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

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Date:   Fri, 4 Oct 2019 15:24:02 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Stefan Reiter <stefan@...aker.at>
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 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!

> ---
> 
> First time contributing to the kernel, hope I'm doing this right :)

Looks good so far.  Then again, I just kicked off the tests.  ;-)

							Thanx, Paul

>  kernel/rcu/tree_plugin.h | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 2defc7fe74c3..7cbf4a0f3eff 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2346,15 +2346,19 @@ static void __init rcu_organize_nocb_kthreads(void)
>  			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("\n");
> +				firsttime = false;
> +				pr_alert("%s: No-CB GP kthread CPU %d:",
> +					 __func__, cpu);
> +			}
>  		} else {
>  			/* Another CB kthread, link to previous GP kthread. */
>  			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;
>  	}
> -- 
> 2.23.0
> 
>