On 03/03/13 01:20, Oleg Nesterov wrote:

On 03/02, Lai Jiangshan wrote:

quoted

+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.

Already do it in "lg_local_unlock(&lgrw->lglock);" before it returns.
(I like reuse old code)

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.

OK, I kill FALLBACK_BASE in later patch.

And btw, I am not sure about lg->lock_dep_map, perhaps we should use
fallback_rwlock->dep_map ?

Use either one is OK.

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.

I can't tell which one is better. I try to use fallback_rwlock->dep_map later.

Oleg.

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