On Fri, Jan 24, 2025 at 12:48:12PM +0100, Uladzislau Rezki wrote:
> On Thu, Jan 23, 2025 at 01:52:57PM -0800, Paul E. McKenney wrote:
> > On Thu, Jan 23, 2025 at 07:58:28PM +0100, Uladzislau Rezki (Sony) wrote:
> > > Switch for using of get_state_synchronize_rcu_full() and
> > > poll_state_synchronize_rcu_full() pair for debug a normal
> > > synchronize_rcu() call.
> > >
> > > Just using "not" full APIs to identify if a grace period
> > > is passed or not might lead to a false kernel splat.
> > >
> > > Signed-off-by: Uladzislau Rezki (Sony) <ure...@gmail.com>
> > > ---
> > > include/linux/rcupdate_wait.h | 4 ++++
> > > kernel/rcu/tree.c | 8 +++-----
> > > 2 files changed, 7 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h
> > > index f9bed3d3f78d..a16fc2a9a7d7 100644
> > > --- a/include/linux/rcupdate_wait.h
> > > +++ b/include/linux/rcupdate_wait.h
> > > @@ -16,6 +16,10 @@
> > > struct rcu_synchronize {
> > > struct rcu_head head;
> > > struct completion completion;
> > > +#ifdef CONFIG_PROVE_RCU
> > > + /* This is for testing. */
> > > + struct rcu_gp_oldstate oldstate;
> > > +#endif
> > > };
> > > void wakeme_after_rcu(struct rcu_head *head);
> > >
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 2795d6b5109c..0ae90089ef09 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -1612,12 +1612,10 @@ static void rcu_sr_normal_complete(struct
> > > llist_node *node)
> > > {
> > > struct rcu_synchronize *rs = container_of(
> > > (struct rcu_head *) node, struct rcu_synchronize, head);
> > > - unsigned long oldstate = (unsigned long) rs->head.func;
> > >
> > > WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) &&
> > > - !poll_state_synchronize_rcu(oldstate),
> > > - "A full grace period is not passed yet: %lu",
> > > - rcu_seq_diff(get_state_synchronize_rcu(), oldstate));
> > > + !poll_state_synchronize_rcu_full(&rs->oldstate),
> > > + "A full grace period is not passed yet!\n");
> >
> > Looks good, but why not also continue printing out the required
> > grace-period sequence number? Yes, there would need to be helper
> > sprintf()-style functions to paper over the difference between Tiny RCU
> > and Tree RCU. ;-)
> >
> Uhh :) Do we have rcu_seq_diff() for a _full() API? Looks like not :)
>
> It contains both, rgos_norm and rgos_exp! Take a delta of both?
Why not? Maybe separate the two differences with a colon.
Or maybe make a variant of poll_state_synchronize_rcu_full() that take
a char* argument, which uses the same value for the check and the string
to be output.
Thanx, Paul
