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From:   Scott Wood <swood@redhat.com>
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Paul E . McKenney" <paulmck@linux.ibm.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Clark Williams <williams@redhat.com>,
        Scott Wood <swood@redhat.com>
Subject: [PATCH RT v3 3/5] sched: migrate_dis/enable: Use rt_invol_sleep
Date:   Wed, 11 Sep 2019 17:57:27 +0100
Message-Id: <20190911165729.11178-4-swood@redhat.com>
In-Reply-To: <20190911165729.11178-1-swood@redhat.com>
References: <20190911165729.11178-1-swood@redhat.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Without this, rcu_note_context_switch() will complain if an RCU read lock
is held when migrate_enable() calls stop_one_cpu().  Likewise when
migrate_disable() calls pin_current_cpu() which calls __read_rt_lock() --
which bypasses the part of the mutex code that calls rt_invol_sleep_inc().

Signed-off-by: Scott Wood <swood@redhat.com>
---
v3: Add to pin_current_cpu as well

 include/linux/sched.h    | 4 ++--
 kernel/cpu.c             | 2 ++
 kernel/rcu/tree_plugin.h | 2 +-
 kernel/sched/core.c      | 4 ++++
 4 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index edc93b74f7d8..ecf5cbb23335 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -673,7 +673,7 @@ struct task_struct {
 	int				migrate_disable_atomic;
 # endif
 #endif
-#ifdef CONFIG_PREEMPT_RT_FULL
+#ifdef CONFIG_PREEMPT_RT_BASE
 	/* Task is blocking due to RT-specific mechanisms, not voluntarily */
 	int				rt_invol_sleep;
 #endif
@@ -1882,7 +1882,7 @@ static __always_inline bool need_resched(void)
 	return unlikely(tif_need_resched());
 }
 
-#ifdef CONFIG_PREEMPT_RT_FULL
+#ifdef CONFIG_PREEMPT_RT_BASE
 static inline void rt_invol_sleep_inc(void)
 {
 	current->rt_invol_sleep++;
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 885a195dfbe0..32c6175b63b6 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -308,7 +308,9 @@ void pin_current_cpu(void)
 	preempt_lazy_enable();
 	preempt_enable();
 
+	rt_invol_sleep_inc();
 	__read_rt_lock(cpuhp_pin);
+	rt_invol_sleep_dec();
 
 	preempt_disable();
 	preempt_lazy_disable();
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0da4b975cd71..6d92dafeeca5 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -292,7 +292,7 @@ void rcu_note_context_switch(bool preempt)
 	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	trace_rcu_utilization(TPS("Start context switch"));
 	lockdep_assert_irqs_disabled();
-#if defined(CONFIG_PREEMPT_RT_FULL)
+#if defined(CONFIG_PREEMPT_RT_BASE)
 	rt_invol = t->rt_invol_sleep;
 #endif
 	WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0 && !rt_invol);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e1bdd7f9be05..a151332474d8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7405,7 +7405,11 @@ void migrate_enable(void)
 			unpin_current_cpu();
 			preempt_lazy_enable();
 			preempt_enable();
+
+			rt_invol_sleep_inc();
 			stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
+			rt_invol_sleep_dec();
+
 			return;
 		}
 	}
-- 
1.8.3.1