linux-kernel - Re: [PATCH 13/26] locking: Add non-fatal spin lock assert

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Message-ID: <54102FB2.1020808@hurleysoftware.com>
Date:	Wed, 10 Sep 2014 07:02:10 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 13/26] locking: Add non-fatal spin lock assert

On 09/04/2014 01:14 AM, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.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
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