fs: distinguish between user initiated freeze and kernel initiated freeze

Userspace can freeze a filesystem using the FIFREEZE ioctl or by
suspending the block device; this state persists until userspace thaws
the filesystem with the FITHAW ioctl or resuming the block device.
Since commit 18e9e5104fcd ("Introduce freeze_super and thaw_super for
the fsfreeze ioctl") we only allow the first freeze command to succeed.

The kernel may decide that it is necessary to freeze a filesystem for
its own internal purposes, such as suspends in progress, filesystem fsck
activities, or quiescing a device prior to removal.  Userspace thaw
commands must never break a kernel freeze, and kernel thaw commands
shouldn't undo userspace's freeze command.

Introduce a couple of freeze holder flags and wire it into the
sb_writers state.  One kernel and one userspace freeze are allowed to
coexist at the same time; the filesystem will not thaw until both are
lifted.

I wonder if the f2fs/gfs2 code should be using a kernel freeze here, but
for now we'll use FREEZE_HOLDER_USERSPACE to preserve existing
behaviors.

Cc: mcgrof@kernel.org
Cc: jack@suse.cz
Cc: hch@infradead.org
Cc: ruansy.fnst@fujitsu.com
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>

1 files changed, 5 insertions, 3 deletions

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 01effd3fcb6c..a1ca394bc327 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -2181,12 +2181,14 @@ out_drop_write:
 	if (err)
 		return err;
 
-	err = freeze_super(sbi->sb);
+	err = freeze_super(sbi->sb, FREEZE_HOLDER_USERSPACE);
 	if (err)
 		return err;
 
 	if (f2fs_readonly(sbi->sb)) {
-		thaw_super(sbi->sb);
+		err = thaw_super(sbi->sb, FREEZE_HOLDER_USERSPACE);
+		if (err)
+			return err;
 		return -EROFS;
 	}
 
@@ -2240,6 +2242,6 @@ recover_out:
 out_err:
 	f2fs_up_write(&sbi->cp_global_sem);
 	f2fs_up_write(&sbi->gc_lock);
-	thaw_super(sbi->sb);
+	thaw_super(sbi->sb, FREEZE_HOLDER_USERSPACE);
 	return err;
 }