GFS2: Fix remount argument parsing

The following patch fixes an issue relating to remount and argument
parsing. After this fix is applied, remount becomes atomic in that
it either succeeds changing the mount to the new state, or it fails
and leaves it in the old state. Previously it was possible for the
parsing of options to fail part way though and for the fs to be left
in a state where some of the new arguments had been applied, but some
had not.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 31 insertions, 10 deletions

diff --git a/fs/gfs2/ops_super.c b/fs/gfs2/ops_super.c
index 320323d0347933..f0699ac453f763 100644
--- a/fs/gfs2/ops_super.c
+++ b/fs/gfs2/ops_super.c
@@ -27,7 +27,6 @@
 #include "glock.h"
 #include "inode.h"
 #include "log.h"
-#include "mount.h"
 #include "quota.h"
 #include "recovery.h"
 #include "rgrp.h"
@@ -40,6 +39,8 @@
 #include "bmap.h"
 #include "meta_io.h"
 
+#define args_neq(a1, a2, x) ((a1)->ar_##x != (a2)->ar_##x)
+
 /**
  * gfs2_write_inode - Make sure the inode is stable on the disk
  * @inode: The inode
@@ -435,25 +436,45 @@ static int gfs2_statfs(struct dentry *dentry, struct kstatfs *buf)
 static int gfs2_remount_fs(struct super_block *sb, int *flags, char *data)
 {
 	struct gfs2_sbd *sdp = sb->s_fs_info;
+	struct gfs2_args args = sdp->sd_args; /* Default to current settings */
 	int error;
 
-	error = gfs2_mount_args(sdp, data, 1);
+	error = gfs2_mount_args(sdp, &args, data);
 	if (error)
 		return error;
 
+	/* Not allowed to change locking details */
+	if (strcmp(args.ar_lockproto, sdp->sd_args.ar_lockproto) ||
+	    strcmp(args.ar_locktable, sdp->sd_args.ar_locktable) ||
+	    strcmp(args.ar_hostdata, sdp->sd_args.ar_hostdata))
+		return -EINVAL;
+
+	/* Some flags must not be changed */
+	if (args_neq(&args, &sdp->sd_args, spectator) ||
+	    args_neq(&args, &sdp->sd_args, ignore_local_fs) ||
+	    args_neq(&args, &sdp->sd_args, localflocks) ||
+	    args_neq(&args, &sdp->sd_args, localcaching) ||
+	    args_neq(&args, &sdp->sd_args, meta))
+		return -EINVAL;
+
 	if (sdp->sd_args.ar_spectator)
 		*flags |= MS_RDONLY;
-	else {
-		if (*flags & MS_RDONLY) {
-			if (!(sb->s_flags & MS_RDONLY))
-				error = gfs2_make_fs_ro(sdp);
-		} else if (!(*flags & MS_RDONLY) &&
-			   (sb->s_flags & MS_RDONLY)) {
+
+	if ((sb->s_flags ^ *flags) & MS_RDONLY) {
+		if (*flags & MS_RDONLY)
+			error = gfs2_make_fs_ro(sdp);
+		else
 			error = gfs2_make_fs_rw(sdp);
-		}
+		if (error)
+			return error;
 	}
 
-	return error;
+	sdp->sd_args = args;
+	if (sdp->sd_args.ar_posix_acl)
+		sb->s_flags |= MS_POSIXACL;
+	else
+		sb->s_flags &= ~MS_POSIXACL;
+	return 0;
 }
 
 /**