On Tue, Sep 17, 2013 at 04:40:12PM +0200, Peter Zijlstra wrote:
> Thomas Meyer reported a UP build fail, should be fixed.
>
> ---
> Subject: sched, rcu: Make RCU use resched_cpu()
> From: Peter Zijlstra <pet...@infradead.org>
> Date: Tue Sep 17 09:30:55 CEST 2013
>
> We're going to deprecate and remove set_need_resched() for it will do
> the wrong thing. Make an exception for RCU and allow it to use
> resched_cpu() which will do the right thing.
>
> Cc: Paul McKenney <paul...@linux.vnet.ibm.com>
> Signed-off-by: Peter Zijlstra <pet...@infradead.org>
Queued for 3.13, thank you!
Thanx, Paul
> ---
> kernel/rcutree.c | 15 ++++++++++++++-
> kernel/sched/core.c | 10 ++--------
> 2 files changed, 16 insertions(+), 9 deletions(-)
>
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -898,6 +898,12 @@ static void print_other_cpu_stall(struct
> force_quiescent_state(rsp); /* Kick them all. */
> }
>
> +/*
> + * This function really isn't for public consumption, but RCU is special in
> + * that context switches can allow the state machine to make progress.
> + */
> +extern void resched_cpu(int cpu);
> +
> static void print_cpu_stall(struct rcu_state *rsp)
> {
> int cpu;
> @@ -927,7 +933,14 @@ static void print_cpu_stall(struct rcu_s
> 3 * rcu_jiffies_till_stall_check() + 3;
> raw_spin_unlock_irqrestore(&rnp->lock, flags);
>
> - set_need_resched(); /* kick ourselves to get things going. */
> + /*
> + * Attempt to revive the RCU machinery by forcing a context switch.
> + *
> + * A context switch would normally allow the RCU state machine to make
> + * progress and it could be we're stuck in kernel space without context
> + * switches for an entirely unreasonable amount of time.
> + */
> + resched_cpu(smp_processor_id());
> }
>
> static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -513,12 +513,11 @@ static inline void init_hrtick(void)
> * might also involve a cross-CPU call to trigger the scheduler on
> * the target CPU.
> */
> -#ifdef CONFIG_SMP
> void resched_task(struct task_struct *p)
> {
> int cpu;
>
> - assert_raw_spin_locked(&task_rq(p)->lock);
> + lockdep_assert_held(&task_rq(p)->lock);
>
> if (test_tsk_need_resched(p))
> return;
> @@ -546,6 +545,7 @@ void resched_cpu(int cpu)
> raw_spin_unlock_irqrestore(&rq->lock, flags);
> }
>
> +#ifdef CONFIG_SMP
> #ifdef CONFIG_NO_HZ_COMMON
> /*
> * In the semi idle case, use the nearest busy cpu for migrating timers
> @@ -693,12 +693,6 @@ void sched_avg_update(struct rq *rq)
> }
> }
>
> -#else /* !CONFIG_SMP */
> -void resched_task(struct task_struct *p)
> -{
> - assert_raw_spin_locked(&task_rq(p)->lock);
> - set_tsk_need_resched(p);
> -}
> #endif /* CONFIG_SMP */
>
> #if defined(CONFIG_RT_GROUP_SCHED) || (defined(CONFIG_FAIR_GROUP_SCHED) && \
>
>
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