kill do_each_thread()

Eric has pointed out that we still have 3 users of do_each_thread().
Change them to use for_each_process_thread() and kill this helper.

There is a subtle change, after do_each_thread/while_each_thread g == t ==
&init_task, while after for_each_process_thread() they both point to
nowhere, but this doesn't matter.

> Why is for_each_process_thread() better than do_each_thread()?

Say, for_each_process_thread() is rcu safe, do_each_thread() is not.

And certainly

	for_each_process_thread(p, t) {
		do_something(p, t);
	}

looks better than

	do_each_thread(p, t) {
		do_something(p, t);
	} while_each_thread(p, t);

And again, there are only 3 users of this awkward helper left.  It should
have been killed years ago and in fact I thought it had already been
killed.  It uses while_each_thread() which needs some changes.

Link: https://lkml.kernel.org/r/20230817163708.GA8248@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: "Christian Brauner (Microsoft)" <brauner@kernel.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jiri Slaby <jirislaby@kernel.org> # tty/serial
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index 04b3f5b9c629..64c2d0814ed6 100644
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -62,7 +62,7 @@ void chroot_fs_refs(const struct path *old_root, const struct path *new_root)
 	int count = 0;
 
 	read_lock(&tasklist_lock);
-	do_each_thread(g, p) {
+	for_each_process_thread(g, p) {
 		task_lock(p);
 		fs = p->fs;
 		if (fs) {
@@ -79,7 +79,7 @@ void chroot_fs_refs(const struct path *old_root, const struct path *new_root)
 			spin_unlock(&fs->lock);
 		}
 		task_unlock(p);
-	} while_each_thread(g, p);
+	}
 	read_unlock(&tasklist_lock);
 	while (count--)
 		path_put(old_root);