linux-kernel - [PATCH v4 0/9] Implement RCU Tasks Trace in terms of SRCU for post-v4.19

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Message-ID: <b206b083-f611-43b6-993f-78ddbe315813@paulmck-laptop>
Date: Mon, 29 Dec 2025 11:10:55 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, kernel-team@...a.com, rostedt@...dmis.org
Subject: [PATCH v4 0/9] Implement RCU Tasks Trace in terms of SRCU for
 post-v4.19

Hello!

This v4 patch series re-implements RCU Tasks Trace in terms of SRCU-fast,
reducing the size of the Linux-kernel RCU implementation by several
hundred lines of code.  The patches are as follows:

1.	Re-implement RCU Tasks Trace in terms of SRCU-fast.

2.	context_tracking: Remove
	rcu_task_trace_heavyweight_{enter,exit}().

3.	Clean up after the SRCU-fastification of RCU Tasks Trace.

4.	Move rcu_tasks_trace_srcu_struct out of #ifdef
	CONFIG_TASKS_RCU_GENERIC.

5.	Add noinstr-fast rcu_read_{,un}lock_tasks_trace() APIs.

6.	Update Requirements.rst for RCU Tasks Trace.

7.	Deprecate rcu_read_{,un}lock_trace().

8.	Create an rcu_tasks_trace_expedite_current() function.

9.	Test rcu_tasks_trace_expedite_current().

Changes since v3:

o	Rebase onto v6.19-rc1.

o	Wait for arm64 per-CPU variable speedups to reach mainline.

https://lore.kernel.org/all/a1e505e4-931b-45cf-8ca7-337442aa598e@paulmck-laptop/#r

Changes since v2:

o	SRCU improvments not strictly related to RCU tasks trace have
	been moved out to a separate series.

o	Use the new DEFINE_SRCU_FAST().

https://lore.kernel.org/all/7fa58961-2dce-4e08-8174-1d1cc592210f@paulmck-laptop/

Changes since v1:

o	Consolidate RCU Tasks Trace cleanup patches per Alexei Starovoitov
	feedback.  This explains the decrease from 34 patches in v1 to
	only 21 in this v2 series.

o	While consolidating, consolidate the noinstr-fast patches and the
	DEFINE_SRCU_FAST()/init_srcu_struct_fast() patches.

o	Upgrade comments per Peter Zijlstra feedback.

o	Extract Tiny SRCU bug fix into its own commit per Andrii Nakryiko
	feedback.

o	Switch srcu_expedite_current() from preempt_disable() to
	migrate_disable() for PREEMPT_RT kernels per Zqiang feedback.

o	Apply tags.

https://lore.kernel.org/all/580ea2de-799a-4ddc-bde9-c16f3fb1e6e7@paulmck-laptop/

						Thanx, Paul

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

 b/Documentation/RCU/Design/Requirements/Requirements.rst |   12 
 b/Documentation/admin-guide/kernel-parameters.txt        |   15 
 b/include/linux/rcupdate.h                               |   31 
 b/include/linux/rcupdate_trace.h                         |  107 +-
 b/include/linux/sched.h                                  |    1 
 b/init/init_task.c                                       |    3 
 b/kernel/context_tracking.c                              |   20 
 b/kernel/fork.c                                          |    3 
 b/kernel/rcu/Kconfig                                     |   18 
 b/kernel/rcu/rcu.h                                       |    9 
 b/kernel/rcu/rcuscale.c                                  |    7 
 b/kernel/rcu/rcutorture.c                                |    2 
 b/kernel/rcu/tasks.h                                     |  621 ---------------
 b/scripts/checkpatch.pl                                  |    4 
 b/tools/testing/selftests/rcutorture/configs/rcu/TRACE01 |    1 
 b/tools/testing/selftests/rcutorture/configs/rcu/TRACE02 |    1 
 include/linux/rcupdate_trace.h                           |   81 +
 include/linux/sched.h                                    |    5 
 kernel/rcu/Kconfig                                       |   25 
 kernel/rcu/rcutorture.c                                  |    1 
 kernel/rcu/tasks.h                                       |  121 --
 21 files changed, 219 insertions(+), 869 deletions(-)