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    SubjectRe: Async resume patch (was: Re: [GIT PULL] PM updates for 2.6.33)
    On Tuesday 08 December 2009, Linus Torvalds wrote:
    > On Tue, 8 Dec 2009, Rafael J. Wysocki wrote:
    > >
    > > The wait queue plus the op_complete flag combo plays the role of the locking
    > > in the Linus' picture
    > Please just use the lock. Don't make up your own locking crap. Really.
    > Your patch is horrible. Exactly because your locking is horribly
    > mis-designed. You can't say things are complete from an interrupt, for
    > example, since you made it some random bitfield, which has unknown
    > characteristics (ie non-atomic read-modify-write etc).

    I didn't assume anyone would check it from an interrupt, because I didn't see
    a point. In fact I didn't assume anyone except for the PM core would check it.
    In case this assumption is wrong, it can be easily put under the dev->sem
    that we take anyway before calling the bus type (etc.) callbacks.

    Anyway, if we use an rwsem, it won't be checkable from interrupt context just
    as well.

    > The fact is, any time anybody makes up a new locking mechanism, THEY
    > ALWAYS GET IT WRONG. Don't do it.
    > I suggested using the rwsem locking for a good reason. It made sense. It
    > was simpler. Just do it that way, stop making up crap.

    Suppose we use rwsem and during suspend each child uses a down_read() on a
    parent and then the parent uses down_write() on itself. What if, whatever the
    reason, the parent is a bit early and does the down_write() before one of the
    children has a chance to do the down_read()? Aren't we toast?

    Do we need any direct protection against that or does it just work itself out
    in a way I just don't see right now?


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      Last update: 2009-12-08 20:47    [W:0.023 / U:75.460 seconds]
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