linux-kernel - Re: [PATCH v2 tip/core/rcu 02/18] lockdep: Make RCU suspicious-access splats use pr

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Message-ID: <20170121204023.im7ysfl2jdix5jox@x>
Date:   Sat, 21 Jan 2017 12:40:23 -0800
From:   Josh Triplett <josh@...htriplett.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
        fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH v2 tip/core/rcu 02/18] lockdep: Make RCU
 suspicious-access splats use pr_err

On Tue, Jan 17, 2017 at 06:53:41PM -0800, Paul E. McKenney wrote:
> This commit switches RCU suspicious-access splats use pr_err()
> instead of the current INFO printk()s.  This change makes it easier
> to automatically classify splats.
> 
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  kernel/locking/lockdep.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 7c38f8f3d97b..a74c0630172a 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -4412,13 +4412,13 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
>  #endif /* #ifdef CONFIG_PROVE_RCU_REPEATEDLY */
>  	/* Note: the following can be executed concurrently, so be careful. */
>  	printk("\n");
> -	printk("===============================\n");
> -	printk("[ INFO: suspicious RCU usage. ]\n");
> +	pr_err("===============================\n");
> +	pr_err("[  suspicious RCU usage.      ]\n");

While re-adding the square bracket makes it symmetric, this change still
seems odd, and unrelated to the switch to pr_err.  You could change it
to "ERR:" if you want, if "INFO:" feels inaccurate to you.

>  	print_kernel_ident();
> -	printk("-------------------------------\n");
> -	printk("%s:%d %s!\n", file, line, s);
> -	printk("\nother info that might help us debug this:\n\n");
> -	printk("\n%srcu_scheduler_active = %d, debug_locks = %d\n",
> +	pr_err("-------------------------------\n");
> +	pr_err("%s:%d %s!\n", file, line, s);
> +	pr_err("\nother info that might help us debug this:\n\n");
> +	pr_err("\n%srcu_scheduler_active = %d, debug_locks = %d\n",
>  	       !rcu_lockdep_current_cpu_online()
>  			? "RCU used illegally from offline CPU!\n"
>  			: !rcu_is_watching()
> -- 
> 2.5.2
>