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    SubjectRe: [PATCH RFC 00/11] lock monitor: Separate features related to lock
    On 03/20/10 14:56, Hitoshi Mitake wrote:
    > On 03/19/10 06:16, Frederic Weisbecker wrote:
    > >> And I have a question related to this dynamic patching approach for
    > lockdep.
    > >> If dynamic proving turning on/off is provided,
    > >> lockdep will be confused by inconsistency of lock acquiring log.
    > >>
    > >> Will the sequence,
    > >>
    > >> lock_acquire(l) -> turning off -> lock_release(l) -> turning on ->
    > >> lock_acquire(l)
    > >>
    > >> detected as double acquiring?
    > >>
    > >> Should turning on/off lockdep be done in the time
    > >> when every processes have no lock?
    > >
    > >
    > > There is almost always a process with a lock somewhere ;-)
    >
    > Yeah :)
    >
    > >
    > > This is not a big deal, it's very similar to unfinished scenarios
    > > due to the end of the tracing that can happen anytime and you miss
    > > a lock_release or whatever. We can also begin the tracing anytime,
    > > and you may receive orphan lock_release in the very beginning
    > > because you missed the lock_acquire that happened before the tracing.
    > >
    > > Any locking scenario that doesn't fit into the state machine
    > > or is incomplete must be considered as broken and then ignored.
    > >
    > >
    >
    > I see, thanks.
    > I have to fix state machine of perf lock.
    > Now it doesn't consider read, try and orphan events,
    > it is very incompletely..
    >

    Ah, sorry, I've mentioned that these cases might be
    a problem for validation part of lockdep, not for events.

    If the lock and turning on/off sequence like this happened,
    lock_acquire(l) -> turning off -> lock_release(l) -> turning on ->
    lock_acquire(l)
    this will confuse validator of lockdep.
    At least, task_struct.lockdep_depth will be corrupted.

    And I have a trivial question to Ingo.
    In lockdep, held_locks of task_struct are accessed this arithmetical way
    prev = curr->held_locks + i;
    Of course this is valid way, but I feel it is more simple and natural way
    prev = curr->held_locks[i];

    Is there a reason for this style?
    This is a pure question. I have no intention to rewrite them :)

    Thanks,
    Hitoshi


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