linux-kernel - [PATCH] kernel/sched/wait.c: set timeout to 0 when kthread should stop

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Date:   Mon, 11 May 2020 23:50:21 -0400
From:   Qingjie Xing <xqjcool@...il.com>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org
Cc:     dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, linux-kernel@...r.kernel.org,
        Qingjie Xing <xqjcool@...il.com>
Subject: [PATCH] kernel/sched/wait.c: set timeout to 0 when kthread should stop

Using kthread_stop() to terminate a thread causes tcp_recvmsg()
to enter a dead loop when the kernel thread uses tcp_recvmsg()
to receive a message.

tcp_recvmsg()-->sk_wait_data()-->sk_wait_event()-->wait_woken().

wait_woken() will directly return unchanged timeout value rather
than be executed as normally.

tcp_recvmsg () will continues to execute sk_wait_data(). So finally
this situation will creat an endless loop that cannot be exited.

Signed-off-by: Qingjie Xing <xqjcool@...il.com>
---
 kernel/sched/wait.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index ba059fb..a27bbbd 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -431,6 +431,8 @@ long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
 	set_current_state(mode); /* A */
 	if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
 		timeout = schedule_timeout(timeout);
+	if (is_kthread_should_stop())
+		timeout = 0;
 	__set_current_state(TASK_RUNNING);
 
 	/*
-- 
1.8.3.1