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Date: Wed, 10 Aug 2016 11:29:05 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <waiman.long@hpe.com>
Cc: Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Will Deacon <Will.Deacon@arm.com>,
        Tim Chen <tim.c.chen@linux.intel.com>, Imre Deak <imre.deak@intel.com>
Subject: Re: [PATCH v4 3/3] locking/mutex: Ensure forward progress of
 waiter-spinner
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On Tue, Aug 09, 2016 at 02:00:00PM -0400, Waiman Long wrote:
> >Alternative might be to use the LSB of mutex::owner, but that's going to
> >be somewhat icky too.
> 
> I was thinking about doing that. However, the owner field is used in quite a
> number of places. It may be a bit risky to change all of them.

Agreed.

> >I'm not sure the 32bit platforms are going to be excited about growing
> >struct mutex...
> 
> Or we can make this a 64-bit architecture specific change if the increase in
> mutex size is a real concern. Actually, we don't need to use a list_head
> structure for wait_list. It can be just a pointer to mutex_waiter that has
> the list_head structure. This can save a pointer from the structure.

Just grow the thing, we can poke at it later if we get complaints.