[PATCH 5.0 039/346] acct_on(): dont mess with freeze protection

[Greg Kroah-Hartman]

From: Al Viro <v...@zeniv.linux.org.uk>

commit 9419a3191dcb27f24478d288abaab697228d28e6 upstream.

What happens there is that we are replacing file->path.mnt of
a file we'd just opened with a clone and we need the write
count contribution to be transferred from original mount to
new one.  That's it.  We do *NOT* want any kind of freeze
protection for the duration of switchover.

IOW, we should just use __mnt_{want,drop}_write() for that
switchover; no need to bother with mnt_{want,drop}_write()
there.

Tested-by: Amir Goldstein <amir7...@gmail.com>
Reported-by: syzbot+2a73a6ea9507b7112...@syzkaller.appspotmail.com
Signed-off-by: Al Viro <v...@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 fs/internal.h         |    2 --
 include/linux/mount.h |    2 ++
 kernel/acct.c         |    4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

--- a/fs/internal.h
+++ b/fs/internal.h
@@ -80,9 +80,7 @@ extern int sb_prepare_remount_readonly(s
 
 extern void __init mnt_init(void);
 
-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 *);
 
 /*
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -86,6 +86,8 @@ extern bool mnt_may_suid(struct vfsmount
 
 struct path;
 extern struct vfsmount *clone_private_mount(const struct path *path);
+extern int __mnt_want_write(struct vfsmount *);
+extern void __mnt_drop_write(struct vfsmount *);
 
 struct file_system_type;
 extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -227,7 +227,7 @@ static int acct_on(struct filename *path
                filp_close(file, NULL);
                return PTR_ERR(internal);
        }
-       err = mnt_want_write(internal);
+       err = __mnt_want_write(internal);
        if (err) {
                mntput(internal);
                kfree(acct);
@@ -252,7 +252,7 @@ static int acct_on(struct filename *path
        old = xchg(&ns->bacct, &acct->pin);
        mutex_unlock(&acct->lock);
        pin_kill(old);
-       mnt_drop_write(mnt);
+       __mnt_drop_write(mnt);
        mntput(mnt);
        return 0;
 }