introduce for_other_threads(p, t)

Cosmetic, but imho it makes the usage look more clear and simple, the new
helper doesn't require to initialize "t".

After this change while_each_thread() has only 3 users, and it is only
used in the do/while loops.

Link: https://lkml.kernel.org/r/20231030155710.GA9095@redhat.comSigned-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/exec.c

@@ -1578,11 +1578,10 @@ static void check_unsafe_exec(struct linux_binprm *bprm)
 	 * will be able to manipulate the current directory, etc.
 	 * It would be nice to force an unshare instead...
 	 */
-	t = p;
 	n_fs = 1;
 	spin_lock(&p->fs->lock);
 	rcu_read_lock();
-	while_each_thread(p, t) {
+	for_other_threads(p, t) {
 		if (t->fs == p->fs)
 			n_fs++;
 	}

include/linux/sched/signal.h

@@ -646,6 +646,9 @@ extern bool current_is_single_threaded(void);
 #define while_each_thread(g, t) \
 	while ((t = next_thread(t)) != g)
 
+#define for_other_threads(p, t)	\
+	for (t = p; (t = next_thread(t)) != p; )
+
 #define __for_each_thread(signal, t)	\
 	list_for_each_entry_rcu(t, &(signal)->thread_head, thread_node, \
 		lockdep_is_held(&tasklist_lock))

kernel/signal.c

@@ -1376,12 +1376,12 @@ int force_sig_info(struct kernel_siginfo *info)
  */
 int zap_other_threads(struct task_struct *p)
 {
-	struct task_struct *t = p;
+	struct task_struct *t;
 	int count = 0;
 
 	p->signal->group_stop_count = 0;
 
-	while_each_thread(p, t) {
+	for_other_threads(p, t) {
 		task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 		/* Don't require de_thread to wait for the vhost_worker */
 		if ((t->flags & (PF_IO_WORKER | PF_USER_WORKER)) != PF_USER_WORKER)
@@ -2465,12 +2465,10 @@ static bool do_signal_stop(int signr)
 			sig->group_exit_code = signr;
 
 		sig->group_stop_count = 0;
-
 		if (task_set_jobctl_pending(current, signr | gstop))
 			sig->group_stop_count++;
 
-		t = current;
-		while_each_thread(current, t) {
+		for_other_threads(current, t) {
 			/*
 			 * Setting state to TASK_STOPPED for a group
 			 * stop is always done with the siglock held,
@@ -2966,8 +2964,7 @@ static void retarget_shared_pending(struct task_struct *tsk, sigset_t *which)
 	if (sigisemptyset(&retarget))
 		return;
 
-	t = tsk;
-	while_each_thread(tsk, t) {
+	for_other_threads(tsk, t) {
 		if (t->flags & PF_EXITING)
 			continue;