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Message-ID: <1fb673c1-d1a8-6958-65f7-a3df28a78a1c@quicinc.com>
Date:   Tue, 19 Jul 2022 15:05:11 +0530
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Subject: Re: [PATCH rcu 5/7] rcu: Add nocb_cb_kthread check to
 rcu_is_callbacks_kthread()
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To:     "Paul E. McKenney" <paulmck@kernel.org>, <rcu@vger.kernel.org>
CC:     <linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
        <rostedt@goodmis.org>, Zqiang <qiang1.zhang@intel.com>,
        kernel test robot <lkp@intel.com>
References: <20220620224455.GA3840881@paulmck-ThinkPad-P17-Gen-1>
 <20220620224503.3841196-5-paulmck@kernel.org>
From:   Neeraj Upadhyay <quic_neeraju@quicinc.com>
In-Reply-To: <20220620224503.3841196-5-paulmck@kernel.org>
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On 6/21/2022 4:15 AM, Paul E. McKenney wrote:
> From: Zqiang <qiang1.zhang@intel.com>
> 
> Callbacks are invoked in RCU kthreads when calbacks are offloaded
> (rcu_nocbs boot parameter) or when RCU's softirq handler has been
> offloaded to rcuc kthreads (use_softirq==0).  The current code allows
> for the rcu_nocbs case but not the use_softirq case.  This commit adds
> support for the use_softirq case.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> ---


Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>


Thanks
Neeraj

>   kernel/rcu/tree.c        |  4 ++--
>   kernel/rcu/tree.h        |  2 +-
>   kernel/rcu/tree_plugin.h | 33 +++++++++++++++++++--------------
>   3 files changed, 22 insertions(+), 17 deletions(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index c25ba442044a6..74455671e6cf2 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2530,7 +2530,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
>   		trace_rcu_batch_end(rcu_state.name, 0,
>   				    !rcu_segcblist_empty(&rdp->cblist),
>   				    need_resched(), is_idle_task(current),
> -				    rcu_is_callbacks_kthread());
> +				    rcu_is_callbacks_kthread(rdp));
>   		return;
>   	}
>   
> @@ -2608,7 +2608,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
>   	rcu_nocb_lock_irqsave(rdp, flags);
>   	rdp->n_cbs_invoked += count;
>   	trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
> -			    is_idle_task(current), rcu_is_callbacks_kthread());
> +			    is_idle_task(current), rcu_is_callbacks_kthread(rdp));
>   
>   	/* Update counts and requeue any remaining callbacks. */
>   	rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index 4f8532c33558f..649ad4f0129b1 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -426,7 +426,7 @@ static void rcu_flavor_sched_clock_irq(int user);
>   static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
>   static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
>   static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
> -static bool rcu_is_callbacks_kthread(void);
> +static bool rcu_is_callbacks_kthread(struct rcu_data *rdp);
>   static void rcu_cpu_kthread_setup(unsigned int cpu);
>   static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp);
>   static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index c8ba0fe17267c..0483e1338c413 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1012,6 +1012,25 @@ static void rcu_cpu_kthread_setup(unsigned int cpu)
>   	WRITE_ONCE(rdp->rcuc_activity, jiffies);
>   }
>   
> +static bool rcu_is_callbacks_nocb_kthread(struct rcu_data *rdp)
> +{
> +#ifdef CONFIG_RCU_NOCB_CPU
> +	return rdp->nocb_cb_kthread == current;
> +#else
> +	return false;
> +#endif
> +}
> +
> +/*
> + * Is the current CPU running the RCU-callbacks kthread?
> + * Caller must have preemption disabled.
> + */
> +static bool rcu_is_callbacks_kthread(struct rcu_data *rdp)
> +{
> +	return rdp->rcu_cpu_kthread_task == current ||
> +			rcu_is_callbacks_nocb_kthread(rdp);
> +}
> +
>   #ifdef CONFIG_RCU_BOOST
>   
>   /*
> @@ -1151,15 +1170,6 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
>   	}
>   }
>   
> -/*
> - * Is the current CPU running the RCU-callbacks kthread?
> - * Caller must have preemption disabled.
> - */
> -static bool rcu_is_callbacks_kthread(void)
> -{
> -	return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current;
> -}
> -
>   #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
>   
>   /*
> @@ -1242,11 +1252,6 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
>   	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
>   }
>   
> -static bool rcu_is_callbacks_kthread(void)
> -{
> -	return false;
> -}
> -
>   static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
>   {
>   }