Re: [patch] queued spinlocks (i386)

[Oleg Nesterov <oleg@tv-sign.ru>]

On 03/28, Nick Piggin wrote:
>
> Well with my queued spinlocks, all that lockbreak stuff can just come out
> of the spin_lock, break_lock out of the spinlock structure, and
> need_lockbreak just becomes (lock->qhead - lock->qtail > 1).

Q: queued spinlocks are not CONFIG_PREEMPT friendly,

> +       asm volatile(LOCK_PREFIX "xaddw %0, %1\n\t"
> +                    : "+r" (pos), "+m" (lock->qhead) : : "memory");
> +       while (unlikely(pos != lock->qtail))
> +               cpu_relax();

once we incremented lock->qhead, we have no optiion but should spin with
preemption disabled until pos == lock->qtail, yes?

Oleg.