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

[Boqun Feng <boqun.feng@gmail.com>]

On Tue, Dec 30, 2025 at 06:19:11PM -0500, Joel Fernandes wrote:
> 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@nvidia.com>
> 

Queued, thank you both!

Regards,
Boqun

> thanks
> 
>