[PATCH RT v2 2/3] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep

[Scott Wood]

Without this, rcu_note_context_switch() will complain if an RCU read
lock is held when migrate_enable() calls stop_one_cpu().

Signed-off-by: Scott Wood <sw...@redhat.com>
---
v2: Added comment.

If my migrate disable changes aren't taken, then pin_current_cpu()
will also need to use sleeping_lock_inc() because calling
__read_rt_lock() bypasses the usual place it's done.

 include/linux/sched.h    | 4 ++--
 kernel/rcu/tree_plugin.h | 2 +-
 kernel/sched/core.c      | 8 ++++++++
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7e892e727f12..1ebc97f28009 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
        int                             sleeping_lock;
 #endif
 
@@ -1881,7 +1881,7 @@ 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 sleeping_lock_inc(void)
 {
        current->sleeping_lock++;
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 23a54e4b649c..7a3aa085ce2c 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)
        sleeping_l = t->sleeping_lock;
 #endif
        WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0 && !sleeping_l);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e1bdd7f9be05..0758ee85634e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7405,7 +7405,15 @@ void migrate_enable(void)
                        unpin_current_cpu();
                        preempt_lazy_enable();
                        preempt_enable();
+
+                       /*
+                        * sleeping_lock_inc suppresses a debug check for
+                        * sleeping inside an RCU read side critical section
+                        */
+                       sleeping_lock_inc();
                        stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
+                       sleeping_lock_dec();
+
                        return;
                }
        }
-- 
1.8.3.1