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Date: Wed, 10 Sep 2014 15:08:32 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Peter Hurley <peter@hurleysoftware.com>
Cc: Ingo Molnar <mingo@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.cz>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 13/26] locking: Add non-fatal spin lock assert
Message-ID: <20140910130832.GY4783@worktop.ger.corp.intel.com>
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On Wed, Sep 10, 2014 at 07:02:10AM -0400, Peter Hurley wrote:
> On 09/04/2014 01:14 AM, Ingo Molnar wrote:
> > 
> > * Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> >> On Wed, Sep 03, 2014 at 10:50:01AM -0400, Peter Hurley wrote:
> >>> So a lockdep-only assert is unlikely to draw attention to existing bugs,
> >>> especially in established drivers.
> >>
> >> By the same logic lockdep will not find locking errors in established
> >> drivers.
> > 
> > Indeed, this patch is ill-advised in several ways:
> > 
> >   - it extends an API variant that we want to phase
> > 
> >   - emits a warning even if say lockdep has already emitted a
> >     warning and locking state is not guaranteed to be consistent. 
> > 
> >   - makes the kernel more expensive once fully debugged, in that
> >     non-fatal checks are unconditional.
> 
> Ok.
> 
> One thing: I'm not seeing how lockdep_assert_held() switches off once
> the warning has been emitted? Is the caller expected to construct their
> own _ONCE tags?

Indeed, it does not do that. I suppose you can add
lockdep_assert_held_once() or somesuch if you think the once thing is
important.