Re: [tip:sched/core] sched: Fix ancient race in do_exit()

[Linus Torvalds]

On Sat, Jan 28, 2012 at 4:03 AM, tip-bot for Yasunori Goto
<y-goto@xxxxxxxxxxxxxx> wrote:
>
> sched: Fix ancient race in do_exit()

Ugh.

It would be much nicer to just clear the rwsem waiter->task thing
*after* waking the task up, which would avoid this race entirely,
afaik.

Tell me, why wouldn't that work? rwsem_down_failed_common() does

        /* wait to be given the lock */
        for (;;) {
                if (!waiter.task)
                        break;
               ...

so then we wouldn't need the task refcount crap in rwsem either etc,
and we'd get rid of all races with wakeup.

I wonder why we're clearing that whole waiter->task so early.

                       Linus
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