callback will execute on some surviving CPU.
+	(If this was not the case, a self-spawning RCU callback would
+	prevent the victim CPU from ever going offline.)  Furthermore,
+	CPUs designated by rcu_nocbs= might well *always* have their
+	RCU callbacks executed on some other CPUs, in fact, for some
+	real-time workloads, this is the whole point of using the
+	rcu_nocbs= kernel boot parameter.
 
 	In addition, do not assume that callbacks queued in a given order
 	will be invoked in that order, even if they all are queued on the
@@ -507,9 +504,9 @@ over a rather long period of time, but improvements are always welcome!
 	These debugging aids can help you find problems that are
 	otherwise extremely difficult to spot.
 
-17.	If you pass a callback function defined within a module to one of
-	call_rcu(), call_srcu(), call_rcu_tasks(), call_rcu_tasks_rude(),
-	or call_rcu_tasks_trace(), then it is necessary to wait for all
+17.	If you pass a callback function defined within a module
+	to one of call_rcu(), call_srcu(), call_rcu_tasks(), or
+	call_rcu_tasks_trace(), then it is necessary to wait for all
 	pending callbacks to be invoked before unloading that module.
 	Note that it is absolutely *not* sufficient to wait for a grace
 	period!  For example, synchronize_rcu() implementation is *not*
@@ -522,7 +519,6 @@ over a rather long period of time, but improvements are always welcome!
 	-	call_rcu() -> rcu_barrier()
 	-	call_srcu() -> srcu_barrier()
 	-	call_rcu_tasks() -> rcu_barrier_tasks()
-	-	call_rcu_tasks_rude() -> rcu_barrier_tasks_rude()
 	-	call_rcu_tasks_trace() -> rcu_barrier_tasks_trace()
 
 	However, these barrier functions are absolutely *not* guaranteed
@@ -539,7 +535,6 @@ over a rather long period of time, but improvements are always welcome!
 	-	Either synchronize_srcu() or synchronize_srcu_expedited(),
 		together with and srcu_barrier()
 	-	synchronize_rcu_tasks() and rcu_barrier_tasks()
-	-	synchronize_tasks_rude() and rcu_barrier_tasks_rude()
 	-	synchronize_tasks_trace() and rcu_barrier_tasks_trace()
 
 	If necessary, you can use something like workqueues to execute

Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg

@@ -1103,7 +1103,7 @@ RCU-Tasks-Rude::
 
 	Critical sections	Grace period		Barrier
 
-	N/A			call_rcu_tasks_rude	rcu_barrier_tasks_rude
+	N/A						N/A
 				synchronize_rcu_tasks_rude
 
 

Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg

@@ -4969,6 +4969,10 @@
 			Set maximum number of finished RCU callbacks to
 			process in one batch.
 
+	rcutree.csd_lock_suppress_rcu_stall=	[KNL]
+			Do only a one-line RCU CPU stall warning when
+			there is an ongoing too-long CSD-lock wait.
+
 	rcutree.do_rcu_barrier=	[KNL]
 			Request a call to rcu_barrier().  This is
 			throttled so that userspace tests can safely
@@ -5416,7 +5420,13 @@
 			Time to wait (s) after boot before inducing stall.
 
 	rcutorture.stall_cpu_irqsoff= [KNL]
-			Disable interrupts while stalling if set.
+			Disable interrupts while stalling if set, but only
+			on the first stall in the set.
+
+	rcutorture.stall_cpu_repeat= [KNL]
+			Number of times to repeat the stall sequence,
+			so that rcutorture.stall_cpu_repeat=3 will result
+			in four stall sequences.
 
 	rcutorture.stall_gp_kthread= [KNL]
 			Duration (s) of forced sleep within RCU
@@ -5604,14 +5614,6 @@
 			of zero will disable batching.	Batching is
 			always disabled for synchronize_rcu_tasks().
 
-	rcupdate.rcu_tasks_rude_lazy_ms= [KNL]
-			Set timeout in milliseconds RCU Tasks
-			Rude asynchronous callback batching for
-			call_rcu_tasks_rude().	A negative value
-			will take the default.	A value of zero will
-			disable batching.  Batching is always disabled
-			for synchronize_rcu_tasks_rude().
-
 	rcupdate.rcu_tasks_trace_lazy_ms= [KNL]
 			Set timeout in milliseconds RCU Tasks
 			Trace asynchronous callback batching for