coredump: change zap_threads() and zap_process() to use for_each_thread()

Change zap_threads() paths to use for_each_thread() rather than
while_each_thread().

While at it, change zap_threads() to avoid the nested if's to make the
code more readable and lessen the indentation.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Kyle Walker <kwalker@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Stanislav Kozina <skozina@redhat.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/coredump.c

@@ -290,15 +290,14 @@ static int zap_process(struct task_struct *start, int exit_code, int flags)
 	start->signal->group_exit_code = exit_code;
 	start->signal->group_stop_count = 0;
 
-	t = start;
-	do {
+	for_each_thread(start, t) {
 		task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 		if (t != current && t->mm) {
 			sigaddset(&t->pending.signal, SIGKILL);
 			signal_wake_up(t, 1);
 			nr++;
 		}
-	} while_each_thread(start, t);
+	}
 
 	return nr;
 }
@@ -360,9 +359,10 @@ static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 			continue;
 		if (g->flags & PF_KTHREAD)
 			continue;
-		p = g;
-		do {
-			if (p->mm) {
+
+		for_each_thread(g, p) {
+			if (unlikely(!p->mm))
+				continue;
 			if (unlikely(p->mm == mm)) {
 				lock_task_sighand(p, &flags);
 				nr += zap_process(p, exit_code,
@@ -371,7 +371,6 @@ static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 			}
 			break;
 		}
-		} while_each_thread(g, p);
 	}
 	rcu_read_unlock();
 done: