linux-kernel - Re: [PATCH RFC 08/26] locking: Remove spin_unlock

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Date:   Mon, 3 Jul 2017 15:49:42 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:     Will Deacon <will.deacon@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        NetFilter <netfilter-devel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Manfred Spraul <manfred@...orfullife.com>,
        Tejun Heo <tj@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>
Subject: Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic definitions

On Mon, Jul 3, 2017 at 3:30 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
>
> That certainly is one interesting function, isn't it?  I wonder what
> happens if you replace the raw_spin_is_locked() calls with an
> unlock under a trylock check?  ;-)

Deadlock due to interrupts again?

Didn't your spin_unlock_wait() patches teach you anything? Checking
state is fundamentally different from taking the lock. Even a trylock.

I guess you could try with the irqsave versions. But no, we're not doing that.

                Linus