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    SubjectRe: [PATCH] Increase lockdep MAX_LOCK_DEPTH
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    On Sat, 2007-09-01 at 01:05 +1000, David Chinner wrote:

    > > Trouble is, we'd like to have a sane upper bound on the amount of held
    > > locks at any one time, obviously this is just wanting, because a lot of
    > > lock chains also depend on the number of online cpus...
    >
    > Sure - this is an obvious case where it is valid to take >30 locks at
    > once in a single thread. In fact, worst case here we are taking twice this
    > number of locks - we actually take 2 per inode (ilock and flock) so a
    > full 32 inode cluster free would take >60 locks in the middle of this
    > function and we should be busting this depth couter limit all the
    > time.

    I think this started because jeffpc couldn't boot without XFS busting
    lockdep :-)

    > Do semaphores (the flush locks) contribute to the lock depth
    > counters?

    No, alas, we cannot handle semaphores in lockdep. Semaphores don't have
    a strict owner, hence we cannot track them. This is one of the reasons
    to rid ourselves of semaphores - that and there are very few cases where
    the actual semantics of semaphores are needed. Most of the times code
    using semaphores can be expressed with either a mutex or a completion.

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