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    SubjectRe: check && lockdep_no_validate (Was: lockdep: Introduce wait-type checks)
    On Thu, Jan 16, 2014 at 06:43:48PM +0100, Oleg Nesterov wrote:
    > But with or without this change the following code
    >
    > static DEFINE_MUTEX(m1);
    > static DEFINE_MUTEX(mx);
    >
    > lockdep_set_novalidate_class(&mx);
    >
    > // m1 -> mx
    > mutex_lock(&m1);
    > mutex_lock(&mx);
    > mutex_unlock(&mx);
    > mutex_unlock(&m1);
    >
    > // mx -> m1 ; should trigger the warning ???
    > mutex_lock(&mx);
    > mutex_lock(&m1);
    > mutex_unlock(&m1);
    > mutex_unlock(&mx);
    >
    > doesn't trigger the warning too. This is correct because
    > lockdep_set_novalidate_class() means, well, no-validate.
    > The question is: do we really want to avoid all validations?

    Good question.

    > Why lockdep_set_novalidate_class() was added? Unlees I missed
    > something the problem is that (say) __driver_attach() can take
    > the "same" lock twice, drivers/base/ lacks annotations.

    Indeed, the driver model locking always slips my mind but yes its
    creative. Alan Stern seems to have a good grasp on it though.

    > Perhaps we should change the meaning of lockdep_set_novalidate_class?
    > (perhaps with rename). What do you think about the patch below?
    >
    > With this patch __lockdep_no_validate__ means "automatically nested",

    Yes, I suppose that might work, it would allow some validation.

    > although I have to remind I can hardly understand the code I am
    > trying to change ;)

    You don't seem to be doing too badly ;-)


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