Re: [PATCH RT v2 2/3] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep
From: Sebastian Andrzej Siewior
Date: Fri Aug 23 2019 - 12:20:28 EST
On 2019-08-21 18:19:05 [-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@xxxxxxxxxx>
> ---
> 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(-)
>
> --- 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();
this looks like an ugly hack. This sleeping_lock_inc() is used where we
actually hold a sleeping lock and schedule() which is okay. But this
would mean we hold a RCU lock and schedule() anyway. Is that okay?
> +
> return;
> }
> }
Sebastian