On Fri, Oct 14, 2022 at 12:20:19PM +0800, Hou Tao wrote:
> Hi,
>
> On 10/14/2022 3:00 AM, Paul E. McKenney wrote:
> > On Thu, Oct 13, 2022 at 09:25:31AM +0800, Hou Tao wrote:
> >> Hi,
> >>
> >> On 10/13/2022 12:11 AM, Paul E. McKenney wrote:
> >>> On Wed, Oct 12, 2022 at 05:26:26PM +0800, Hou Tao wrote:
> SNIP
> >>> How about if I produce a patch for rcu_trace_implies_rcu_gp() and let
> >>> you carry it with your series? That way I don't have an unused function
> >>> in -rcu and you don't have to wait for me to send it upstream?
> >> Sound reasonable to me. Also thanks for your suggestions.
> > Here you go! Thoughts?
>
> It looks great and thanks for it.
Very good! I will carry it in -rcu for some time, so please let me know
when/if you pull it into a series.
Thanx, Paul
> > ------------------------------------------------------------------------
> >
> > commit 2eac2f7a9a6d8921e8084a6acdffa595e99dbd17
> > Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > Date: Thu Oct 13 11:54:13 2022 -0700
> >
> > rcu-tasks: Provide rcu_trace_implies_rcu_gp()
> >
> > 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.
> > This commit therefore creates an rcu_trace_implies_rcu_gp() that currently
> > returns true to codify this accident. Code relying on this accident
> > must call this function to verify that this accident is still happening.
> >
> > Reported-by: Hou Tao <houtao@xxxxxxxxxxxxxxx>
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> > Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
> >
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index 08605ce7379d7..8822f06e4b40c 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -240,6 +240,18 @@ static inline void exit_tasks_rcu_start(void) { }
> > static inline void exit_tasks_rcu_finish(void) { }
> > #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
> >
> > +/**
> > + * 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!
> > + */
> > +static inline bool rcu_trace_implies_rcu_gp(void) { return true; }
> > +
> > /**
> > * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
> > *
> > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> > index b0b885e071fa8..fe9840d90e960 100644
> > --- a/kernel/rcu/tasks.h
> > +++ b/kernel/rcu/tasks.h
> > @@ -1535,6 +1535,8 @@ static void rcu_tasks_trace_postscan(struct list_head *hop)
> > {
> > // Wait for late-stage exiting tasks to finish exiting.
> > // These might have passed the call to exit_tasks_rcu_finish().
> > +
> > + // If you remove the following line, update rcu_trace_implies_rcu_gp()!!!
> > synchronize_rcu();
> > // Any tasks that exit after this point will set
> > // TRC_NEED_QS_CHECKED in ->trc_reader_special.b.need_qs.
>
