netdev - Re: [PATCH v2 0/9] Remove spin_unlock

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Date:   Fri, 7 Jul 2017 10:06:21 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     David Laight <David.Laight@...LAB.COM>,
        "'paulmck@...ux.vnet.ibm.com'" <paulmck@...ux.vnet.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "oleg@...hat.com" <oleg@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dave@...olabs.net" <dave@...olabs.net>,
        "manfred@...orfullife.com" <manfred@...orfullife.com>,
        "tj@...nel.org" <tj@...nel.org>, "arnd@...db.de" <arnd@...db.de>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "will.deacon@....com" <will.deacon@....com>,
        "stern@...land.harvard.edu" <stern@...land.harvard.edu>,
        "parri.andrea@...il.com" <parri.andrea@...il.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 0/9] Remove spin_unlock_wait()


* Peter Zijlstra <peterz@...radead.org> wrote:

> > It might even be that this is the defined semantics of spin_unlock_wait().
> 
> As is, spin_unlock_wait() is somewhat ill defined. IIRC it grew from an 
> optimization by Oleg and subsequently got used elsewhere. And it being the 
> subtle bugger it is, there were bugs.

I believe the historical, original spin_unlock_wait() came from early SMP 
optimizations of the networking code - and then spread elsewhere, step by step. 
All but one of the networking uses went away since then - so I don't think there's 
any original usecase left.

Thanks,

	Ingo