On Wed, 8 Jan 2025 at 07:49, Waiman Long <llong@xxxxxxxxxx> wrote: > > On 1/7/25 8:59 AM, Kumar Kartikeya Dwivedi wrote: > > The pending bit is used to avoid queueing in case the lock is > > uncontended, and has demonstrated benefits for the 2 contender scenario, > > esp. on x86. In case the pending bit is acquired and we wait for the > > locked bit to disappear, we may get stuck due to the lock owner not > > making progress. Hence, this waiting loop must be protected with a > > timeout check. > > > > To perform a graceful recovery once we decide to abort our lock > > acquisition attempt in this case, we must unset the pending bit since we > > own it. All waiters undoing their changes and exiting gracefully allows > > the lock word to be restored to the unlocked state once all participants > > (owner, waiters) have been recovered, and the lock remains usable. > > Hence, set the pending bit back to zero before returning to the caller. > > > > Introduce a lockevent (rqspinlock_lock_timeout) to capture timeout > > event statistics. > > > > Reviewed-by: Barret Rhoden <brho@xxxxxxxxxx> > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> > > --- > > include/asm-generic/rqspinlock.h | 2 +- > > kernel/locking/lock_events_list.h | 5 +++++ > > kernel/locking/rqspinlock.c | 28 +++++++++++++++++++++++----- > > 3 files changed, 29 insertions(+), 6 deletions(-) > > > > diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h > > index 8ed266f4e70b..5c996a82e75f 100644 > > --- a/include/asm-generic/rqspinlock.h > > +++ b/include/asm-generic/rqspinlock.h > > @@ -19,6 +19,6 @@ struct qspinlock; > > */ > > #define RES_DEF_TIMEOUT (NSEC_PER_SEC / 2) > > > > -extern void resilient_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val, u64 timeout); > > +extern int resilient_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val, u64 timeout); > > > > #endif /* __ASM_GENERIC_RQSPINLOCK_H */ > > diff --git a/kernel/locking/lock_events_list.h b/kernel/locking/lock_events_list.h > > index 97fb6f3f840a..c5286249994d 100644 > > --- a/kernel/locking/lock_events_list.h > > +++ b/kernel/locking/lock_events_list.h > > @@ -49,6 +49,11 @@ LOCK_EVENT(lock_use_node4) /* # of locking ops that use 4th percpu node */ > > LOCK_EVENT(lock_no_node) /* # of locking ops w/o using percpu node */ > > #endif /* CONFIG_QUEUED_SPINLOCKS */ > > > > +/* > > + * Locking events for Resilient Queued Spin Lock > > + */ > > +LOCK_EVENT(rqspinlock_lock_timeout) /* # of locking ops that timeout */ > > + > > /* > > * Locking events for rwsem > > */ > > Since the build of rqspinlock.c is conditional on > CONFIG_QUEUED_SPINLOCKS, this lock event should be inside the > CONFIG_QUEUED_SPINLOCKS block. Ack, I will fix this. > > Cheers, > Longman > >
