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Date:   Fri,  2 Jun 2023 21:23:46 +0000
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Message-ID: <20230602212350.535358-1-jstultz@google.com>
Subject: [RESEND][PATCH v2] sched/wait: Fix a kthread_park race with wait_woken()
From:   John Stultz <jstultz@google.com>
To:     LKML <linux-kernel@vger.kernel.org>
Cc:     "=?UTF-8?q?Arve=20Hj=C3=B8nnev=C3=A5g?=" <arve@android.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        android-kernel-team <android-kernel-team@google.com>,
        John Stultz <jstultz@google.com>
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From: Arve Hj=C3=B8nnev=C3=A5g <arve@android.com>

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.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: android-kernel-team <android-kernel-team@google.com>
Signed-off-by: Arve Hj=C3=B8nnev=C3=A5g <arve@android.com>
[jstultz: Made changes suggested by Peter to optimize
 memory loads]
Signed-off-by: John Stultz <jstultz@google.com>
---
v2:
* Commit message tweaks, suggested by Peter
* Move logic to kthread.c & optimize to avoid duplicate memory
  loads, also suggested by Peter
---
 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 30e5bec81d2b..f1f95a71a4bc 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 490792b1066e..07a057086d26 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -182,6 +182,16 @@ bool kthread_should_park(void)
 }
 EXPORT_SYMBOL_GPL(kthread_should_park);
=20
+bool kthread_should_stop_or_park(void)
+{
+	struct kthread *kthread =3D __to_kthread(current);
+
+	if (!kthread)
+		return false;
+
+	return kthread->flags & (BIT(KTHREAD_SHOULD_STOP) | BIT(KTHREAD_SHOULD_PA=
RK));
+}
+
 /**
  * kthread_freezable_should_stop - should this freezable kthread return no=
w?
  * @was_frozen: optional out parameter, indicates whether %current was fro=
zen
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 133b74730738..48c53e4739ea 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);
=20
-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, unsi=
gned 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 =3D schedule_timeout(timeout);
 	__set_current_state(TASK_RUNNING);
=20
--=20
2.41.0.rc2.161.g9c6817b8e7-goog