On Fri, 2013-03-15 at 03:54 -0700, Michel Lespinasse wrote:
> Remove the rwsem_down_failed_common function and replace it with two
> identical copies of its code in rwsem_down_{read,write}_failed.
>
> This is because we want to make different optimizations in
> rwsem_down_{read,write}_failed; we are adding this pure-duplication
> step as a separate commit in order to make it easier to check the
> following steps.
>
> Signed-off-by: Michel Lespinasse <wal...@google.com>
>
> ---
> lib/rwsem.c | 72
> ++++++++++++++++++++++++++++++++++++++++++++++++-------------
> 1 file changed, 57 insertions(+), 15 deletions(-)
>
> diff --git a/lib/rwsem.c b/lib/rwsem.c
> index 40636454cf3c..fb658af1c12c 100644
> --- a/lib/rwsem.c
> +++ b/lib/rwsem.c
> @@ -178,12 +178,12 @@ try_again_write:
> }
>
> /*
> - * wait for a lock to be granted
> + * wait for the read lock to be granted
> */
> -static struct rw_semaphore __sched *
> -rwsem_down_failed_common(struct rw_semaphore *sem,
> - enum rwsem_waiter_type type, signed long adjustment)
> +struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
> {
> + enum rwsem_waiter_type type = RWSEM_WAITING_FOR_READ;
> + signed long adjustment = -RWSEM_ACTIVE_READ_BIAS;
Again, just my opinion (and I suspect you only did this because that's
what was here) but I think this should be:
+ long adjustment = -RWSEM_ACTIVE_READ_BIAS;
> struct rwsem_waiter waiter;
> struct task_struct *tsk = current;
> signed long count;
Same here.
> @@ -238,21 +238,63 @@ rwsem_down_failed_common(struct rw_semaphore *sem,
> }
>
> /*
> - * wait for the read lock to be granted
> - */
> -struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
> -{
> - return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_READ,
> - -RWSEM_ACTIVE_READ_BIAS);
> -}
> -
> -/*
> * wait for the write lock to be granted
> */
> struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore
> *sem)
> {
> - return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_WRITE,
> - -RWSEM_ACTIVE_WRITE_BIAS);
> + enum rwsem_waiter_type type = RWSEM_WAITING_FOR_WRITE;
> + signed long adjustment = -RWSEM_ACTIVE_WRITE_BIAS;
Same here.
> + struct rwsem_waiter waiter;
> + struct task_struct *tsk = current;
> + signed long count;
And here.
> +
> + /* set up my own style of waitqueue */
> + waiter.task = tsk;
> + waiter.type = type;
> + get_task_struct(tsk);
> +
> + raw_spin_lock_irq(&sem->wait_lock);
> + if (list_empty(&sem->wait_list))
> + adjustment += RWSEM_WAITING_BIAS;
> + list_add_tail(&waiter.list, &sem->wait_list);
> +
> + /* we're now waiting on the lock, but no longer actively locking */
> + count = rwsem_atomic_update(adjustment, sem);
> +
> + /* If there are no active locks, wake the front queued process(es) up.
> + *
> + * Alternatively, if we're called from a failed down_write(), there
> + * were already threads queued before us and there are no active
> + * writers, the lock must be read owned; so we try to wake any read
> + * locks that were queued ahead of us. */
> + if (count == RWSEM_WAITING_BIAS)
> + sem = __rwsem_do_wake(sem, RWSEM_WAKE_NO_ACTIVE);
> + else if (count > RWSEM_WAITING_BIAS &&
> + adjustment == -RWSEM_ACTIVE_WRITE_BIAS)
> + sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED);
> +
> + raw_spin_unlock_irq(&sem->wait_lock);
> +
> + /* wait to be given the lock */
> + while (true) {
> + set_task_state(tsk, TASK_UNINTERRUPTIBLE);
> + if (!waiter.task)
> + break;
> +
> + raw_spin_lock_irq(&sem->wait_lock);
> + /* Try to get the writer sem, may steal from the head writer: */
> + if (type == RWSEM_WAITING_FOR_WRITE)
> + if (try_get_writer_sem(sem, &waiter)) {
> + raw_spin_unlock_irq(&sem->wait_lock);
> + return sem;
> + }
> + raw_spin_unlock_irq(&sem->wait_lock);
> + schedule();
> + }
> +
> + tsk->state = TASK_RUNNING;
> +
> + return sem;
> }
>
> /*
--
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