linux-kernel - Re: [PATCH v2 2/2] debugobjects: Disable lockdep tracking of debugobjects internal locks

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Message-ID: <20180925153241.GD29985@hirez.programming.kicks-ass.net>
Date:   Tue, 25 Sep 2018 17:32:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Arnd Bergmann <arnd@...db.de>, chuhu@...hat.com
Subject: Re: [PATCH v2 2/2] debugobjects: Disable lockdep tracking of
 debugobjects internal locks

On Tue, Sep 25, 2018 at 10:41:09AM -0400, Waiman Long wrote:
> diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> index 70935ed91125..68d72ed9ca22 100644
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -1106,8 +1106,15 @@ void __init debug_objects_early_init(void)
>  {
>  	int i;
>  
> -	for (i = 0; i < ODEBUG_HASH_SIZE; i++)
> +	/*
> +	 * We don't need lockdep to verify correctness of debugobjects
> +	 * internal locks.
> +	 */
> +	lockdep_set_novalidate_class(&pool_lock);
> +	for (i = 0; i < ODEBUG_HASH_SIZE; i++) {
>  		raw_spin_lock_init(&obj_hash[i].lock);
> +		lockdep_set_novalidate_class(&obj_hash[i].lock);
> +	}
>  
>  	for (i = 0; i < ODEBUG_POOL_SIZE; i++)
>  		hlist_add_head(&obj_static_pool[i].node, &obj_pool);

NAK, we do not _EVER_ set novalidate if it can at all be avoided.

If there is a severe performance problem with lockdep, try and cure
that. But really, who runs lockdep kernels on 8 sockets?