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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 3 Jul 2017 15:49:42 -0700
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Subject: Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic definitions
To: Paul McKenney <paulmck@linux.vnet.ibm.com>
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On Mon, Jul 3, 2017 at 3:30 PM, Paul E. McKenney
<paulmck@linux.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