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

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Message-ID: <20251230231911.GA2605197@joelbox2>
Date: Tue, 30 Dec 2025 18:19:11 -0500
From: Joel Fernandes <joelagnelf@...dia.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	rostedt@...dmis.org
Subject: Re: [PATCH v4 0/9] Implement RCU Tasks Trace in terms of SRCU for
 post-v4.19

On Mon, Dec 29, 2025 at 11:10:55AM -0800, Paul E. McKenney wrote:
> 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(-)

Reviewed-by: Joel Fernandes <joelagnelf@...dia.com>

thanks