* [PATCH RFC 1/2] doc: Update whatisRCU.rst for recent RCU API additions
2025-07-16 0:45 [PATCH 0/2] RCU API documentation updates Paul E. McKenney
@ 2025-07-16 0:45 ` Paul E. McKenney
2025-07-16 0:45 ` [PATCH RFC 2/2] doc: Add RCU guards to checklist.rst Paul E. McKenney
1 sibling, 0 replies; 3+ messages in thread
From: Paul E. McKenney @ 2025-07-16 0:45 UTC (permalink / raw)
To: rcu; +Cc: linux-kernel, kernel-team, rostedt, 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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [PATCH RFC 2/2] doc: Add RCU guards to checklist.rst
2025-07-16 0:45 [PATCH 0/2] RCU API documentation updates Paul E. McKenney
2025-07-16 0:45 ` [PATCH RFC 1/2] doc: Update whatisRCU.rst for recent RCU API additions Paul E. McKenney
@ 2025-07-16 0:45 ` Paul E. McKenney
1 sibling, 0 replies; 3+ messages in thread
From: Paul E. McKenney @ 2025-07-16 0:45 UTC (permalink / raw)
To: rcu; +Cc: linux-kernel, kernel-team, rostedt, 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
^ permalink raw reply related [flat|nested] 3+ messages in thread