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

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