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Date: Wed, 05 May 2004 21:17:01 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
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To: William Lee Irwin III <wli@holomorphy.com>
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Subject: Re: 2.6.6-rc3-mm2
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Hello.

William Lee Irwin III wrote:
> 
> On Wed, May 05, 2004 at 04:17:05PM +0400, Oleg Nesterov wrote:
> > also, exclusive wakeups have no problems, and process
> > waiting in wait_on_page_writeback() won't be waken
> > by unlock_page(). it will be waken _only_ when that
> > bit will be cleared.
> 
> The object isn't passed down to the wake function at all, so it can't
> avoid falsely scheduling waiters on the wrong objects and/or bits.

I think you are wrong. __wake_up_common() calls wait_queue_t().func,
which is wake_bit_function(). It casts wait argument to wait_bit_queue,
and checks test_bit(wait_bit->bit_nr, wait_bit->flags) in _waker_
context, and wakes up wait->task _only_ if that bit is cleared,
so there is no false wakeups.

Oleg.