erofs: fix refcount on the metabuf used for inode lookup

In erofs_find_target_block() when erofs_dirnamecmp() returns 0, we do not assign the target metabuf. This causes the caller erofs_namei()'s erofs_put_metabuf() at the end to be not effective leaving the refcount on the page.
As the page from metabuf (buf->page) is never put, such page cannot be migrated or reclaimed. Fix it now by putting the metabuf from previous loop and assigning the current metabuf to target before returning so caller erofs_namei() can do the final put as it was intended.

Fixes 500edd095648 ("erofs: use meta buffers for inode lookup")

Cc [email protected]

Signed-off-by Sandeep Dhavale <[email protected]>

In erofs_find_target_block() when erofs_dirnamecmp() returns 0, we do not assign the target metabuf. This causes the caller erofs_namei()'s erofs_put_metabuf() at the end to be not effective leaving the refcount on the page.
As the page from metabuf (buf->page) is never put, such page cannot be migrated or reclaimed. Fix it now by putting the metabuf from previous loop and assigning the current metabuf to target before returning so caller erofs_namei() can do the final put as it was intended.

Fixes 500edd095648 ("erofs: use meta buffers for inode lookup")

Cc [email protected]

Signed-off-by Sandeep Dhavale <[email protected]>

---
Changes since v1
- Rearrange the cases as suggested by Gao so there is less duplication of the code and it is more readable

 fs/erofs/namei.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

fs/erofs/namei.c +14 -14

index d4f631d39f0f..f0110a78acb2 100644
@@ -130,24 +130,24 @@ static void *erofs_find_target_block(struct erofs_buf *target,
 			/* string comparison without already matched prefix */
 			diff = erofs_dirnamecmp(name, &dname, &matched);
 
-			if (!diff) {
-				*_ndirents = 0;
-				goto out;
-			} else if (diff > 0) {
-				head = mid + 1;
-				startprfx = matched;
-
-				if (!IS_ERR(candidate))
-					erofs_put_metabuf(target);
-				*target = buf;
-				candidate = de;
-				*_ndirents = ndirents;
-			} else {
+			if (diff < 0) {
 				erofs_put_metabuf(&buf);
-
 				back = mid - 1;
 				endprfx = matched;
+				continue;
+			}
+
+			if (!IS_ERR(candidate))
+				erofs_put_metabuf(target);
+			*target = buf;
+			if (!diff) {
+				*_ndirents = 0;
+				return de;
 			}
+			head = mid + 1;
+			startprfx = matched;
+			candidate = de;
+			*_ndirents = ndirents;
 			continue;
 		}
 out:		/* free if the candidate is valid */

In erofs_find_target_block() when erofs_dirnamecmp() returns 0, we do not assign the target metabuf. This causes the caller erofs_namei()'s erofs_put_metabuf() at the end to be not effective leaving the refcount on the page.
As the page from metabuf (buf->page) is never put, such page cannot be migrated or reclaimed. Fix it now by putting the metabuf from previous loop and assigning the current metabuf to target before returning so caller erofs_namei() can do the final put as it was intended.

Fixes 500edd095648 ("erofs: use meta buffers for inode lookup")

Cc [email protected]

Signed-off-by Sandeep Dhavale <[email protected]>