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SubjectRe: [PATCH RT v2 2/3] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep
On Wed, Aug 21, 2019 at 06:19:05PM -0500, Scott Wood wrote:
> 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 <swood@redhat.com>

I have to ask... Both sleeping_lock_inc() and sleeping_lock_dec() are
no-ops if not CONFIG_PREEMPT_RT_BASE?

Thanx, Paul

> ---
> 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
>

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