Re: [PATCH] RT: Checks for cmpxchg in get_task_struct_rcu()

[Nick Piggin <nickpiggin@yahoo.com.au>]

Daniel Walker wrote:

> +#else
> +	raw_local_irq_disable();
> +	oldusage = atomic_read(&t->usage);
> +	if (oldusage == 0) {
> +		raw_local_irq_enable();
> +		return 0;
> +	}

Isn't this still racy if another cpu drops the last reference
to task struct here? Or can't that happen?

When you said "disable preempt", I had some silly idea that this
function was only used in PREEMPT_RT mode, and that you would
simply disallow architectures without cmpxchg from configuring
PREEMPT_RT.

> +	atomic_inc(&t->usage);
> +	raw_local_irq_enable();
> +#endif

--
SUSE Labs, Novell Inc.

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