linux-kernel - Re: [PATCH] lockdep: Show up to three levels for a deadlock scenario

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Date:   Tue, 19 Dec 2017 11:54:10 -0500
From:   Dhaval Giani <dhaval.giani@...cle.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] lockdep: Show up to three levels for a deadlock scenario

On 2017-12-19 11:52 AM, Steven Rostedt wrote:
> On Tue, 19 Dec 2017 17:46:19 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> 
>> It really isn't that hard, Its mostly a question of TL;DR.
>>
>> #0 is useless and should be thrown out
>> #1 shows where we take #1 while holding #0
>> ..
>> #n shows where we take #n while holding #n-1
>>
>> And the bottom callstack shows where we take #0 while holding #n. Which
>> gets you a nice circle in your graph, which spells deadlock.
>>
>> Plenty people have shown they get this stuff.
> 
> 
> Then I suggest that you can either take my patch to improve the
> visual or remove the visual completely, as nobody cares about it.
> 

I prefer the former. As Steven has mentioned elsewhere, people find
lockdep output hard to follow (enough that he has given talks :) )

Dhaval