[PATCH 0/2] RCU API documentation updates

[PATCH 0/2] RCU API documentation updates

[Paul E. McKenney]

Hello!

This series updates RCU documentation to reflect RCU API additions:

1.	Update whatisRCU.rst for recent RCU API additions.

2.	Add RCU guards to checklist.rst.

						Thanx, Paul

------------------------------------------------------------------------

 checklist.rst |   27 +++++++---
 whatisRCU.rst |  150 +++++++++++++++++++++++++++++++++++++++++++++-------------
 2 files changed, 137 insertions(+), 40 deletions(-)

[PATCH RFC 1/2] doc: Update whatisRCU.rst for recent RCU API additions

[Paul E. McKenney]

Bring this file kicking and screaming into the year 2025!

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 Documentation/RCU/whatisRCU.rst | 150 +++++++++++++++++++++++++-------
 1 file changed, 118 insertions(+), 32 deletions(-)

diff --git a/Documentation/RCU/whatisRCU.rst b/Documentation/RCU/whatisRCU.rst
index be2eb6be16ece..6c69c20086e14 100644
--- a/Documentation/RCU/whatisRCU.rst
+++ b/Documentation/RCU/whatisRCU.rst
@@ -1021,32 +1021,41 @@ RCU list traversal::
 	list_entry_rcu
 	list_entry_lockless
 	list_first_entry_rcu
+	list_first_or_null_rcu
+	list_tail_rcu
 	list_next_rcu
+	list_next_or_null_rcu
 	list_for_each_entry_rcu
 	list_for_each_entry_continue_rcu
 	list_for_each_entry_from_rcu
-	list_first_or_null_rcu
-	list_next_or_null_rcu
+	list_for_each_entry_lockless
 	hlist_first_rcu
 	hlist_next_rcu
 	hlist_pprev_rcu
 	hlist_for_each_entry_rcu
+	hlist_for_each_entry_rcu_notrace
 	hlist_for_each_entry_rcu_bh
 	hlist_for_each_entry_from_rcu
 	hlist_for_each_entry_continue_rcu
 	hlist_for_each_entry_continue_rcu_bh
 	hlist_nulls_first_rcu
+	hlist_nulls_next_rcu
 	hlist_nulls_for_each_entry_rcu
+	hlist_nulls_for_each_entry_safe
 	hlist_bl_first_rcu
 	hlist_bl_for_each_entry_rcu
 
 RCU pointer/list update::
 
 	rcu_assign_pointer
+	rcu_replace_pointer
+	INIT_LIST_HEAD_RCU
 	list_add_rcu
 	list_add_tail_rcu
 	list_del_rcu
 	list_replace_rcu
+	list_splice_init_rcu
+	list_splice_tail_init_rcu
 	hlist_add_behind_rcu
 	hlist_add_before_rcu
 	hlist_add_head_rcu
@@ -1054,34 +1063,53 @@ RCU pointer/list update::
 	hlist_del_rcu
 	hlist_del_init_rcu
 	hlist_replace_rcu
-	list_splice_init_rcu
-	list_splice_tail_init_rcu
 	hlist_nulls_del_init_rcu
 	hlist_nulls_del_rcu
 	hlist_nulls_add_head_rcu
+	hlist_nulls_add_tail_rcu
+	hlist_nulls_add_fake
+	hlists_swap_heads_rcu
 	hlist_bl_add_head_rcu
-	hlist_bl_del_init_rcu
 	hlist_bl_del_rcu
 	hlist_bl_set_first_rcu
 
 RCU::
 
-	Critical sections	Grace period		Barrier
-
-	rcu_read_lock		synchronize_net		rcu_barrier
-	rcu_read_unlock		synchronize_rcu
-	rcu_dereference		synchronize_rcu_expedited
-	rcu_read_lock_held	call_rcu
-	rcu_dereference_check	kfree_rcu
-	rcu_dereference_protected
+	Critical sections		Grace period		Barrier
+
+	rcu_read_lock			synchronize_net		rcu_barrier
+	rcu_read_unlock			synchronize_rcu
+	guard(rcu)()			synchronize_rcu_expedited
+	scoped_guard(rcu)		synchronize_rcu_mult
+	rcu_dereference			call_rcu
+	rcu_dereference_check		call_rcu_hurry
+	rcu_dereference_protected	kfree_rcu
+	rcu_read_lock_held		kvfree_rcu
+	rcu_read_lock_any_held		kfree_rcu_mightsleep
+	rcu_pointer_handoff		cond_synchronize_rcu
+	unrcu_pointer			cond_synchronize_rcu_full
+					cond_synchronize_rcu_expedited
+					cond_synchronize_rcu_expedited_full
+					get_completed_synchronize_rcu
+					get_completed_synchronize_rcu_full
+					get_state_synchronize_rcu
+					get_state_synchronize_rcu_full
+					poll_state_synchronize_rcu
+					poll_state_synchronize_rcu_full
+					same_state_synchronize_rcu
+					same_state_synchronize_rcu_full
+					start_poll_synchronize_rcu
+					start_poll_synchronize_rcu_full
+					start_poll_synchronize_rcu_expedited
+					start_poll_synchronize_rcu_expedited_full
 
 bh::
 
 	Critical sections	Grace period		Barrier
 
-	rcu_read_lock_bh	call_rcu		rcu_barrier
-	rcu_read_unlock_bh	synchronize_rcu
-	[local_bh_disable]	synchronize_rcu_expedited
+	rcu_read_lock_bh	[Same as RCU]		[Same as RCU]
+	rcu_read_unlock_bh
+	[local_bh_disable]
 	[and friends]
 	rcu_dereference_bh
 	rcu_dereference_bh_check
@@ -1092,9 +1120,9 @@ sched::
 
 	Critical sections	Grace period		Barrier
 
-	rcu_read_lock_sched	call_rcu		rcu_barrier
-	rcu_read_unlock_sched	synchronize_rcu
-	[preempt_disable]	synchronize_rcu_expedited
+	rcu_read_lock_sched	[Same as RCU]		[Same as RCU]
+	rcu_read_unlock_sched
+	[preempt_disable]
 	[and friends]
 	rcu_read_lock_sched_notrace
 	rcu_read_unlock_sched_notrace
@@ -1104,46 +1132,104 @@ sched::
 	rcu_read_lock_sched_held
 
 
+RCU: Initialization/cleanup/ordering::
+
+	RCU_INIT_POINTER
+	RCU_INITIALIZER
+	RCU_POINTER_INITIALIZER
+	init_rcu_head
+	destroy_rcu_head
+	init_rcu_head_on_stack
+	destroy_rcu_head_on_stack
+	SLAB_TYPESAFE_BY_RCU
+
+
+RCU: Quiescents states and control::
+
+	cond_resched_tasks_rcu_qs
+	rcu_all_qs
+	rcu_softirq_qs_periodic
+	rcu_end_inkernel_boot
+	rcu_expedite_gp
+	rcu_gp_is_expedited
+	rcu_unexpedite_gp
+	rcu_cpu_stall_reset
+	rcu_head_after_call_rcu
+	rcu_is_watching
+
+
+RCU-sync primitive:
+
+	rcu_sync_is_idle
+	rcu_sync_init
+	rcu_sync_enter
+	rcu_sync_exit
+	rcu_sync_dtor
+
+
 RCU-Tasks::
 
-	Critical sections	Grace period		Barrier
+	Critical sections	Grace period			Barrier
 
-	N/A			call_rcu_tasks		rcu_barrier_tasks
+	N/A			call_rcu_tasks			rcu_barrier_tasks
 				synchronize_rcu_tasks
 
 
 RCU-Tasks-Rude::
 
-	Critical sections	Grace period		Barrier
+	Critical sections	Grace period			Barrier
 
-	N/A						N/A
-				synchronize_rcu_tasks_rude
+	N/A			synchronize_rcu_tasks_rude	rcu_barrier_tasks_rude
+				call_rcu_tasks_rude
 
 
 RCU-Tasks-Trace::
 
-	Critical sections	Grace period		Barrier
+	Critical sections	Grace period			Barrier
 
-	rcu_read_lock_trace	call_rcu_tasks_trace	rcu_barrier_tasks_trace
+	rcu_read_lock_trace	call_rcu_tasks_trace		rcu_barrier_tasks_trace
 	rcu_read_unlock_trace	synchronize_rcu_tasks_trace
+	guard(rcu_tasks_trace)()
+	scoped_guard(rcu_tasks_trace)
 
 
-SRCU::
+SRCU list traversal::
+	list_for_each_entry_srcu
+	hlist_for_each_entry_srcu
 
-	Critical sections	Grace period		Barrier
 
-	srcu_read_lock		call_srcu		srcu_barrier
-	srcu_read_unlock	synchronize_srcu
-	srcu_dereference	synchronize_srcu_expedited
+SRCU::
+
+	Critical sections		Grace period		Barrier
+
+	srcu_read_lock			call_srcu		srcu_barrier
+	srcu_read_unlock		synchronize_srcu
+	srcu_read_lock_fast		synchronize_srcu_expedited
+	srcu_read_unlock_fast		get_state_synchronize_srcu
+	srcu_read_lock_nmisafe		start_poll_synchronize_srcu
+	srcu_read_unlock_nmisafe	start_poll_synchronize_srcu_expedited
+	srcu_read_lock_notrace		poll_state_synchronize_srcu
+	srcu_read_unlock_notrace
+	srcu_down_read
+	srcu_up_read
+	srcu_down_read_fast
+	srcu_up_read_fast
+	guard(srcu)()
+	scoped_guard(srcu)
+	srcu_read_lock_held
+	srcu_dereference
 	srcu_dereference_check
+	srcu_dereference_notrace
 	srcu_read_lock_held
 
-SRCU: Initialization/cleanup::
+
+SRCU: Initialization/cleanup/ordering::
 
 	DEFINE_SRCU
 	DEFINE_STATIC_SRCU
 	init_srcu_struct
 	cleanup_srcu_struct
+	smp_mb__after_srcu_read_unlock
 
 All: lockdep-checked RCU utility APIs::
 
-- 
2.40.1

[PATCH RFC 2/2] doc: Add RCU guards to checklist.rst

[Paul E. McKenney]

Also note that RCU guards can be easier to use.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 Documentation/RCU/checklist.rst | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst
index 7de3e308f330f..c9bfb2b218e52 100644
--- a/Documentation/RCU/checklist.rst
+++ b/Documentation/RCU/checklist.rst
@@ -69,7 +69,13 @@ over a rather long period of time, but improvements are always welcome!
 	Explicit disabling of preemption (preempt_disable(), for example)
 	can serve as rcu_read_lock_sched(), but is less readable and
 	prevents lockdep from detecting locking issues.  Acquiring a
-	spinlock also enters an RCU read-side critical section.
+	raw spinlock also enters an RCU read-side critical section.
+
+	The guard(rcu)() and scoped_guard(rcu) primitives designate
+	the remainder of the current scope or the next statement,
+	respectively, as the RCU read-side critical section.  Use of
+	these guards can be less error-prone than rcu_read_lock(),
+	rcu_read_unlock(), and friends.
 
 	Please note that you *cannot* rely on code known to be built
 	only in non-preemptible kernels.  Such code can and will break,
@@ -405,9 +411,11 @@ over a rather long period of time, but improvements are always welcome!
 13.	Unlike most flavors of RCU, it *is* permissible to block in an
 	SRCU read-side critical section (demarked by srcu_read_lock()
 	and srcu_read_unlock()), hence the "SRCU": "sleepable RCU".
-	Please note that if you don't need to sleep in read-side critical
-	sections, you should be using RCU rather than SRCU, because RCU
-	is almost always faster and easier to use than is SRCU.
+	As with RCU, guard(srcu)() and scoped_guard(srcu) forms are
+	available, and often provide greater ease of use.  Please note
+	that if you don't need to sleep in read-side critical sections,
+	you should be using RCU rather than SRCU, because RCU is almost
+	always faster and easier to use than is SRCU.
 
 	Also unlike other forms of RCU, explicit initialization and
 	cleanup is required either at build time via DEFINE_SRCU()
@@ -443,10 +451,13 @@ over a rather long period of time, but improvements are always welcome!
 	real-time workloads than is synchronize_rcu_expedited().
 
 	It is also permissible to sleep in RCU Tasks Trace read-side
-	critical section, which are delimited by rcu_read_lock_trace() and
-	rcu_read_unlock_trace().  However, this is a specialized flavor
-	of RCU, and you should not use it without first checking with
-	its current users.  In most cases, you should instead use SRCU.
+	critical section, which are delimited by rcu_read_lock_trace()
+	and rcu_read_unlock_trace().  However, this is a specialized
+	flavor of RCU, and you should not use it without first checking
+	with its current users.  In most cases, you should instead
+	use SRCU.  As with RCU and SRCU, guard(rcu_tasks_trace)() and
+	scoped_guard(rcu_tasks_trace) are available, and often provide
+	greater ease of use.
 
 	Note that rcu_assign_pointer() relates to SRCU just as it does to
 	other forms of RCU, but instead of rcu_dereference() you should
-- 
2.40.1