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SubjectRe: [RFC/PATCH] debug workqueue deadlocks with lockdep

* Johannes Berg <johannes@sipsolutions.net> wrote:

> > > @@ -257,7 +260,9 @@ static void run_workqueue(struct cpu_wor
> > >
> > > BUG_ON(get_wq_data(work) != cwq);
> > > work_clear_pending(work);
> > > + lock_acquire(&cwq->wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
> > > f(work);
> > > + lock_release(&cwq->wq->lockdep_map, 0, _THIS_IP_);
> > ^^^
> > Isn't it better to call lock_release() with nested == 1 ?
>
> Not sure, Ingo?

well, in this case the lock/unlock should nest perfectly (i.e. it should
always be balanced perfectly), so indeed calling with nested==1 leads to
stricter checking.

non-nested unlocks occur when people do stuff like:

spin_lock(&lock1);
spin_lock(&lock2);
spin_unlock(&lock1);
spin_unlock(&lock2);

the first unlock is not 'nested perfectly'. Now for the workqueue
dep_map this shouldnt be a legal combination, right?

Ingo
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