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Message-ID: <54102FB2.1020808@hurleysoftware.com>
Date: Wed, 10 Sep 2014 07:02:10 -0400
From: Peter Hurley <peter@hurleysoftware.com>
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To: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>
CC: 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
References: <1409693975-1028-1-git-send-email-peter@hurleysoftware.com> <1409693975-1028-14-git-send-email-peter@hurleysoftware.com> <20140903092723.GA4783@worktop.ger.corp.intel.com> <5406F964.6060900@hurleysoftware.com> <20140903144029.GA7083@twins.programming.kicks-ass.net> <54072A99.1080306@hurleysoftware.com> <20140903150729.GA7436@twins.programming.kicks-ass.net> <20140904051411.GA27350@gmail.com>
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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?

Regards,
Peter Hurley