On Tue, Sep 1, 2026 at 11:10 AM Paul E. McKenney <[email protected]> wrote: > > On Tue, Sep 01, 2026 at 10:00:24AM +0800, KunWu Chan wrote: > > On Tue, Sep 1, 2026 at 9:04 AM Paul E. McKenney <[email protected]> wrote: > > > > > > On Mon, Aug 31, 2026 at 03:49:37PM +0800, Kunwu Chan wrote: > > > > From: Kunwu Chan <[email protected]> > > > > > > > > Add atomic SRCU operation checks and the associated state to Tiny > > > > SRCU. > > > > > > > > An atomic SRCU domain does not use the normal SRCU callback and > > > > grace-period machinery. In particular, a callback queued with > > > > call_srcu() would never be processed. Use WARN_ON_ONCE() to reject > > > > call_srcu() and srcu_barrier() on atomic SRCU domains. > > > > > > > > For synchronize_srcu(), redirect atomic SRCU domains to > > > > synchronize_srcu_atomic(). > > > > > > > > Add srcu_reader_flavor to the Tiny SRCU state for these checks. > > > > Tiny SRCU does not currently set the flavor for atomic SRCU domains, > > > > but keeping the flavor in the common state allows the operation > > > > checks to enforce the restriction once atomic flavor tracking is > > > > enabled. > > > > > > > > Also initialize srcu_atomic_gp_flag, which was previously left > > > > uninitialized. > > > > > > > > Signed-off-by: Kunwu Chan <[email protected]> > > > > --- > > > > include/linux/srcutiny.h | 1 + > > > > kernel/rcu/srcutiny.c | 12 ++++++++++++ > > > > 2 files changed, 13 insertions(+) > > > > > > > > diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h > > > > index 47a368f945e3..2b293336525a 100644 > > > > --- a/include/linux/srcutiny.h > > > > +++ b/include/linux/srcutiny.h > > > > @@ -20,6 +20,7 @@ struct srcu_struct { > > > > u8 srcu_gp_running; /* GP workqueue running? */ > > > > u8 srcu_gp_waiting; /* GP waiting for readers? */ > > > > u8 srcu_atomic_gp_flag; /* Serialize atomic GP work.*/ > > > > + u8 srcu_reader_flavor; /* Values: SRCU_READ_FLAVOR_.* */ > > > > unsigned long srcu_idx; /* Current reader array element > > > > in bit 0x2. */ > > > > unsigned long srcu_idx_max; /* Furthest future srcu_idx > > > > request. */ > > > > struct swait_queue_head srcu_wq; > > > > diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c > > > > index 26ea4bfbeaf2..22f7716cbb0e 100644 > > > > --- a/kernel/rcu/srcutiny.c > > > > +++ b/kernel/rcu/srcutiny.c > > > > @@ -41,6 +41,7 @@ static int init_srcu_struct_fields(struct srcu_struct > > > > *ssp) > > > > ssp->srcu_cb_tail = &ssp->srcu_cb_head; > > > > ssp->srcu_gp_running = false; > > > > ssp->srcu_gp_waiting = false; > > > > + ssp->srcu_atomic_gp_flag = 0; > > > > > > Good catch! I will be folding this into the base commit with attribution > > > on my next rebase: > > > > > > 9a2e9996ccec ("srcutiny: Add an atomic Tiny SRCU") > > > > > > > ssp->srcu_idx = 0; > > > > ssp->srcu_idx_max = 0; > > > > INIT_WORK(&ssp->srcu_work, srcu_drive_gp); > > > > @@ -289,6 +290,9 @@ EXPORT_SYMBOL_GPL(srcu_defer_drain); > > > > void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, > > > > rcu_callback_t func) > > > > { > > > > + if (WARN_ON_ONCE(ssp->srcu_reader_flavor == > > > > SRCU_READ_FLAVOR_ATOMIC)) > > > > + return; > > > > + > > > > if (should_rcu_defer()) { > > > > /* A re-entrant call_srcu() during the drain would > > > > livelock it. */ > > > > if (READ_ONCE(srcu_defer_draining) && !in_nmi()) { > > > > @@ -319,6 +323,11 @@ void synchronize_srcu(struct srcu_struct *ssp) > > > > { > > > > struct rcu_synchronize rs; > > > > > > > > + if (WARN_ON_ONCE(ssp->srcu_reader_flavor == > > > > SRCU_READ_FLAVOR_ATOMIC)) { > > > > + synchronize_srcu_atomic(ssp); > > > > + return; > > > > + } > > > > + > > > > srcu_lock_sync(&ssp->dep_map); > > > > > > > > RCU_LOCKDEP_WARN(lockdep_is_held(ssp) || > > > > @@ -415,6 +424,9 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_atomic); > > > > /* Register any deferred callbacks, then wait for all in-flight ones. > > > > */ > > > > void srcu_barrier(struct srcu_struct *ssp) > > > > { > > > > + if (WARN_ON_ONCE(ssp->srcu_reader_flavor == > > > > SRCU_READ_FLAVOR_ATOMIC)) > > > > + return; > > > > + > > > > __srcu_defer_drain(ssp); > > > > synchronize_srcu(ssp); > > > > } > > > > > > The rest is good as far as it goes, but don't we need to set the value > > > of ssp->srcu_reader_flavor somewhere for atomic srcu_struct structures? > > > > > > > Hi Paul, > > > > Yes, agreed. I have the flavor tracking changes implemented locally > > and am testing them now. > > I’ll send the updated patch shortly. > > > > I also have draft patches for the documentation and the fast path, as > > well as rcutorture testing for > > tiny atomic srcu , which I’ll send separately. > > Sounds good, and I am looking forward to seeing them.
Hi Paul, I’ve sent the flavor tracking changes as [1]. [1] https://lore.kernel.org/all/[email protected]/ > > I will admit that I am curious as to why Tiny Atomic SRCU needs different > rcutorture testing than does Tree Atomic SRCU, but I will ask myself > that question again when I see your patches. ;-) You’re right that the existing SRCU torture configuration can exercise the atomic path with rcutorture.reader_flavor=0x10. I had prepared the Tiny atomic torture test as a separate draft, mainly adding local configurations for convenience while validating the Tiny and Tree atomic paths. There is no Tiny-specific torture model here. I can adjust the final rcutorture configuration and naming based on your preference. Thanks, KunWu > > Thanx, Paul
