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Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock()

From Benjamin Herrenschmidt <benh@kernel.crashing.org>
Newsgroups linux.kernel
Subject Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock()
Date 2015-07-18 00:20 +0200
Message-ID <pNm94-1IO-9@gated-at.bofh.it> (permalink)
References (5 earlier) <pMJAJ-5aZ-1@gated-at.bofh.it> <pMJKq-5my-9@gated-at.bofh.it> <pMT73-22W-15@gated-at.bofh.it> <pN0ie-3Os-21@gated-at.bofh.it> <pNahz-1uy-13@gated-at.bofh.it>
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On Fri, 2015-07-17 at 10:32 +0100, Will Deacon wrote:
>  static inline void arch_spin_unlock(arch_spinlock_t *lock)
>  {
> -       SYNC_IO;
> -       __asm__ __volatile__("# arch_spin_unlock\n\t"
> -                               PPC_RELEASE_BARRIER: : :"memory");
> +       smp_mb();
>         lock->slock = 0;
>  }

That probably needs to be mb() in case somebody has the expectation that
it does a barrier vs. DMA on UP.

Cheers,
Ben.


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Thread

[RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-13 14:20 +0200
  Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Peter Zijlstra <peterz@infradead.org> - 2015-07-14 10:40 +0200
  Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-14 12:10 +0200
    Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-14 21:40 +0200
      Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-15 03:40 +0200
        Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-15 13:00 +0200
          Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-15 15:20 +0200
  Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Michael Ellerman <mpe@ellerman.id.au> - 2015-07-15 05:10 +0200
    Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-15 12:50 +0200
      Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Michael Ellerman <mpe@ellerman.id.au> - 2015-07-16 04:10 +0200
        Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-16 17:20 +0200
          Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2015-07-17 01:00 +0200
            Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-17 11:40 +0200
              Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Peter Zijlstra <peterz@infradead.org> - 2015-07-17 12:20 +0200
                Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-17 14:50 +0200
              Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2015-07-18 00:20 +0200
                Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-20 15:40 +0200
                Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-20 15:50 +0200
                Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-20 16:00 +0200
    Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-15 16:20 +0200
      Re: [RFC PATCH v2] memory-barriers: remove  smp_mb__after_unlock_lock() Michael Ellerman <mpe@ellerman.id.au> - 2015-07-16 03:40 +0200

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