[PATCH bug-fix] drbd: compute the end before rb_insert_augmented()

[Lai Jiangshan <laijs@cn.fujitsu.com>]

986836503e49 ("Merge branch 'drbd-8.4_ed6' into for-3.8-drivers-drbd-8.4_ed6")
changes rb_augment_insert() to new augment API.  But the new API
rb_insert_augmented() requires the tree is augmennted before called.

Quote from Documentation/rbtree.txt:
"""
  On insertion, the user must update the augmented information on the path
  leading to the inserted node, then call rb_link_node() as usual and
  rb_augment_inserted() instead of the usual rb_insert_color() call.
  If rb_augment_inserted() rebalances the rbtree, it will callback into
  a user provided function to update the augmented information on the
  affected subtrees.
"""

So we add the augment-code to drbd_insert_interval() when it travels
the tree up to down before rb_insert_augmented().  See the example in
include/linux/interval_tree_generic.h or Documentation/rbtree.txt.

drbd_insert_interval() may cancel the insertion when traveling,
in this case, the just added augment-code does nothing before cancel
since the @this node is already in the subtrees in this case.

CC: Michel Lespinasse <walken@google.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
 drivers/block/drbd/drbd_interval.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/drivers/block/drbd/drbd_interval.c b/drivers/block/drbd/drbd_interval.c
index 89c497c..04a14e0 100644
--- a/drivers/block/drbd/drbd_interval.c
+++ b/drivers/block/drbd/drbd_interval.c
@@ -79,6 +79,7 @@ bool
 drbd_insert_interval(struct rb_root *root, struct drbd_interval *this)
 {
 	struct rb_node **new = &root->rb_node, *parent = NULL;
+	sector_t this_end = this->sector + (this->size >> 9);
 
 	BUG_ON(!IS_ALIGNED(this->size, 512));
 
@@ -87,6 +88,8 @@ drbd_insert_interval(struct rb_root *root, struct drbd_interval *this)
 			rb_entry(*new, struct drbd_interval, rb);
 
 		parent = *new;
+		if (here->end < this_end)
+			here->end = this_end;
 		if (this->sector < here->sector)
 			new = &(*new)->rb_left;
 		else if (this->sector > here->sector)
@@ -99,6 +102,7 @@ drbd_insert_interval(struct rb_root *root, struct drbd_interval *this)
 			return false;
 	}
 
+	this->end = this_end;
 	rb_link_node(&this->rb, parent, new);
 	rb_insert_augmented(&this->rb, root, &augment_callbacks);
 	return true;
-- 
1.7.4.4