Hi Brian,

On Tue, Feb 02, 2021 at 02:38:04PM -0500, Brian Foster wrote:

On Tue, Jan 26, 2021 at 08:56:17PM +0800, Gao Xiang wrote:

quoted

sb_fdblocks will be updated lazily if lazysbcount is enabled,
therefore when shrinking the filesystem sb_fdblocks could be
larger than sb_dblocks and xfs_validate_sb_write() would fail.

Even for growfs case, it'd be better to update lazy sb counters
immediately to reflect the real sb counters.

Signed-off-by: Gao Xiang <redacted>
---
 fs/xfs/xfs_fsops.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index a2a407039227..2e490fb75832 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c

@@ -128,6 +128,14 @@ xfs_growfs_data_private(
 				 nb - mp->m_sb.sb_dblocks);
 	if (id.nfree)
 		xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, id.nfree);
+
+	/*
+	 * update in-core counters now to reflect the real numbers
+	 * (especially sb_fdblocks)
+	 */

Could you update the comment to explain why we do this? For example:

"Sync sb counters now to reflect the updated values. This is
particularly important for shrink because the write verifier will fail
if sb_fdblocks is ever larger than sb_dblocks."

Thanks for the review/suggestion!

I updated the comment in "[PATCH v6 6/7] xfs: support shrinking unused
space in the last AG", since shrinking functionality is somewhat landed
after [PATCH 6/7]... If that looks worse than changing directly here,
I will shift/update the comment in the next version.

Thanks,
Gao Xiang

Brian