linux-kernel - Re: + kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added to -mm tree

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Message-ID: <56B1CB7F.5070207@virtuozzo.com>
Date:	Wed, 3 Feb 2016 12:42:23 +0300
From:	Andrey Ryabinin <aryabinin@...tuozzo.com>
To:	Ingo Molnar <mingo@...nel.org>, <akpm@...ux-foundation.org>
CC:	<krinkin.m.u@...il.com>, <mingo@...e.hu>, <peterz@...radead.org>,
	<mm-commits@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: +
 kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added
 to -mm tree



On 02/03/2016 10:44 AM, Ingo Molnar wrote:

> Yuck, I don't really like this.
> 
> Lockdep initialization must happen early on, and it should happen in a well 
> defined place, not be opportunistic (and relatively random) like this, making it 
> dependent on config options and calling contexts.
> 
> Also, in addition to properly ordering UBSAN initialization, how about fixing the 
> silent crash by adding a lockdep warning to that place instead of an auto-init? 
> 
> The warning will turn lockdep off safely and will generate an actionable kernel 
> message and stackdump upon which the init ordering fix can be done.
> 

Something like this already done for DEBUG_LOCKDEP=y (except it initializes lockdep instead of turning it off).

look_up_lock_class():
...
	#ifdef CONFIG_DEBUG_LOCKDEP
		/*
		 * If the architecture calls into lockdep before initializing
		 * the hashes then we'll warn about it later. (we cannot printk
		 * right now)
		 */
		if (unlikely(!lockdep_initialized)) {
			lockdep_init();
			lockdep_init_error = 1;
			lock_init_error = lock->name;
			save_stack_trace(&lockdep_init_trace);
		}
	#endif


Silent crash happens only in DEBUG_LOCKDEP=n && LOCKDEP=y combination.
So, what about simply removing this #ifdef (and the other one in lockdep_info() )?
I