do_io_accounting: use __for_each_thread()

JIRA: https://issues.redhat.com/browse/RHEL-105165

commit 2320222
Author: Oleg Nesterov <oleg@redhat.com>
Date:   Mon, 23 Oct 2023 17:33:43 +0200

    do_io_accounting: use __for_each_thread()

    Rather than while_each_thread() which should be avoided when possible.

    This makes the code more clear and allows the next change.

    Link: https://lkml.kernel.org/r/20231023153343.GA4629@redhat.com
    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

fs/proc/base.c

@@ -2948,7 +2948,7 @@ static const struct file_operations proc_coredump_filter_operations = {
 #ifdef CONFIG_TASK_IO_ACCOUNTING
 static int do_io_accounting(struct task_struct *task, struct seq_file *m, int whole)
 {
-	struct task_io_accounting acct = task->ioac;
+	struct task_io_accounting acct;
 	unsigned long flags;
 	int result;
 
@@ -2962,14 +2962,18 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh
 	}
 
 	if (whole && lock_task_sighand(task, &flags)) {
-		struct task_struct *t = task;
+		struct signal_struct *sig = task->signal;
+		struct task_struct *t;
 
-		task_io_accounting_add(&acct, &task->signal->ioac);
-		while_each_thread(task, t)
+		acct = sig->ioac;
+		__for_each_thread(sig, t)
 			task_io_accounting_add(&acct, &t->ioac);
 
 		unlock_task_sighand(task, &flags);
+	} else {
+		acct = task->ioac;
 	}
+
 	seq_printf(m,
 		   "rchar: %llu\n"
 		   "wchar: %llu\n"