linux-kernel - Re: [PATCH 05/13] XFS: Fix lock ASSERT on UP

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Message-ID: <20120330140457.GH17822@one.firstfloor.org>
Date:	Fri, 30 Mar 2012 16:04:57 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>, xfs-masters@....sgi.com
Subject: Re: [PATCH 05/13] XFS: Fix lock ASSERT on UP

On Fri, Mar 30, 2012 at 03:13:48PM +1100, Dave Chinner wrote:
> On Fri, Mar 30, 2012 at 01:52:01AM +0200, Andi Kleen wrote:
> > On Thu, Mar 29, 2012 at 07:21:14PM -0400, Christoph Hellwig wrote:
> > > On Tue, Mar 27, 2012 at 05:47:09PM -0700, Andi Kleen wrote:
> > > > From: Andi Kleen <ak@...ux.intel.com>
> > > > 
> > > > ASSERT(!spin_is_locked()) doesn't work on UP builds. Replace with a standard
> > > > lockdep_assert_held()
> > > 
> > > The "standard" is assert_spin_locked() - which not only is much cheaper
> > > but also has the advantage of working in non-lockdep builds.
> > 
> > But then you have it unconditional, not just on debug builds.
> 
> And the problem with that is what? There is so little overhead to the
> check it doesn't matter that it is enabled in production kernels...

It's really interesting how much you guys argue for your buggy construct
which you clearly never tested on a UP build...

Not sure if that is a hot path, but on highly contended locks every cache line
fetch is quite expensive on larger systems.

also I doubt the thing really catches bugs, and if it did you would be 
probably better off with a sparse notation or so.

Anyways I will turn it into the normal assert.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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