xfs: don't leak btree cursor when insrec fails after a split

The recent patch to improve btree cycle checking caused a regression
when I rebased the in-memory btree branch atop the 5.19 for-next branch,
because in-memory short-pointer btrees do not have AG numbers.  This
produced the following complaint from kmemleak:

unreferenced object 0xffff88803d47dde8 (size 264):
  comm "xfs_io", pid 4889, jiffies 4294906764 (age 24.072s)
  hex dump (first 32 bytes):
    90 4d 0b 0f 80 88 ff ff 00 a0 bd 05 80 88 ff ff  .M..............
    e0 44 3a a0 ff ff ff ff 00 df 08 06 80 88 ff ff  .D:.............
  backtrace:
    [<ffffffffa0388059>] xfbtree_dup_cursor+0x49/0xc0 [xfs]
    [<ffffffffa029887b>] xfs_btree_dup_cursor+0x3b/0x200 [xfs]
    [<ffffffffa029af5d>] __xfs_btree_split+0x6ad/0x820 [xfs]
    [<ffffffffa029b130>] xfs_btree_split+0x60/0x110 [xfs]
    [<ffffffffa029f6da>] xfs_btree_make_block_unfull+0x19a/0x1f0 [xfs]
    [<ffffffffa029fada>] xfs_btree_insrec+0x3aa/0x810 [xfs]
    [<ffffffffa029fff3>] xfs_btree_insert+0xb3/0x240 [xfs]
    [<ffffffffa02cb729>] xfs_rmap_insert+0x99/0x200 [xfs]
    [<ffffffffa02cf142>] xfs_rmap_map_shared+0x192/0x5f0 [xfs]
    [<ffffffffa02cf60b>] xfs_rmap_map_raw+0x6b/0x90 [xfs]
    [<ffffffffa0384a85>] xrep_rmap_stash+0xd5/0x1d0 [xfs]
    [<ffffffffa0384dc0>] xrep_rmap_visit_bmbt+0xa0/0xf0 [xfs]
    [<ffffffffa0384fb6>] xrep_rmap_scan_iext+0x56/0xa0 [xfs]
    [<ffffffffa03850d8>] xrep_rmap_scan_ifork+0xd8/0x160 [xfs]
    [<ffffffffa0385195>] xrep_rmap_scan_inode+0x35/0x80 [xfs]
    [<ffffffffa03852ee>] xrep_rmap_find_rmaps+0x10e/0x270 [xfs]

I noticed that xfs_btree_insrec has a bunch of debug code that return
out of the function immediately, without freeing the "new" btree cursor
that can be returned when _make_block_unfull calls xfs_btree_split.  Fix
the error return in this function to free the btree cursor.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

Author: Darrick J. Wong

fs/xfs/libxfs/xfs_btree.c

@@ -3272,7 +3272,7 @@ xfs_btree_insrec(
 	struct xfs_btree_block	*block;	/* btree block */
 	struct xfs_buf		*bp;	/* buffer for block */
 	union xfs_btree_ptr	nptr;	/* new block ptr */
-	struct xfs_btree_cur	*ncur;	/* new btree cursor */
+	struct xfs_btree_cur	*ncur = NULL;	/* new btree cursor */
 	union xfs_btree_key	nkey;	/* new block key */
 	union xfs_btree_key	*lkey;
 	int			optr;	/* old key/record index */
@@ -3352,7 +3352,7 @@ xfs_btree_insrec(
 #ifdef DEBUG
 	error = xfs_btree_check_block(cur, block, level, bp);
 	if (error)
-		return error;
+		goto error0;
 #endif
 
 	/*
@@ -3372,7 +3372,7 @@ xfs_btree_insrec(
 		for (i = numrecs - ptr; i >= 0; i--) {
 			error = xfs_btree_debug_check_ptr(cur, pp, i, level);
 			if (error)
-				return error;
+				goto error0;
 		}
 
 		xfs_btree_shift_keys(cur, kp, 1, numrecs - ptr + 1);
@@ -3457,6 +3457,8 @@ xfs_btree_insrec(
 	return 0;
 
 error0:
+	if (ncur)
+		xfs_btree_del_cursor(ncur, error);
 	return error;
 }