fs: Add freezing handling to mnt_want_write() / mnt_drop_write()

Most of places where we want freeze protection coincides with the places where
we also have remount-ro protection. So make mnt_want_write() and
mnt_drop_write() (and their _file alternative) prevent freezing as well.
For the few cases that are really interested only in remount-ro protection
provide new function variants.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/internal.h b/fs/internal.h
index a6fd56c68b11..371bcc4b1697 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -61,6 +61,10 @@ extern void __init mnt_init(void);
 
 extern struct lglock vfsmount_lock;
 
+extern int __mnt_want_write(struct vfsmount *);
+extern int __mnt_want_write_file(struct file *);
+extern void __mnt_drop_write(struct vfsmount *);
+extern void __mnt_drop_write_file(struct file *);
 
 /*
  * fs_struct.c