nfs: don't lose MS_SYNCHRONOUS on remount of noac mount

commit 26c4c170731f00008f4317a2888a0a07ac99d90d upstream.

On a remount, the VFS layer will clear the MS_SYNCHRONOUS bit on the
assumption that the flags on the mount syscall will have it set if the
remounted fs is supposed to keep it.

In the case of "noac" though, MS_SYNCHRONOUS is implied. A remount of
such a mount will lose the MS_SYNCHRONOUS flag since "sync" isn't part
of the mount options.

Reported-by: Max Matveev <makc@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index c0173a8531e212d8a473221c48f4ec363252c6d9..c34680849c5290199a91d42bf276dc6f9d20e01e 100644 (file)
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -1925,6 +1925,15 @@ nfs_remount(struct super_block *sb, int *flags, char *raw_data)
        if (error < 0)
                goto out;
 
+       /*
+        * noac is a special case. It implies -o sync, but that's not
+        * necessarily reflected in the mtab options. do_remount_sb
+        * will clear MS_SYNCHRONOUS if -o sync wasn't specified in the
+        * remount options, so we have to explicitly reset it.
+        */
+       if (data->flags & NFS_MOUNT_NOAC)
+               *flags |= MS_SYNCHRONOUS;
+
        /* compare new mount options with old ones */
        error = nfs_compare_remount_data(nfss, data);
 out: