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Date:   Mon, 24 Jul 2023 13:50:48 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     thunder.leizhen@huaweicloud.com
Cc:     Frederic Weisbecker <frederic@kernel.org>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Zqiang <qiang.zhang1211@gmail.com>, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org, Zhen Lei <thunder.leizhen@huawei.com>
Subject: Re: [PATCH v2 1/1] rcu: Simplify check_cpu_stall()
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Reply-To: paulmck@kernel.org
References: <20230724022651.899-1-thunder.leizhen@huaweicloud.com>
 <20230724022651.899-2-thunder.leizhen@huaweicloud.com>
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On Mon, Jul 24, 2023 at 10:26:51AM +0800, thunder.leizhen@huaweicloud.com wrote:
> From: Zhen Lei <thunder.leizhen@huawei.com>
> 
> The code and comments of self detected and other detected are the same
> except the output function. Combine the same parts to avoid duplication.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>

Queued and pushed, thank you!!!

							Thanx, Paul

> ---
>  kernel/rcu/tree_stall.h | 42 +++++++++++++++--------------------------
>  1 file changed, 15 insertions(+), 27 deletions(-)
> 
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index cc884cd49e026a3..b45d7e49944cdd7 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -711,7 +711,7 @@ static void print_cpu_stall(unsigned long gps)
>  
>  static void check_cpu_stall(struct rcu_data *rdp)
>  {
> -	bool didstall = false;
> +	bool self_detected;
>  	unsigned long gs1;
>  	unsigned long gs2;
>  	unsigned long gps;
> @@ -758,10 +758,10 @@ static void check_cpu_stall(struct rcu_data *rdp)
>  		return; /* No stall or GP completed since entering function. */
>  	rnp = rdp->mynode;
>  	jn = jiffies + ULONG_MAX / 2;
> +	self_detected = READ_ONCE(rnp->qsmask) & rdp->grpmask;
>  	if (rcu_gp_in_progress() &&
> -	    (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
> +	    (self_detected || ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) &&
>  	    cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
> -
>  		/*
>  		 * If a virtual machine is stopped by the host it can look to
>  		 * the watchdog like an RCU stall. Check to see if the host
> @@ -770,33 +770,21 @@ static void check_cpu_stall(struct rcu_data *rdp)
>  		if (kvm_check_and_clear_guest_paused())
>  			return;
>  
> -		/* We haven't checked in, so go dump stack. */
> -		print_cpu_stall(gps);
> -		if (READ_ONCE(rcu_cpu_stall_ftrace_dump))
> -			rcu_ftrace_dump(DUMP_ALL);
> -		didstall = true;
> -
> -	} else if (rcu_gp_in_progress() &&
> -		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
> -		   cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
> -
> -		/*
> -		 * If a virtual machine is stopped by the host it can look to
> -		 * the watchdog like an RCU stall. Check to see if the host
> -		 * stopped the vm.
> -		 */
> -		if (kvm_check_and_clear_guest_paused())
> -			return;
> +		if (self_detected) {
> +			/* We haven't checked in, so go dump stack. */
> +			print_cpu_stall(gps);
> +		} else {
> +			/* They had a few time units to dump stack, so complain. */
> +			print_other_cpu_stall(gs2, gps);
> +		}
>  
> -		/* They had a few time units to dump stack, so complain. */
> -		print_other_cpu_stall(gs2, gps);
>  		if (READ_ONCE(rcu_cpu_stall_ftrace_dump))
>  			rcu_ftrace_dump(DUMP_ALL);
> -		didstall = true;
> -	}
> -	if (didstall && READ_ONCE(rcu_state.jiffies_stall) == jn) {
> -		jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
> -		WRITE_ONCE(rcu_state.jiffies_stall, jn);
> +
> +		if (READ_ONCE(rcu_state.jiffies_stall) == jn) {
> +			jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
> +			WRITE_ONCE(rcu_state.jiffies_stall, jn);
> +		}
>  	}
>  }
>  
> -- 
> 2.25.1
>