linux-kernel - Re: lockdep null-ptr-deref

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Message-ID: <20201002133536.GF17810@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net>
Date:   Fri, 2 Oct 2020 21:35:36 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     g@...ez.programming.kicks-ass.net, Qian Cai <cai@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: lockdep null-ptr-deref

On Fri, Oct 02, 2020 at 03:09:29PM +0200, Peter Zijlstra wrote:
> On Fri, Oct 02, 2020 at 08:36:02PM +0800, Boqun Feng wrote:
> 
> > But what if f2() is called with interrupt disabled? Or f2() disables
> > interrupt inside the function, like:
> > 
> > 	void f2(...)
> > 	{
> > 		local_irq_disable();
> > 		spin_lock(&B);
> > 		g(...);
> > 		...
> > 		local_irq_enable();
> > 	}
> > 
> > In this case, there wouldn't be any LOCK_ENABLED_*_READ usage for
> > rwlock_t A. As a result, we won't see it in the lockdep splat.
> 
> Hurm, fair enough. So just to make sure, you're arguing for:
> 
> -#define LOCK_TRACE_STATES              (XXX_LOCK_USAGE_STATES*4 + 1)
> +#define LOCK_TRACE_STATES              (XXX_LOCK_USAGE_STATES*4 + 2)
> 
> On top of my earlier patch, right?

Yep. Thanks ;-)

Regards,
Boqun