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Also use READ_ONCE() outside > wait_lock critical sections for read and WRITE_ONCE() inside wait_lock > critical sections for write for proper synchronization. There is no > functional change. Hi, Do we need Fixes: d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling more consistent") Fixes: 91d2a812dfb9 ("locking/rwsem: Make handoff writer optimistically spin on owner") Cc: stable@vger.kernel.org clauses added to patches 3,4,5 so they are all picked up in one series ? Thank you, John. > > Signed-off-by: Waiman Long > --- > kernel/locking/rwsem.c | 21 +++++++++++++-------- > 1 file changed, 13 insertions(+), 8 deletions(-) > > diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c > index c68d76fc8c68..a8bfc905637a 100644 > --- a/kernel/locking/rwsem.c > +++ b/kernel/locking/rwsem.c > @@ -338,12 +338,17 @@ enum rwsem_waiter_type { > RWSEM_WAITING_FOR_READ > }; > > +enum rwsem_handoff_state { > + HANDOFF_NONE = 0, > + HANDOFF_REQUESTED, > +}; > + > struct rwsem_waiter { > struct list_head list; > struct task_struct *task; > enum rwsem_waiter_type type; > + enum rwsem_handoff_state handoff_state; > unsigned long timeout; > - bool handoff_set; > }; > #define rwsem_first_waiter(sem) \ > list_first_entry(&sem->wait_list, struct rwsem_waiter, list) > @@ -470,7 +475,7 @@ static void rwsem_mark_wake(struct rw_semaphore *sem, > adjustment -= RWSEM_FLAG_HANDOFF; > lockevent_inc(rwsem_rlock_handoff); > } > - waiter->handoff_set = true; > + WRITE_ONCE(waiter->handoff_state, HANDOFF_REQUESTED); > } > > atomic_long_add(-adjustment, &sem->count); > @@ -622,7 +627,7 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem, > * waiter is the one that set it. Otherwisee, we > * still try to acquire the rwsem. > */ > - if (first->handoff_set && (waiter != first)) > + if (first->handoff_state && (waiter != first)) > return false; > } > > @@ -650,11 +655,11 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem, > > /* > * We have either acquired the lock with handoff bit cleared or set > - * the handoff bit. Only the first waiter can have its handoff_set > + * the handoff bit. Only the first waiter can have its handoff_state > * set here to enable optimistic spinning in slowpath loop. > */ > if (new & RWSEM_FLAG_HANDOFF) { > - first->handoff_set = true; > + WRITE_ONCE(first->handoff_state, HANDOFF_REQUESTED); > lockevent_inc(rwsem_wlock_handoff); > return false; > } > @@ -1043,7 +1048,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat > waiter.task = current; > waiter.type = RWSEM_WAITING_FOR_READ; > waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT; > - waiter.handoff_set = false; > + waiter.handoff_state = HANDOFF_NONE; > > raw_spin_lock_irq(&sem->wait_lock); > if (list_empty(&sem->wait_list)) { > @@ -1131,7 +1136,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) > waiter.task = current; > waiter.type = RWSEM_WAITING_FOR_WRITE; > waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT; > - waiter.handoff_set = false; > + waiter.handoff_state = HANDOFF_NONE; > > raw_spin_lock_irq(&sem->wait_lock); > rwsem_add_waiter(sem, &waiter); > @@ -1176,7 +1181,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) > * In this case, we attempt to acquire the lock again > * without sleeping. > */ > - if (waiter.handoff_set) { > + if (READ_ONCE(waiter.handoff_state)) { > enum owner_state owner_state; > > preempt_disable();