Re: [PATCH 2/6] locking: Introduce range reader/writer lock

[Davidlohr Bueso]

On Tue, 18 Apr 2017, Laurent Dufour wrote:

On 06/04/2017 10:46, Davidlohr Bueso wrote:

+__range_read_lock_common(struct range_rwlock_tree *tree,
+                        struct range_rwlock *lock, long state)
+{
+       struct interval_tree_node *node;
+       unsigned long flags;
+
+       spin_lock_irqsave(&tree->lock, flags);
+       range_lock_set_reader(lock);
+
+       if (!__range_intersects_intree(tree, lock))
+               goto insert;
+
+       range_interval_tree_foreach(node, &tree->root,
+                                   lock->node.start, lock->node.last) {
+               struct range_rwlock *blocked_lock;
+               blocked_lock = range_entry(node, struct range_rwlock, node);
+
+               if (!range_lock_is_reader(blocked_lock))
+                       lock->blocking_ranges++;
+       }
+insert:
+       __range_tree_insert(tree, lock);
+
+       lock->waiter = current;

Hi Davidlohr,

Setting lock->waiter after calling range_lock_set_reader() is resetting
the reader flag. Moving the call to range_lock_set_reader() here fixes that.

Yeah, I moved the set_reader() call to after setting lock->waiter.

+       spin_unlock_irqrestore(&tree->lock, flags);
+
+       return wait_for_ranges(tree, lock, state);
+}

[...]

+int range_read_trylock(struct range_rwlock_tree *tree, struct range_rwlock 
*lock)
+{
+       int ret = true;
+       unsigned long flags;
+       struct interval_tree_node *node;
+
+       spin_lock_irqsave(&tree->lock, flags);
+
+       if (!__range_intersects_intree(tree, lock))
+               goto insert;
+
+       /*
+        * We have overlapping ranges in the tree, ensure that we can
+        * in fact share the lock.
+        */
+       range_interval_tree_foreach(node, &tree->root,
+                                   lock->node.start, lock->node.last) {
+               struct range_rwlock *blocked_lock;
+               blocked_lock = range_entry(node, struct range_rwlock, node);
+
+               if (!range_lock_is_reader(blocked_lock)) {
+                       ret = false;
+                       goto unlock;
+               }
+       }
+insert:
+       range_lock_set_reader(lock);

Here, the lock->waiter field should have been set to current before
calling range_lock_set_reader()

But this is a trylock attempt, there is no waiting going on.

Thanks,
Davidlohr