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

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Message-ID: <20201002130929.GW2628@hirez.programming.kicks-ass.net>
Date:   Fri, 2 Oct 2020 15:09:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Boqun Feng <boqun.feng@...il.com>
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 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?