Messages in this thread | | | Date | Fri, 23 Jan 2009 13:36:33 +0100 | Subject | Re: [RFC v4] wait: prevent waiter starvation in __wait_on_bit_lock | From | Dmitry Adamushko <> |
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2009/1/23 Oleg Nesterov <oleg@redhat.com>: > On 01/23, Dmitry Adamushko wrote: >> >> 2009/1/23 Oleg Nesterov <oleg@redhat.com>: >> > On 01/23, Dmitry Adamushko wrote: >> >> >> >> In short, wq->lock is a sync. mechanism in this case. The scheme is as follows: >> >> >> >> our side: >> >> >> >> [ finish_wait() ] >> >> >> >> lock(wq->lock); >> > >> > But we can skip lock(wq->lock), afaics. >> > >> > Without rmb(), test_bit() can be re-ordered with list_empty_careful() >> > in finish_wait() and even with __set_task_state(TASK_RUNNING). >> >> But taking into account the constraints of this special case, namely >> (1), we can't skip lock(wq->lock). >> >> (1) "the next contender is us" >> >> In this particular situation, we are only interested in the case when >> we were woken up by __wake_up_bit(). > > Yes, > >> that means we are _on_ the 'wq' list when we do finish_wait() -> we do >> take the 'wq->lock'. > > Hmm. No? > > We are doing exclusive wait, and we use autoremove_wake_function(). > If we were woken, we are removed from ->task_list.
Argh, right, somehow I've made wrong assumptions on the wake-up part :-/
> > Oleg. >
-- Best regards, Dmitry Adamushko
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