On 03/20/10 17:23, Hitoshi Mitake wrote:
> 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];
>
Ah, sorry,
prev = curr->held_locks[i];
is wrong. It's
prev = &curr->held_locks[i];
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