Re: [PATCH RFC 00/11] lock monitor: Separate features related tolock

[Hitoshi Mitake]

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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