[PATCH] hfsplus: fix hfs_bnode_split() failure on sparsely-filled nodes

[Shardul Bankar <shardul.b@mpiricsoftware.com>]

hfs_bnode_split() determines the split point by scanning the node's
offset table for the first record whose data offset exceeds a threshold
derived from node_size / 2. When all record data fits within the first
half of the node, no record offset exceeds the threshold, the loop
exhausts all records, and the function returns -ENOSPC even though the
node can be validly split. This causes xattr insertions to fail
silently.

The failing code path is exercised by xfstests generic/070 and
generic/642 during xattr stress operations.

Fix this by re-scanning with a threshold based on the actual data
midpoint when the position-based scan exhausts. If the re-scan also
exhausts, fall back to splitting off the last record.

Reported-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Shardul Bankar <shardul.b@mpiricsoftware.com>
---
 fs/hfsplus/brec.c | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/fs/hfsplus/brec.c b/fs/hfsplus/brec.c
index e3df89284079..cfc909c808a4 100644
--- a/fs/hfsplus/brec.c
+++ b/fs/hfsplus/brec.c
@@ -282,12 +282,32 @@ static struct hfs_bnode *hfs_bnode_split(struct hfs_find_data *fd)
 		old_rec_off -= rec_size;
 		if (++num_recs < node->num_recs)
 			continue;
-		hfs_bnode_put(node);
-		hfs_bnode_unlink(new_node);
-		hfs_bnode_put(new_node);
-		if (next_node)
-			hfs_bnode_put(next_node);
-		return ERR_PTR(-ENOSPC);
+		/*
+		 * All data fits within the node_size/2 threshold,
+		 * so re-scan using the actual data midpoint.
+		 */
+		size = hfs_bnode_read_u16(node, tree->node_size -
+			(node->num_recs + 1) * rec_size);
+		size = ((int)node_desc_size + size) / 2;
+		old_rec_off = tree->node_size - (2 * rec_size);
+		num_recs = 1;
+		for (;;) {
+			data_start = hfs_bnode_read_u16(node,
+							old_rec_off);
+			if (data_start > size)
+				break;
+			old_rec_off -= rec_size;
+			if (++num_recs < node->num_recs)
+				continue;
+			/* last record holds most of the data */
+			num_recs = node->num_recs - 1;
+			old_rec_off = tree->node_size -
+				(num_recs + 1) * rec_size;
+			data_start = hfs_bnode_read_u16(node,
+							old_rec_off);
+			break;
+		}
+		break;
 	}
 
 	if (fd->record + 1 < num_recs) {
-- 
2.34.1