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From:   Wander Lairson Costa <wander@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
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        Adrian Hunter <adrian.hunter@intel.com>,
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        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Wander Lairson Costa <wander@redhat.com>,
        "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>,
        Oleg Nesterov <oleg@redhat.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
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        SUBSYSTEM)
Cc:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [PATCH v6 1/3] sched/core: warn on call put_task_struct in invalid context
Date:   Fri, 14 Apr 2023 09:55:27 -0300
Message-Id: <20230414125532.14958-2-wander@redhat.com>
In-Reply-To: <20230414125532.14958-1-wander@redhat.com>
References: <20230414125532.14958-1-wander@redhat.com>
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Under PREEMPT_RT, spinlocks become sleepable locks. put_task_struct()
indirectly acquires a spinlock. Therefore, it can't be called in
atomic/interrupt context in RT kernels.

To prevent such conditions, add a check for atomic/interrupt context
before calling put_task_struct().

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/sched/task.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 357e0068497c..b597b97b1f8f 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -113,14 +113,28 @@ static inline struct task_struct *get_task_struct(struct task_struct *t)
 
 extern void __put_task_struct(struct task_struct *t);
 
+#define PUT_TASK_RESCHED_OFFSETS \
+	(rcu_preempt_depth() << MIGHT_RESCHED_RCU_SHIFT)
+
+#define __put_task_might_resched() \
+	__might_resched(__FILE__, __LINE__, PUT_TASK_RESCHED_OFFSETS)
+
+#define put_task_might_resched()			\
+	do {						\
+		if (IS_ENABLED(CONFIG_PREEMPT_RT))	\
+			__put_task_might_resched();	\
+	} while (0)
+
 static inline void put_task_struct(struct task_struct *t)
 {
+	put_task_might_resched();
 	if (refcount_dec_and_test(&t->usage))
 		__put_task_struct(t);
 }
 
 static inline void put_task_struct_many(struct task_struct *t, int nr)
 {
+	put_task_might_resched();
 	if (refcount_sub_and_test(nr, &t->usage))
 		__put_task_struct(t);
 }
-- 
2.39.2