Re: [PATCH tip/core/rcu 11/20] sched,rcu: Make cond_resched() provide RCU quiescent state

[Josh Triplett]

On Sat, Jan 14, 2017 at 01:13:12AM -0800, Paul E. McKenney wrote:
> There is some confusion as to which of cond_resched() or
> cond_resched_rcu_qs() should be added to long in-kernel loops.
> This commit therefore eliminates the decision by adding RCU
> quiescent states to cond_resched().
> 
> Warning: This is a prototype.  For example, it does not correctly
> handle Tasks RCU.  Which is OK for the moment, given that no one
> actually uses Tasks RCU yet.
> 
> Reported-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Not-yet-signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Do you intend to merge this patch, or have you just posted it for
review?

You may want to remove it from this 20-patch series and post it as a
separate RFC PATCH, to ensure that it doesn't get merged while still a
prototype.

>  include/linux/sched.h | 3 ++-
>  kernel/sched/core.c   | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 4d1905245c7a..1531c48f56e2 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -3352,10 +3352,11 @@ static inline int signal_pending_state(long state, struct task_struct *p)
>   * cond_resched_lock() will drop the spinlock before scheduling,
>   * cond_resched_softirq() will enable bhs before scheduling.
>   */
> +void rcu_all_qs(void);
>  #ifndef CONFIG_PREEMPT
>  extern int _cond_resched(void);
>  #else
> -static inline int _cond_resched(void) { return 0; }
> +static inline int _cond_resched(void) { rcu_all_qs(); return 0; }
>  #endif
>  
>  #define cond_resched() ({			\
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c56fb57f2991..b442f8918eb9 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4907,6 +4907,7 @@ int __sched _cond_resched(void)
>  		preempt_schedule_common();
>  		return 1;
>  	}
> +	rcu_all_qs();
>  	return 0;
>  }
>  EXPORT_SYMBOL(_cond_resched);
> -- 
> 2.5.2
>