Merge tag 'rcu.2024.07.12a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU updates from Paul McKenney:

 - Update Tasks RCU and Tasks Rude RCU description in Requirements.rst
   and clarify rcu_assign_pointer() and rcu_dereference() ordering
   properties

 - Add lockdep assertions for RCU readers, limit inline wakeups for
   callback-bypass synchronize_rcu(), add an
   rcutree.nohz_full_patience_delay to reduce nohz_full OS jitter, add
   Uladzislau Rezki as RCU maintainer, and fix a subtle
   callback-migration memory-ordering issue

 - Remove a number of redundant memory barriers

 - Remove unnecessary bypass-list lock-contention mitigation, use
   parking API instead of open-coded ad-hoc equivalent, and upgrade
   obsolete comments

 - Revert avoidance of a deadlock that can no longer occur and properly
   synchronize Tasks Trace RCU checking of runqueues

 - Add tests for handling of double-call_rcu() bug, add missing
   MODULE_DESCRIPTION, and add a script that histograms the number of
   calls to RCU updaters

 - Fill out SRCU polled-grace-period API

* tag 'rcu.2024.07.12a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (29 commits)
  rcu: Fix rcu_barrier() VS post CPUHP_TEARDOWN_CPU invocation
  rcu: Eliminate lockless accesses to rcu_sync->gp_count
  MAINTAINERS: Add Uladzislau Rezki as RCU maintainer
  rcu: Add rcutree.nohz_full_patience_delay to reduce nohz_full OS jitter
  rcu/exp: Remove redundant full memory barrier at the end of GP
  rcu: Remove full memory barrier on RCU stall printout
  rcu: Remove full memory barrier on boot time eqs sanity check
  rcu/exp: Remove superfluous full memory barrier upon first EQS snapshot
  rcu: Remove superfluous full memory barrier upon first EQS snapshot
  rcu: Remove full ordering on second EQS snapshot
  srcu: Fill out polled grace-period APIs
  srcu: Update cleanup_srcu_struct() comment
  srcu: Add NUM_ACTIVE_SRCU_POLL_OLDSTATE
  srcu: Disable interrupts directly in srcu_gp_end()
  rcu: Disable interrupts directly in rcu_gp_init()
  rcu/tree: Reduce wake up for synchronize_rcu() common case
  rcu/tasks: Fix stale task snaphot for Tasks Trace
  tools/rcu: Add rcu-updaters.sh script
  rcutorture: Add missing MODULE_DESCRIPTION() macros
  rcutorture: Fix rcu_torture_fwd_cb_cr() data race
  ...

1 files changed, 8 insertions, 0 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 27ec49af1bf2..fc01da74cf99 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5015,6 +5015,14 @@
 			the ->nocb_bypass queue.  The definition of "too
 			many" is supplied by this kernel boot parameter.
 
+	rcutree.nohz_full_patience_delay= [KNL]
+			On callback-offloaded (rcu_nocbs) CPUs, avoid
+			disturbing RCU unless the grace period has
+			reached the specified age in milliseconds.
+			Defaults to zero.  Large values will be capped
+			at five seconds.  All values will be rounded down
+			to the nearest value representable by jiffies.
+
 	rcutree.qhimark= [KNL]
 			Set threshold of queued RCU callbacks beyond which
 			batch limiting is disabled.