On Sat, Apr 13, 2019 at 01:22:54PM -0400, Waiman Long wrote: > @@ -650,6 +686,33 @@ __rwsem_down_read_failed_common(struct rw_semaphore > *sem, int state) > struct rwsem_waiter waiter; > DEFINE_WAKE_Q(wake_q); > > + if (!rwsem_can_spin_on_owner(sem)) > + goto queue; > + > + /* > + * Undo read bias from down_read() and do optimistic spinning. > + */ > + atomic_long_add(-RWSEM_READER_BIAS, &sem->count); > + adjustment = 0; > + if (rwsem_optimistic_spin(sem, false)) { > + unsigned long flags; > + > + /* > + * Opportunistically wake up other readers in the wait queue. > + * It has another chance of wakeup at unlock time. > + */ > + if ((atomic_long_read(&sem->count) & RWSEM_FLAG_WAITERS) && > + raw_spin_trylock_irqsave(&sem->wait_lock, flags)) {
why trylock? Also the rest of this function uses _irq(). Having had to define @flags should've been a clue. You simply cnanot do down_*() with IRQs disabled. > + if (!list_empty(&sem->wait_list)) > + __rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, > + &wake_q); > + raw_spin_unlock_irqrestore(&sem->wait_lock, flags); > + wake_up_q(&wake_q); > + } > + return sem; > + } > + > +queue: > waiter.task = current; > waiter.type = RWSEM_WAITING_FOR_READ; > waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;