linux-kernel - [PATCH 2/2] hung_task: change check_hung_uninterruptible_tasks() to use for_each_process_thread

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Date:   Wed, 12 Sep 2018 18:33:57 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] hung_task: change check_hung_uninterruptible_tasks() to
 use for_each_process_thread_break/continue

Change check_hung_uninterruptible_tasks() to use the new helpers and remove
the "can_cont" logic from rcu_lock_break().

We could add for_each_process_thread_break/continue right into rcu_lock_break()
but see the next patch.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/hung_task.c | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index b9132d1..13af558 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -148,20 +148,11 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
  * to exit the grace period. For classic RCU, a reschedule is required.
  */
-static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
+static void rcu_lock_break(void)
 {
-	bool can_cont;
-
-	get_task_struct(g);
-	get_task_struct(t);
 	rcu_read_unlock();
 	cond_resched();
 	rcu_read_lock();
-	can_cont = pid_alive(g) && pid_alive(t);
-	put_task_struct(t);
-	put_task_struct(g);
-
-	return can_cont;
 }
 
 /*
@@ -185,16 +176,18 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 	hung_task_show_lock = false;
 	rcu_read_lock();
 	for_each_process_thread(g, t) {
-		if (!max_count--)
+		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
+		if (t->state == TASK_UNINTERRUPTIBLE)
+			check_hung_task(t, timeout);
+
+		if (!--max_count)
 			goto unlock;
 		if (!--batch_count) {
 			batch_count = HUNG_TASK_BATCHING;
-			if (!rcu_lock_break(g, t))
-				goto unlock;
+			for_each_process_thread_break(g, t);
+			rcu_lock_break();
+			for_each_process_thread_continue(&g, &t);
 		}
-		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
-		if (t->state == TASK_UNINTERRUPTIBLE)
-			check_hung_task(t, timeout);
 	}
  unlock:
 	rcu_read_unlock();
-- 
2.5.0