Date: Mon, 9 Nov 2009 16:49:18 +0100
From: Jens Axboe <jens.axboe@oracle.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Tejun Heo <tj@kernel.org>, Jiri Kosina <jkosina@suse.cz>,
       Peter Zijlstra <peterz@infradead.org>,
       Yinghai Lu <yhlu.kernel@gmail.com>,
       Thomas Gleixner <tglx@linutronix.de>, cl@linux-foundation.org,
       linux-kernel@vger.kernel.org
Subject: Re: irq lock inversion
Message-ID: <20091109154918.GY8742@kernel.dk>
References: <4AF25FC7.4000502@kernel.org> <20091105082102.GA2870@elte.hu> <4AF28D7A.6020209@kernel.org> <alpine.LSU.2.00.0911051502060.9988@wotan.suse.de> <4AF3B9BD.9050300@kernel.org> <20091106071711.GA20946@elte.hu> <20091106095922.GH8742@kernel.dk> <20091108093859.GA2845@elte.hu> <20091109153418.GX8742@kernel.dk> <20091109154527.GA24969@elte.hu>
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On Mon, Nov 09 2009, Ingo Molnar wrote:
> 
> * Jens Axboe <jens.axboe@oracle.com> wrote:
> 
> > On Sun, Nov 08 2009, Ingo Molnar wrote:
> > > 
> > > * Jens Axboe <jens.axboe@oracle.com> wrote:
> > > 
> > > > On Fri, Nov 06 2009, Ingo Molnar wrote:
> > > > > Read the lockdep message please, consider all the backtraces it prints, 
> > > > > it says something different.
> > > > 
> > > > In all honesty, reading and parsing lockdep messages requires a 
> > > > special state of mind. IOW, readability is not its high point.
> > > 
> > > We frequently do patches to improve the messages but there's a hard 
> > > limit: generally the messages mirror the complexity of the underlying 
> > > locking scenario.
> > > 
> > > Unfortunately lockdep cannot pretend something is simple when it is not. 
> > > There are two ways out of that: either to simplify the underlying 
> > > locking rules, or to understand them.
> > 
> > I think the primary problem is that it tries to condense too much 
> > information, instead of just spelling it out. That may be obvious to a 
> > person intimately familiar with lockdep, but not to others. Things 
> > like the STATE line, for instance. It would read a lot easier if these 
> > things were just spelled out.
> > 
> > I know this message isn't really productive, just tossing it out 
> > there. I'll try to to back it up with a patch the next time it annoys 
> > me :-)
> 
> Well, previously lockdep spewed out a lot of info, which we condensed 
> down because people complained ;-)

Heh, can't win 'em all! Stack traces are so large anyway that I don't
think saving 1-2 lines per lock in the trace would make much of a
difference. It's debug output, after all.

-- 
Jens Axboe

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