Messages in this thread | | | Date | Wed, 12 Nov 2008 12:58:04 +0100 | From | Oleg Nesterov <> | Subject | Re: [RFC,PATCH] workqueues: turn queue_work() into the "barrier" for work->func() |
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On 11/11, David Howells wrote: > > Oleg Nesterov <oleg@redhat.com> wrote: > > > I think the caller of queue_work() has all rights to expect that > > the next invocation of work_func() must see "VAR == 1", but this > > is not true if the work is already pending. > > As you said, queue_work() does test_and_set_bit() which implies smp_mb() > either side of the function, so you're half way there, and run_workqueue() > calls spin_unlock_irq() just before calling work_clear_pending()... So might > it make sense to move the work_clear_pending() into locked section? Or would > that require an smp_mb__before_clear_bit()?
This can't really help, afaics. We still need mb() between clear_bit(_PENDING) and LOAD(VAR). Because unlock() is the "one way" barrier, LOAD(VAR) can leak into the critical section, and it can be re-ordered with clear_bit() inside the critical section.
Oleg.
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