From 75b7d18603920886787998652364d184946c1b0e Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Thu, 17 Aug 2023 18:37:08 +0200
Subject: [PATCH] kill do_each_thread()

References: bsc#1214683 (PREEMPT_RT prerequisite backports)
Patch-mainline: v6.6-rc1
Git-commit: 5ffd2c37cb7a53d52099e5ed1fd7ccbc9e358791

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>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 arch/ia64/kernel/mca.c       | 4 ++--
 drivers/tty/tty_io.c         | 4 ++--
 fs/fs_struct.c               | 4 ++--
 include/linux/sched/signal.h | 7 -------
 4 files changed, 6 insertions(+), 13 deletions(-)

diff --git a/arch/ia64/kernel/mca.c b/arch/ia64/kernel/mca.c
index 92ede80d17fe..2671688d349a 100644
--- a/arch/ia64/kernel/mca.c
+++ b/arch/ia64/kernel/mca.c
@@ -1630,10 +1630,10 @@ default_monarch_init_process(struct notifier_block *self, unsigned long val, voi
 	}
 	printk("\n\n");
 	if (read_trylock(&tasklist_lock)) {
-		do_each_thread (g, t) {
+		for_each_process_thread(g, t) {
 			printk("\nBacktrace of pid %d (%s)\n", t->pid, t->comm);
 			show_stack(t, NULL, KERN_DEFAULT);
-		} while_each_thread (g, t);
+		}
 		read_unlock(&tasklist_lock);
 	}
 	/* FIXME: This will not restore zapped printk locks. */
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 68795761b76e..0b7dc62a32c8 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3021,7 +3021,7 @@ void __do_SAK(struct tty_struct *tty)
 	} while_each_pid_task(session, PIDTYPE_SID, p);
 
 	/* Now kill any processes that happen to have the tty open */
-	do_each_thread(g, p) {
+	for_each_process_thread(g, p) {
 		if (p->signal->tty == tty) {
 			tty_notice(tty, "SAK: killed process %d (%s): by controlling tty\n",
 				   task_pid_nr(p), p->comm);
@@ -3038,7 +3038,7 @@ void __do_SAK(struct tty_struct *tty)
 					PIDTYPE_SID);
 		}
 		task_unlock(p);
-	} while_each_thread(g, p);
+	}
 	read_unlock(&tasklist_lock);
 	put_pid(session);
 }
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);
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index ef20447727c1..70e589cf1b01 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -649,13 +649,6 @@ extern void flush_itimer_signals(void);
 
 extern bool current_is_single_threaded(void);
 
-/*
- * Careful: do_each_thread/while_each_thread is a double loop so
- *          'break' will not work as expected - use goto instead.
- */
-#define do_each_thread(g, t) \
-	for (g = t = &init_task ; (g = t = next_task(g)) != &init_task ; ) do
-
 #define while_each_thread(g, t) \
 	while ((t = next_thread(t)) != g)