linux-kernel - [tip: sched/core] sched/wait: Fix a kthread_park race with wait

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Date:   Fri, 16 Jun 2023 15:16:41 -0000
From:   tip-bot2 for Arve Hjønnevåg 
        <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     arve@...roid.com, John Stultz <jstultz@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/wait: Fix a kthread_park race with wait_woken()

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     ef73d6a4ef0b35524125c3cfc6deafc26a0c966a
Gitweb:        https://git.kernel.org/tip/ef73d6a4ef0b35524125c3cfc6deafc26a0c966a
Author:        Arve Hjønnevåg <arve@...roid.com>
AuthorDate:    Fri, 02 Jun 2023 21:23:46 
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 16 Jun 2023 17:08:01 +02:00

sched/wait: Fix a kthread_park race with wait_woken()

kthread_park and wait_woken have a similar race that
kthread_stop and wait_woken used to have before it was fixed in
commit cb6538e740d7 ("sched/wait: Fix a kthread race with
wait_woken()"). Extend that fix to also cover kthread_park.

[jstultz: Made changes suggested by Peter to optimize
 memory loads]

Signed-off-by: Arve Hjønnevåg <arve@...roid.com>
Signed-off-by: John Stultz <jstultz@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Valentin Schneider <vschneid@...hat.com>
Link: https://lore.kernel.org/r/20230602212350.535358-1-jstultz@google.com
---
 include/linux/kthread.h |  1 +
 kernel/kthread.c        | 10 ++++++++++
 kernel/sched/wait.c     |  7 +------
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 30e5bec..f1f95a7 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -89,6 +89,7 @@ int kthread_stop(struct task_struct *k);
 bool kthread_should_stop(void);
 bool kthread_should_park(void);
 bool __kthread_should_park(struct task_struct *k);
+bool kthread_should_stop_or_park(void);
 bool kthread_freezable_should_stop(bool *was_frozen);
 void *kthread_func(struct task_struct *k);
 void *kthread_data(struct task_struct *k);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 490792b..07a0570 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -182,6 +182,16 @@ bool kthread_should_park(void)
 }
 EXPORT_SYMBOL_GPL(kthread_should_park);
 
+bool kthread_should_stop_or_park(void)
+{
+	struct kthread *kthread = __to_kthread(current);
+
+	if (!kthread)
+		return false;
+
+	return kthread->flags & (BIT(KTHREAD_SHOULD_STOP) | BIT(KTHREAD_SHOULD_PARK));
+}
+
 /**
  * kthread_freezable_should_stop - should this freezable kthread return now?
  * @was_frozen: optional out parameter, indicates whether %current was frozen
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 133b747..48c53e4 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -425,11 +425,6 @@ int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, i
 }
 EXPORT_SYMBOL(autoremove_wake_function);
 
-static inline bool is_kthread_should_stop(void)
-{
-	return (current->flags & PF_KTHREAD) && kthread_should_stop();
-}
-
 /*
  * DEFINE_WAIT_FUNC(wait, woken_wake_func);
  *
@@ -459,7 +454,7 @@ long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
 	 * or woken_wake_function() sees our store to current->state.
 	 */
 	set_current_state(mode); /* A */
-	if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
+	if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !kthread_should_stop_or_park())
 		timeout = schedule_timeout(timeout);
 	__set_current_state(TASK_RUNNING);