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    SubjectRe: [PATCH] rtmutex: multiple candidate owners without unrelated boosting
    On Wed, 2010-12-15 at 09:02 +0100, Thomas Gleixner wrote:
    > On Tue, 14 Dec 2010, Steven Rostedt wrote:
    > > On Tue, 2010-12-14 at 17:04 +0800, Lai Jiangshan wrote:
    > >
    > > OK, I was looking at this in a bit more detail (the coffee finally set
    > > in) and I was at first looking to nuke the cand_owner since it is
    > > redundant to cand_seq. But I think we can nuke the cand_seq instead and
    > > use the top_waiter as the decider.
    > So you just use cand_owner (the name sucks) to flag that the waiter
    > has been woken up either by the boost code or by an unlock. The waiter
    > clears that flag with waiter->lock->wait_lock held before calling
    > schedule().
    > Though I think we do need it at all. wakeup of an already running task
    > is almost a nop, so having one less state to worry about is good.

    I was hoping to remove it completely, and yes I was hoping we could
    because a wakeup of a woken task is almost a nop. But then I saw this in

    > /*
    > * Check the orig_waiter state. After we dropped the locks,
    > * the previous owner of the lock might have released the lock
    > - * and made us the pending owner:
    > + * and made us candidate owner:
    > */
    > - if (orig_waiter && !orig_waiter->task)
    > + if (orig_waiter && orig_waiter->cand_owner)
    > goto out_unlock_pi;

    I'm not sure what else we could use to check if the original waiter has
    been given the lock.

    -- Steve

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