linux-kernel - Re: [PATCH] rcu/nocb: Fix dump_tree hierarchy print always active

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Date:   Mon, 07 Oct 2019 17:56:33 +0000
From:   Stefan <stefan@...aker.at>
To:     paulmck@...nel.org
Cc:     rcu@...r.kernel.org, Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu/nocb: Fix dump_tree hierarchy print always active

On 07/10/2019 03:26, Paul E. McKenney wrote:
> 
> On Fri, Oct 04, 2019 at 03:24:02PM -0700, Paul E. McKenney wrote:
>> On Fri, Oct 04, 2019 at 07:49:10PM +0000, Stefan Reiter wrote:
>>> Commit 18cd8c93e69e ("rcu/nocb: Print gp/cb kthread hierarchy if
>>> dump_tree") added print statements to rcu_organize_nocb_kthreads for
>>> debugging, but incorrectly guarded them, causing the function to always
>>> spew out its message.
>>>
>>> This patch fixes it by guarding both pr_alert statements with dump_tree,
>>> while also changing the second pr_alert to a pr_cont, to print the
>>> hierarchy in a single line (assuming that's how it was supposed to
>>> work).
>>>
>>> Fixes: 18cd8c93e69e ("rcu/nocb: Print gp/cb kthread hierarchy if dump_tree")
>>> Signed-off-by: Stefan Reiter <stefan@...aker.at>
>>
>> Queued for testing and review, thank you!
> 
> And here is an updated version to make the special case of a nocb GP
> kthread having no other nocb CB kthreads look less strange.  Does this
> work for you?

Tested just now, works for me. Thanks for the additional fix!

> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit e6223b0705369750990c32ddc80251942e61be30
> Author: Stefan Reiter <stefan@...aker.at>
> Date:   Fri Oct 4 19:49:10 2019 +0000
> 
>      rcu/nocb: Fix dump_tree hierarchy print always active
> 
>      Commit 18cd8c93e69e ("rcu/nocb: Print gp/cb kthread hierarchy if
>      dump_tree") added print statements to rcu_organize_nocb_kthreads for
>      debugging, but incorrectly guarded them, causing the function to always
>      spew out its message.
> 
>      This patch fixes it by guarding both pr_alert statements with dump_tree,
>      while also changing the second pr_alert to a pr_cont, to print the
>      hierarchy in a single line (assuming that's how it was supposed to
>      work).
> 
>      Fixes: 18cd8c93e69e ("rcu/nocb: Print gp/cb kthread hierarchy if dump_tree")
>      Signed-off-by: Stefan Reiter <stefan@...aker.at>
>      [ paulmck: Make single-nocbs-CPU GP kthreads look less erroneous. ]
>      Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index d5334e4..d43f4e0 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2295,6 +2295,8 @@ static void __init rcu_organize_nocb_kthreads(void)
>   {
>   	int cpu;
>   	bool firsttime = true;
> +	bool gotnocbs = false;
> +	bool gotnocbscbs = true;
>   	int ls = rcu_nocb_gp_stride;
>   	int nl = 0;  /* Next GP kthread. */
>   	struct rcu_data *rdp;
> @@ -2317,21 +2319,31 @@ static void __init rcu_organize_nocb_kthreads(void)
>   		rdp = per_cpu_ptr(&rcu_data, cpu);
>   		if (rdp->cpu >= nl) {
>   			/* New GP kthread, set up for CBs & next GP. */
> +			gotnocbs = true;
>   			nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
>   			rdp->nocb_gp_rdp = rdp;
>   			rdp_gp = rdp;
> -			if (!firsttime && dump_tree)
> -				pr_cont("\n");
> -			firsttime = false;
> -			pr_alert("%s: No-CB GP kthread CPU %d:", __func__, cpu);
> +			if (dump_tree) {
> +				if (!firsttime)
> +					pr_cont("%s\n", gotnocbscbs
> +							? "" : " (self only)");
> +				gotnocbscbs = false;
> +				firsttime = false;
> +				pr_alert("%s: No-CB GP kthread CPU %d:",
> +					 __func__, cpu);
> +			}
>   		} else {
>   			/* Another CB kthread, link to previous GP kthread. */
> +			gotnocbscbs = true;
>   			rdp->nocb_gp_rdp = rdp_gp;
>   			rdp_prev->nocb_next_cb_rdp = rdp;
> -			pr_alert(" %d", cpu);
> +			if (dump_tree)
> +				pr_cont(" %d", cpu);
>   		}
>   		rdp_prev = rdp;
>   	}
> +	if (gotnocbs && dump_tree)
> +		pr_cont("%s\n", gotnocbscbs ? "" : " (self only)");
>   }
> 
>   /*
>