gfs2: move freeze glock outside the make_fs_rw and _ro functions

Before this patch, sister functions gfs2_make_fs_rw and gfs2_make_fs_ro locked
(held) the freeze glock by calling gfs2_freeze_lock and gfs2_freeze_unlock.
The problem is, not all the callers of gfs2_make_fs_ro should be doing this.
The three callers of gfs2_make_fs_ro are: remount (gfs2_reconfigure),
signal_our_withdraw, and unmount (gfs2_put_super). But when unmounting the
file system we can get into the following circular lock dependency:

deactivate_super
   down_write(&s->s_umount); <-------------------------------------- s_umount
   deactivate_locked_super
      gfs2_kill_sb
         kill_block_super
            generic_shutdown_super
               gfs2_put_super
                  gfs2_make_fs_ro
                     gfs2_glock_nq_init sd_freeze_gl
                        freeze_go_sync
                           if (freeze glock in SH)
                              freeze_super (vfs)
                                 down_write(&sb->s_umount); <------- s_umount

This patch moves the hold of the freeze glock outside the two sister rw/ro
functions to their callers, but it doesn't request the glock from
gfs2_put_super, thus eliminating the circular dependency.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

1 files changed, 17 insertions, 14 deletions

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 4ee56f5e93cb..f2c6bbe5cdb8 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1084,6 +1084,7 @@ static int gfs2_fill_super(struct super_block *sb, struct fs_context *fc)
 	int silent = fc->sb_flags & SB_SILENT;
 	struct gfs2_sbd *sdp;
 	struct gfs2_holder mount_gh;
+	struct gfs2_holder freeze_gh;
 	int error;
 
 	sdp = init_sbd(sb);
@@ -1195,23 +1196,18 @@ static int gfs2_fill_super(struct super_block *sb, struct fs_context *fc)
 		goto fail_per_node;
 	}
 
-	if (sb_rdonly(sb)) {
-		struct gfs2_holder freeze_gh;
+	error = gfs2_freeze_lock(sdp, &freeze_gh, 0);
+	if (error)
+		goto fail_per_node;
 
-		error = gfs2_freeze_lock(sdp, &freeze_gh, 0);
-		if (error) {
-			fs_err(sdp, "can't make FS RO: %d\n", error);
-			goto fail_per_node;
-		}
-		gfs2_freeze_unlock(&freeze_gh);
-	} else {
+	if (!sb_rdonly(sb))
 		error = gfs2_make_fs_rw(sdp);
-		if (error) {
-			fs_err(sdp, "can't make FS RW: %d\n", error);
-			goto fail_per_node;
-		}
-	}
 
+	gfs2_freeze_unlock(&freeze_gh);
+	if (error) {
+		fs_err(sdp, "can't make FS RW: %d\n", error);
+		goto fail_per_node;
+	}
 	gfs2_glock_dq_uninit(&mount_gh);
 	gfs2_online_uevent(sdp);
 	return 0;
@@ -1512,6 +1508,12 @@ static int gfs2_reconfigure(struct fs_context *fc)
 		fc->sb_flags |= SB_RDONLY;
 
 	if ((sb->s_flags ^ fc->sb_flags) & SB_RDONLY) {
+		struct gfs2_holder freeze_gh;
+
+		error = gfs2_freeze_lock(sdp, &freeze_gh, 0);
+		if (error)
+			return -EINVAL;
+
 		if (fc->sb_flags & SB_RDONLY) {
 			error = gfs2_make_fs_ro(sdp);
 			if (error)
@@ -1521,6 +1523,7 @@ static int gfs2_reconfigure(struct fs_context *fc)
 			if (error)
 				errorfc(fc, "unable to remount read-write");
 		}
+		gfs2_freeze_unlock(&freeze_gh);
 	}
 	sdp->sd_args = *newargs;