From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: [PATCHv2 5/6] xen: use ticket locks for spin locks
Date: Tue, 21 Apr 2015 10:59:11 +0100
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To: Tim Deegan <tim@xen.org>, David Vrabel <david.vrabel@citrix.com>
Cc: xen-devel@lists.xenproject.org, Keir Fraser <keir@xen.org>, Ian Campbell <ian.campbell@citrix.com>, Jan Beulich <jbeulich@suse.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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On 16/04/15 13:03, Tim Deegan wrote:
> 
>> +static int __spin_is_locked(spinlock_t *lock)
>> +{
>> +    return lock->tickets.head != lock->tickets.tail;
>> +}
> 
> Maybe atomic_read the lock and do the comparison on the local value?
> Just from an abundance of caution - can't think of an obvious reason
> why this race should matter.

I think it would be preferable to avoid giving the impression that
avoiding this race is important so I've left this as is (FWIW, the Linux
implementation is like this).

David