Le Tue, Mar 17, 2026 at 05:22:11PM -0400, Joel Fernandes a écrit : > From: "Paul E. McKenney" <[email protected]> > > 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
two or one? AFAIU srcu_readers_active_idx_check() it's only one? > in turn means that each RCU Tasks Trace grace period implies at least > two grace periods. This commit therefore updates the documentation > accordingly. > > Reported-by: Alexei Starovoitov <[email protected]> > Signed-off-by: Paul E. McKenney <[email protected]> > Signed-off-by: Joel Fernandes <[email protected]> > --- > Documentation/RCU/Design/Requirements/Requirements.rst | 7 +++++++ > include/linux/rcupdate.h | 9 +++------ > 2 files changed, 10 insertions(+), 6 deletions(-) > > diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst > b/Documentation/RCU/Design/Requirements/Requirements.rst > index b5cdbba3ec2e..4d886e7c7a95 100644 > --- a/Documentation/RCU/Design/Requirements/Requirements.rst > +++ b/Documentation/RCU/Design/Requirements/Requirements.rst > @@ -2787,6 +2787,13 @@ which avoids the read-side memory barriers, at least > for architectures > that apply noinstr to kernel entry/exit code (or that build with > ``CONFIG_TASKS_TRACE_RCU_NO_MB=y``. > > +Now that the implementation is based on SRCU-fast, a call > +to synchronize_rcu_tasks_trace() implies at least one call to > +synchronize_rcu(), that is, every Tasks Trace RCU grace period contains > +at least one plain vanilla RCU grace period. Should there ever > +be a synchronize_rcu_tasks_trace_expedited(), this guarantee would > +*not* necessarily apply to this hypothetical API member. > + > The tasks-trace-RCU API is also reasonably compact, > consisting of rcu_read_lock_trace(), rcu_read_unlock_trace(), > rcu_read_lock_trace_held(), call_rcu_tasks_trace(), > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 04f3f86a4145..18a85c30fd4f 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -208,12 +208,9 @@ static inline void exit_tasks_rcu_finish(void) { } > /** > * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an > RCU grace period? > * > - * As an accident of implementation, an RCU Tasks Trace grace period also > - * acts as an RCU grace period. However, this could change at any time. > - * Code relying on this accident must call this function to verify that > - * this accident is still happening. > - * > - * You have been warned! > + * Now that RCU Tasks Trace is implemented in terms of SRCU-fast, a > + * call to synchronize_rcu_tasks_trace() is guaranteed to imply at least > + * one call to synchronize_rcu(). > */ > static inline bool rcu_trace_implies_rcu_gp(void) { return true; } I guess the plan is to remote that function? Other than that: Reviewed-by: Frederic Weisbecker <[email protected]> > > -- > 2.34.1 > -- Frederic Weisbecker SUSE Labs
