Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation

[Nick Piggin]

David Howells wrote:

> +	/* set up my own style of waitqueue */
> +	waiter.task = tsk;
> +

Any reason why you're setting up your own style of waitqueue in
mutex-simple.c instead of just using the kernel's style of waitqueue?

> +
> +/*
> + * release a single token back to a mutex
> + * - entered with lock held and interrupts disabled
> + * - the queue will not be empty
> + */
> +void __up(struct mutex *mutex)
> +{
> +	struct mutex_waiter *waiter;
> +	struct task_struct *tsk;
> +
> +	/* grant the token to the process at the front of the queue */
> +	waiter = list_entry(mutex->wait_list.next, struct mutex_waiter, list);
> +
> +	/* we must be careful not to touch 'waiter' after we set ->task = NULL.
> +	 * - it is an allocated on the waiter's stack and may become invalid at
> +	 *   any time after that point (due to a wakeup from another source).
> +	 */
> +	list_del_init(&waiter->list);
> +	tsk = waiter->task;
> +#ifdef CONFIG_DEBUG_MUTEX_OWNER
> +	mutex->__owner = tsk;
> +#endif
> +	mb();

This should be smp_mb(), I think.

> +	waiter->task = NULL;
> +	wake_up_process(tsk);
> +	put_task_struct(tsk);
> +}

Thanks,
Nick

--
SUSE Labs, Novell Inc.

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