[PATCH 6.1 4/6] xfs: short circuit xfs_growfs_data_private() if delta is zero

[Mahmoud Adam <mngyadam@amazon.com>]

From: Eric Sandeen <sandeen@redhat.com>

commit 84712492e6dab803bf595fb8494d11098b74a652 upstream.

Although xfs_growfs_data() doesn't call xfs_growfs_data_private()
if in->newblocks == mp->m_sb.sb_dblocks, xfs_growfs_data_private()
further massages the new block count so that we don't i.e. try
to create a too-small new AG.

This may lead to a delta of "0" in xfs_growfs_data_private(), so
we end up in the shrink case and emit the EXPERIMENTAL warning
even if we're not changing anything at all.

Fix this by returning straightaway if the block delta is zero.

(nb: in older kernels, the result of entering the shrink case
with delta == 0 may actually let an -ENOSPC escape to userspace,
which is confusing for users.)

Fixes: fb2fc1720185 ("xfs: support shrinking unused space in the last AG")
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
Signed-off-by: Mahmoud Adam <mngyadam@amazon.com>
---
 fs/xfs/xfs_fsops.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 13851c0d640b..332da0d7b85c 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -129,6 +129,10 @@ xfs_growfs_data_private(
 	if (delta < 0 && nagcount < 2)
 		return -EINVAL;

+	/* No work to do */
+	if (delta == 0)
+		return 0;
+
 	oagcount = mp->m_sb.sb_agcount;
 	/* allocate the new per-ag structures */
 	if (nagcount > oagcount) {
--
2.40.1