linux/Documentation/RCU/Design, branch master

rcu-tasks: Document that RCU Tasks Trace grace periods now imply RCU grace periods

2026-03-30T19:48:14Z

Now that RCU Tasks Trace is implemented in terms of SRCU-fast, the fact that each SRCU-fast grace period implies at least two RCU grace periods in turn means that each RCU Tasks Trace grace period implies at least two grace periods. This commit therefore updates the documentation accordingly. Reviewed-by: Frederic Weisbecker Reported-by: Alexei Starovoitov Signed-off-by: Paul E. McKenney Signed-off-by: Joel Fernandes

rcu: Update Requirements.rst for RCU Tasks Trace

2026-01-01T08:39:46Z

This commit updates the documentation to declare that RCU Tasks Trace is implemented as a thin wrapper around SRCU-fast. Signed-off-by: Paul E. McKenney Cc: Andrii Nakryiko Cc: Alexei Starovoitov Cc: Peter Zijlstra Cc: bpf@vger.kernel.org Reviewed-by: Joel Fernandes Signed-off-by: Boqun Feng

doc: Update for SRCU-fast definitions and initialization

2025-11-05T22:58:30Z

This commit documents the DEFINE_SRCU_FAST(), DEFINE_STATIC_SRCU_FAST(), and init_srcu_struct_fast() API members. Signed-off-by: Paul E. McKenney Cc: Mathieu Desnoyers Cc: Steven Rostedt Cc: Sebastian Andrzej Siewior Cc: Signed-off-by: Frederic Weisbecker

rcu: docs: Requirements.rst: Abide by conventions of kernel documentation

2025-08-20T18:51:28Z

Here is a list of conventions applied here: - Don't mark up function names, to be taken care of by the automarkup extension. Just say func(). - Instead of ".. code-block:: none", just say "::". - Mark inline literals by a pair of ``xxxx``. Don't use rust doc's dialect of `yyyy`. - Instead of emphasizing headings by **strong emphasis**, use sub-level title adornments, in this case "^^^^^^^^^^" and make them proper sub-sections under "Hotplug CPU". Signed-off-by: Akira Yokosawa Cc: Joel Fernandes Signed-off-by: Neeraj Upadhyay (AMD) Signed-off-by: Paul E. McKenney

rcu: Document concurrent quiescent state reporting for offline CPUs

2025-07-22T11:40:50Z

The synchronization of CPU offlining with GP initialization is confusing to put it mildly (rightfully so as the issue it deals with is complex). Recent discussions brought up a question -- what prevents the rcu_implicit_dyntick_qs() from warning about QS reports for offline CPUs (missing QS reports for offline CPUs causing indefinite hangs). QS reporting for now-offline CPUs should only happen from: - gp_init() - rcutree_cpu_report_dead() Add some documentation on this and refer to it from comments in the code explaining how QS reporting is not missed when these functions are concurrently running. I referred heavily to this post [1] about the need for the ofl_lock. [1] https://lore.kernel.org/all/20180924164443.GF4222@linux.ibm.com/ [ Applied paulmck feedback on moving documentation to Requirements.rst ] Link: https://lore.kernel.org/all/01b4d228-9416-43f8-a62e-124b92e8741a@paulmck-laptop/ Co-developed-by: "Paul E. McKenney" Signed-off-by: "Paul E. McKenney" Reviewed-by: Frederic Weisbecker Signed-off-by: Joel Fernandes Signed-off-by: Neeraj Upadhyay (AMD)

rcu: Document separation of rcu_state and rnp's gp_seq

2025-07-22T11:40:31Z

The details of this are subtle and was discussed recently. Add a quick-quiz about this and refer to it from the code, for more clarity. Reviewed-by: "Paul E. McKenney" Signed-off-by: Joel Fernandes Signed-off-by: Neeraj Upadhyay (AMD)

rcu: Document GP init vs hotplug-scan ordering requirements

2025-07-22T11:39:35Z

Add detailed comments explaining the critical ordering constraints during RCU grace period initialization, based on discussions with Frederic. Reviewed-by: "Paul E. McKenney" Co-developed-by: Frederic Weisbecker Signed-off-by: Frederic Weisbecker Signed-off-by: Joel Fernandes Signed-off-by: Neeraj Upadhyay (AMD)

Merge branches 'context_tracking.15.08.24a', 'csd.lock.15.08.24a', 'nocb.09.09.24a', 'rcutorture.14.08.24a', 'rcustall.09.09.24a', 'srcu.12.08.24a', 'rcu.tasks.14.08.24a', 'rcu_scaling_tests.15.08.24a', 'fixes.12.08.24a' and 'misc.11.08.24a' into next.09.09.24a

2024-09-08T18:39:47Z

rcu: Update stray documentation references to rcu_dynticks_eqs_{enter, exit}()

2024-08-15T16:00:43Z

rcu_dynticks_eqs_{enter, exit}() have been replaced by their context-tracking counterparts since commit: 171476775d32 ("context_tracking: Convert state to atomic_t") Update the stray documentation references. Signed-off-by: Valentin Schneider Reviewed-by: Frederic Weisbecker Signed-off-by: Neeraj Upadhyay

rcu: Rename rcu_implicit_dynticks_qs() into rcu_watching_snap_recheck()

2024-08-15T16:00:42Z

The context_tracking.state RCU_DYNTICKS subvariable has been renamed to RCU_WATCHING, drop the dyntick reference and update the name of this helper to express that it rechecks rdp->watching_snap after an earlier rcu_watching_snap_save(). Signed-off-by: Valentin Schneider Reviewed-by: Frederic Weisbecker Signed-off-by: Neeraj Upadhyay