Merge tag 'rcu.release.v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux

Pull RCU updates from Frederic Weisbecker:
 "SRCU:

   - Introduction of the new SRCU-lite flavour with a new pair of
     srcu_read_[un]lock_lite() APIs. In practice the read side using
     this flavour becomes lighter by removing a full memory barrier on
     LOCK and a full memory barrier on UNLOCK. This comes at the expense
     of a higher latency write side with two (in the best case of a
     snaphot of unused read-sides) or more RCU grace periods on the
     update side which now assumes by itself the whole full ordering
     guarantee against the LOCK/UNLOCK counters on both indexes, along
     with the accesses performed inside.

     Uretprobes is a known potential user.

     Note this doesn't replace the default normal flavour of SRCU which
     still behaves the same as usual.

   - Add testing of SRCU-lite through rcutorture and rcuscale

   - Various cleanups on the way.

  Fixes:

   - Allow short-circuiting RCU-TASKS-RUDE grace periods on
     architectures that have sane noinstr boundaries forbidding tracing
     on low-level idle and kernel entry code. RCU-TASKS is enough on
     such configurations because it involves an RCU grace period that
     waits for all idle tasks to either schedule out voluntarily or
     enter into RCU unwatched noinstr code.

   - Allow and test start_poll_synchronize_rcu() with IRQs disabled.

   - Mention rcuog kthreads in relevant documentation and Kconfig help

   - Various fixes and consolidations

  rcutorture:

   - Add --no-affinity on tools to leave the affinity setting of guests
     up to the user.

   - Add guest_os_delay parameter to rcuscale for better warm-up
     control.

   - Fix and improve some rcuscale error handling.

   - Various cleanups and fixes

  stall:

   - Remove dead code

   - Stop dumping tasks if a stalled grace period eventually ended
     midway as that only produces confusing output.

   - Optimize detection of stalling CPUs and avoid useless node locking
     otherwise.

  NOCB:

   - Fix rcu_barrier() hang due to a race against callbacks
     deoffloading. This is not yet used, except by rcutorture, and waits
     for its promised cpusets interface.

   - Remove leftover function declaration"

* tag 'rcu.release.v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (42 commits)
  rcuscale: Remove redundant WARN_ON_ONCE() splat
  rcuscale: Do a proper cleanup if kfree_scale_init() fails
  srcu: Unconditionally record srcu_read_lock_lite() in ->srcu_reader_flavor
  srcu: Check for srcu_read_lock_lite() across all CPUs
  srcu: Remove smp_mb() from srcu_read_unlock_lite()
  rcutorture: Avoid printing cpu=-1 for no-fault RCU boost failure
  rcuscale: Add guest_os_delay module parameter
  refscale: Correct affinity check
  torture: Add --no-affinity parameter to kvm.sh
  rcu/nocb: Fix missed RCU barrier on deoffloading
  rcu/kvfree: Fix data-race in __mod_timer / kvfree_call_rcu
  rcu/srcutiny: don't return before reenabling preemption
  rcu-tasks: Remove open-coded one-byte cmpxchg() emulation
  doc: Remove kernel-parameters.txt entry for rcutorture.read_exit
  rcutorture: Test start-poll primitives with interrupts disabled
  rcu: Permit start_poll_synchronize_rcu*() with interrupts disabled
  rcu: Allow short-circuiting of synchronize_rcu_tasks_rude()
  doc: Add rcuog kthreads to kernel-per-CPU-kthreads.rst
  rcu: Add rcuog kthreads to RCU_NOCB_CPU help text
  rcu: Use the BITS_PER_LONG macro
  ...

3 files changed, 10 insertions, 7 deletions

diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst
index ca7b7cd806a1..30080ff6f406 100644
--- a/Documentation/RCU/stallwarn.rst
+++ b/Documentation/RCU/stallwarn.rst
@@ -249,7 +249,7 @@ ticks this GP)" indicates that this CPU has not taken any scheduling-clock
 interrupts during the current stalled grace period.
 
 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
+The hex number before the first "/" is the low-order 16 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
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f2875484795a..7e1315ee0507 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5415,11 +5415,6 @@
 			Set time (jiffies) between CPU-hotplug operations,
 			or zero to disable CPU-hotplug testing.
 
-	rcutorture.read_exit= [KNL]
-			Set the number of read-then-exit kthreads used
-			to test the interaction of RCU updaters and
-			task-exit processing.
-
 	rcutorture.read_exit_burst= [KNL]
 			The number of times in a given read-then-exit
 			episode that a set of read-then-exit kthreads
@@ -5429,6 +5424,14 @@
 			The delay, in seconds, between successive
 			read-then-exit testing episodes.
 
+	rcutorture.reader_flavor= [KNL]
+			A bit mask indicating which readers to use.
+			If there is more than one bit set, the readers
+			are entered from low-order bit up, and are
+			exited in the opposite order.  For SRCU, the
+			0x1 bit is normal readers, 0x2 NMI-safe readers,
+			and 0x4 light-weight readers.
+
 	rcutorture.shuffle_interval= [KNL]
 			Set task-shuffle interval (s).  Shuffling tasks
 			allows some CPUs to go into dyntick-idle mode
diff --git a/Documentation/admin-guide/kernel-per-CPU-kthreads.rst b/Documentation/admin-guide/kernel-per-CPU-kthreads.rst
index b6aeae3327ce..ea7fa2a8bbf0 100644
--- a/Documentation/admin-guide/kernel-per-CPU-kthreads.rst
+++ b/Documentation/admin-guide/kernel-per-CPU-kthreads.rst
@@ -315,7 +315,7 @@ To reduce its OS jitter, do at least one of the following:
 	to do.
 
 Name:
-  rcuop/%d and rcuos/%d
+  rcuop/%d, rcuos/%d, and rcuog/%d
 
 Purpose:
   Offload RCU callbacks from the corresponding CPU.