On 03/02, Oleg Nesterov wrote:
>
> On 03/02, Lai Jiangshan wrote:
> >
> > +void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw)
> > +{
> > + switch (__this_cpu_read(*lgrw->reader_refcnt)) {
> > + case 1:
> > + __this_cpu_write(*lgrw->reader_refcnt, 0);
> > + lg_local_unlock(&lgrw->lglock);
> > + return;
> > + case FALLBACK_BASE:
> > + __this_cpu_write(*lgrw->reader_refcnt, 0);
> > + read_unlock(&lgrw->fallback_rwlock);
> > + rwlock_release(&lg->lock_dep_map, 1, _RET_IP_);
>
> I guess "case 1:" should do rwlock_release() too.
>
> Otherwise, at first glance looks correct...
>
> However, I still think that FALLBACK_BASE only adds the unnecessary
> complications. But even if I am right this is subjective of course, please
> feel free to ignore.
Yes, but...
> And btw, I am not sure about lg->lock_dep_map, perhaps we should use
> fallback_rwlock->dep_map ?
>
> We need rwlock_acquire_read() even in the fast-path, and this acquire_read
> should be paired with rwlock_acquire() in _write_lock(), but it does
> spin_acquire(lg->lock_dep_map). Yes, currently this is the same (afaics)
> but perhaps fallback_rwlock->dep_map would be more clean.
Please ignore this part.
I missed that lg_rwlock_global_write_lock() relies on lg_global_lock(),
and I just noticed that it does rwlock_acquire(lg->lock_dep_map).
Hmm. But then I do not understand the lglock annotations. Obviously,
rwlock_acquire_read() in lg_local_lock() can't even detect the simplest
deadlock, say, lg_local_lock(LOCK) + lg_local_lock(LOCK). Not to mention
spin_lock(X) + lg_local_lock(Y) vs lg_local_lock(Y) + spin_lock(X).
OK, I understand that it is not easy to make these annotations correct...
Oleg.
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