linux-kernel - Re: [PATCH 3/4] rwsem: implement write lock stealing

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Date:	Sat, 9 Feb 2013 15:30:06 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	linux-kernel@...r.kernel.org, anton@...ba.org, hpa@...or.com,
	mingo@...nel.org, arjan@...ux.intel.com, a.p.zijlstra@...llo.nl,
	torvalds@...ux-foundation.org, alex.shi@...el.com,
	yuanhan.liu@...ux.intel.com, dhowells@...hat.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 3/4] rwsem: implement write lock stealing

On Sat, Feb 9, 2013 at 10:45 AM, Michel Lespinasse <walken@...gle.com> wrote:
> +               if (waiter->type != RWSEM_WAITING_FOR_WRITE) {
> +                       list_del(&waiter->list);
> +
> +                       /* Set RWSEM_WAITING_BIAS before waking the last reader
> +                        * so we know there will be a remaining active locker.
> +                        */
> +                       if (!(--readers) && !list_empty(&sem->wait_list))
> +                               rwsem_atomic_add(RWSEM_WAITING_BIAS, sem);
> +
> +                       tsk = waiter->task;
> +                       smp_mb();

For what with mb?

> +                       waiter->task = NULL;
> +                       wake_up_process(tsk);
> +                       put_task_struct(tsk);
> +               }
> +       } while (readers);
> +       sem->wait_readers = 0;


> +       /* If there are no active locks, wake the front queued process(es). */

s/locks/lockers/

> +       if (!(count & RWSEM_ACTIVE_MASK))
> +               sem = __rwsem_do_wake(sem, RWSEM_WAKE_ANY);
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