linux-kernel - Re: [PATCH] debugobjects: call debug_objects_mem

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Date:   Fri, 23 Nov 2018 22:46:33 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Waiman Long <longman@...hat.com>
cc:     Qian Cai <cai@....us>, akpm@...ux-foundation.org,
        yang.shi@...ux.alibaba.com, arnd@...db.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] debugobjects: call debug_objects_mem_init eariler

On Thu, 22 Nov 2018, Waiman Long wrote:
> On 11/22/2018 11:31 PM, Qian Cai wrote:
> > The current value of the early boot static pool size, 1024 is not big
> > enough for systems with large number of CPUs with timer or/and workqueue
> > objects selected. As the results, systems have 60+ CPUs with both timer
> > and workqueue objects enabled could trigger "ODEBUG: Out of memory.
> > ODEBUG disabled".
> >
> > However, none of the things are actually used or required beofre

before

> > debug_objects_mem_init() is invoked.
> >
> > According to tglx,
> > "the reason why the call is at this place in start_kernel() is
> > historical. It's because back in the days when debugobjects were added
> > the memory allocator was enabled way later than today. So we can just
> > move the debug_objects_mem_init() call right before sched_init()."
> >
> > Afterwards, when calling debug_objects_mem_init(), interrupts have
> > already been disabled and lockdep_init() will only be called later, so
> > no need to worry about interrupts in
> > debug_objects_replace_static_objects().

Just out of curiosity. How many objects are allocated between early and mem
init?

> > diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> > index 70935ed91125..cc5818ced652 100644
> > --- a/lib/debugobjects.c
> > +++ b/lib/debugobjects.c
> > @@ -1132,13 +1132,6 @@ static int __init debug_objects_replace_static_objects(void)
> >  		hlist_add_head(&obj->node, &objects);
> >  	}
> >  
> > -	/*
> > -	 * When debug_objects_mem_init() is called we know that only
> > -	 * one CPU is up, so disabling interrupts is enough
> > -	 * protection. This avoids the lockdep hell of lock ordering.
> > -	 */
> > -	local_irq_disable();
> 
> I think you should have a comment saying that debug_objects_mm_init() is
> called early with only one CPU up and interrupt disabled. So it is safe
> to replace static objects without any protection.

Yes please.
 
Thanks,

	tglx