[PATCH] NFS: invalidate i_blocks after COMMIT to fix stale block count on NFSv4

NFSv4 COMMIT compound does not include GETATTR, and nfs4_commit_done_cb
does not refresh inode attributes. Meanwhile, every WRITE marks
NFS_INO_INVALID_BLOCKS via nfs_post_op_update_inode_force_wcc_locked.

After COMMIT, i_blocks remains stale until the next stat() triggers a
full revalidation. In writeback-heavy workloads where COMMITs happen
without intervening stat() calls, the cached block count can stay
indefinitely wrong.

Mark NFS_INO_INVALID_BLOCKS on successful COMMIT completion so that the
next nfs_getattr requesting STATX_BLOCKS will issue a GETATTR with
SPACE_USED, fetching the correct value from the server.

This matches NFSv3 behavior where nfs3_commit_done already calls
nfs_refresh_inode with the wcc_data post-op attributes.

Reproduce with xfstests generic/694 on NFSv4.0 loopback:

  Server:
    mount /dev/vdc /data/test
    mount /dev/vdd /data/scratch
    exportfs -o insecure,rw,sync,no_root_squash,fsid=1 127.0.0.1:/data/test
    exportfs -o insecure,rw,sync,no_root_squash,fsid=2 127.0.0.1:/data/scratch

  Client:
    mount -t nfs -o vers=4.0 localhost:/data/test /mnt/test
    mount -t nfs -o vers=4.0 localhost:/data/scratch /mnt/scratch

  local.config:
    export TEST_FS_MOUNT_OPTS="-o vers=4.0"
    export MOUNT_OPTIONS="-o vers=4.0"
    export FSTYP=nfs
    export TEST_DEV=localhost:/data/test
    export SCRATCH_DEV=localhost:/data/scratch
    export TEST_DIR=/mnt/test
    export SCRATCH_MNT=/mnt/scratch

This fixes xfstests generic/694.

Assisted-by: Qoder:Qwen3.7-Max
Signed-off-by: Jingbo Xu <jefflexu-KPsoFbNs7GizrGE5bRqYAgC/[email protected]>
---
 fs/nfs/write.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index d7c399763ad9..88c5c9f7434c 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1851,6 +1851,8 @@ static void nfs_commit_release_pages(struct nfs_commit_data *data)
 		/* Latency breaker */
 		cond_resched();
 	}
+	if (status >= 0)
+		nfs_set_cache_invalid(data->inode, NFS_INO_INVALID_BLOCKS);
 
 	nfs_init_cinfo(&cinfo, data->inode, data->dreq);
 	nfs_commit_end(cinfo.mds);
-- 
2.19.1.6.gb485710b