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Re: [RFC] arm64: Enforce observed order for spinlock and data

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On Fri, Sep 30, 2016 at 01:40:57PM -0400, Brent DeGraaf wrote:
> Prior spinlock code solely used load-acquire and store-release
> semantics to ensure ordering of the spinlock lock and the area it
> protects. However, store-release semantics and ordinary stores do
> not protect against accesses to the protected area being observed
> prior to the access that locks the lock itself.
> 
> While the load-acquire and store-release ordering is sufficient
> when the spinlock routines themselves are strictly used, other
> kernel code that references the lock values directly (e.g. lockrefs)

Isn't the problem with lockref the fact that arch_spin_value_unlocked()
isn't a load-acquire, and therefore the CPU in question doesn't need to
observe the contents of the critical section etc..?

That is, wouldn't fixing arch_spin_value_unlocked() by making that an
smp_load_acquire() fix things much better?

> could observe changes to the area protected by the spinlock prior
> to observance of the lock itself being in a locked state, despite
> the fact that the spinlock logic itself is correct.

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[RFC] arm64: Enforce observed order for spinlock and data Brent DeGraaf <bdegraaf@codeaurora.org> - 2016-09-30 19:50 +0200
  Re: [RFC] arm64: Enforce observed order for spinlock and data Robin Murphy <robin.murphy@arm.com> - 2016-09-30 20:50 +0200
    Re: [RFC] arm64: Enforce observed order for spinlock and data bdegraaf@codeaurora.org - 2016-10-01 17:50 +0200
  Re: [RFC] arm64: Enforce observed order for spinlock and data Peter Zijlstra <peterz@infradead.org> - 2016-09-30 21:00 +0200
  Re: [RFC] arm64: Enforce observed order for spinlock and data Peter Zijlstra <peterz@infradead.org> - 2016-09-30 21:10 +0200
    Re: [RFC] arm64: Enforce observed order for spinlock and data bdegraaf@codeaurora.org - 2016-10-01 18:10 +0200
  Re: [RFC] arm64: Enforce observed order for spinlock and data Mark Rutland <mark.rutland@arm.com> - 2016-09-30 21:40 +0200
    Re: [RFC] arm64: Enforce observed order for spinlock and data bdegraaf@codeaurora.org - 2016-10-01 18:20 +0200
      Re: [RFC] arm64: Enforce observed order for spinlock and data Mark Rutland <mark.rutland@arm.com> - 2016-10-01 20:20 +0200
        Re: [RFC] arm64: Enforce observed order for spinlock and data bdegraaf@codeaurora.org - 2016-10-03 21:30 +0200
          Re: [RFC] arm64: Enforce observed order for spinlock and data Peter Zijlstra <peterz@infradead.org> - 2016-10-04 09:00 +0200
          Re: [RFC] arm64: Enforce observed order for spinlock and data Mark Rutland <mark.rutland@arm.com> - 2016-10-04 12:20 +0200
            Re: [RFC] arm64: Enforce observed order for spinlock and data bdegraaf@codeaurora.org - 2016-10-04 20:00 +0200
              Re: [RFC] arm64: Enforce observed order for spinlock and data bdegraaf@codeaurora.org - 2016-10-04 20:30 +0200
              Re: [RFC] arm64: Enforce observed order for spinlock and data Mark Rutland <mark.rutland@arm.com> - 2016-10-04 21:20 +0200
                Re: [RFC] arm64: Enforce observed order for spinlock and data bdegraaf@codeaurora.org - 2016-10-05 17:00 +0200
                Re: [RFC] arm64: Enforce observed order for spinlock and data bdegraaf@codeaurora.org - 2016-10-05 17:20 +0200
                Re: [RFC] arm64: Enforce observed order for spinlock and data Peter Zijlstra <peterz@infradead.org> - 2016-10-05 17:20 +0200
                Re: [RFC] arm64: Enforce observed order for spinlock and data bdegraaf@codeaurora.org - 2016-10-05 17:40 +0200
                Re: [RFC] arm64: Enforce observed order for spinlock and data bdegraaf@codeaurora.org - 2016-10-12 22:10 +0200

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