From 83895227aba1ade33e81f586aa7b6b1e143096a5 Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <darrick.wong@oracle.com>
Date: Mon, 29 Jun 2020 14:47:18 -0700
Subject: [PATCH] xfs: fix reflink quota reservation accounting error
Git-commit: 83895227aba1ade33e81f586aa7b6b1e143096a5
Patch-mainline: v5.9-rc1
References: git-fixes

Quota reservations are supposed to account for the blocks that might be
allocated due to a bmap btree split.  Reflink doesn't do this, so fix
this to make the quota accounting more accurate before we start
rearranging things.

Fixes: 862bb360ef56 ("xfs: reflink extents from one file to another")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Acked-by: Anthony Iliopoulos <ailiop@suse.com>

---
 fs/xfs/xfs_reflink.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 107bf2a2f344..d89201d40891 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1003,6 +1003,7 @@ xfs_reflink_remap_extent(
 	xfs_filblks_t		rlen;
 	xfs_filblks_t		unmap_len;
 	xfs_off_t		newlen;
+	int64_t			qres;
 	int			error;
 
 	unmap_len = irec->br_startoff + irec->br_blockcount - destoff;
@@ -1025,13 +1026,19 @@ xfs_reflink_remap_extent(
 	xfs_ilock(ip, XFS_ILOCK_EXCL);
 	xfs_trans_ijoin(tp, ip, 0);
 
-	/* If we're not just clearing space, then do we have enough quota? */
-	if (real_extent) {
-		error = xfs_trans_reserve_quota_nblks(tp, ip,
-				irec->br_blockcount, 0, XFS_QMOPT_RES_REGBLKS);
-		if (error)
-			goto out_cancel;
-	}
+	/*
+	 * Reserve quota for this operation.  We don't know if the first unmap
+	 * in the dest file will cause a bmap btree split, so we always reserve
+	 * at least enough blocks for that split.  If the extent being mapped
+	 * in is written, we need to reserve quota for that too.
+	 */
+	qres = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
+	if (real_extent)
+		qres += irec->br_blockcount;
+	error = xfs_trans_reserve_quota_nblks(tp, ip, qres, 0,
+			XFS_QMOPT_RES_REGBLKS);
+	if (error)
+		goto out_cancel;
 
 	trace_xfs_reflink_remap(ip, irec->br_startoff,
 				irec->br_blockcount, irec->br_startblock);
-- 
2.28.0