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Re: [PATCH 4/4] locking: Introduce smp_cond_acquire()

From "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Newsgroups linux.kernel
Subject Re: [PATCH 4/4] locking: Introduce smp_cond_acquire()
Date 2015-11-12 16:50 +0100
Message-ID <qu2im-2in-23@gated-at.bofh.it> (permalink)
References (5 earlier) <qtID0-6tH-19@gated-at.bofh.it> <qtUkO-5Od-1@gated-at.bofh.it> <qu0JA-1tl-25@gated-at.bofh.it> <qu1mi-1Ij-11@gated-at.bofh.it> <qu1mi-1Ij-9@gated-at.bofh.it>
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On Thu, Nov 12, 2015 at 10:49:02PM +0800, Boqun Feng wrote:
> On Thu, Nov 12, 2015 at 06:40:04AM -0800, Paul E. McKenney wrote:
> [snip]
> > 
> > I cannot resist suggesting that any lock that interacts with
> > spin_unlock_wait() must have all relevant acquisitions followed by
> > smp_mb__after_unlock_lock().
> > 
> 
> But
> 
> 1.	This would expand the purpose of smp_mb__after_unlock_lock(),
> 	right? smp_mb__after_unlock_lock() is for making UNLOCK-LOCK
> 	pair global transitive rather than guaranteeing no operations
> 	can be reorder before the STORE part of LOCK/ACQUIRE.

Indeed it would.  Which might be OK.

> 2.	If ARM64 has the same problem as PPC now,
> 	smp_mb__after_unlock_lock() can't help, as it's a no-op on
> 	ARM64.

Agreed, and that is why we need Will to weigh in.

							Thanx, Paul

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Thread

[PATCH 0/4] scheduler ordering bits Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
  [PATCH 2/4] sched: Document Program-Order guarantees Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
    Re: [PATCH 2/4] sched: Document Program-Order guarantees Paul Turner <pjt@google.com> - 2015-11-02 21:30 +0100
      Re: [PATCH 2/4] sched: Document Program-Order guarantees Peter Zijlstra <peterz@infradead.org> - 2015-11-02 21:40 +0100
        Re: [PATCH 2/4] sched: Document Program-Order guarantees Paul Turner <pjt@google.com> - 2015-11-02 23:10 +0100
          Re: [PATCH 2/4] sched: Document Program-Order guarantees Peter Zijlstra <peterz@infradead.org> - 2015-11-02 23:20 +0100
  [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
    Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
      Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-02 18:50 +0100
        Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-03 02:20 +0100
          Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-03 02:30 +0100
    Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-02 18:50 +0100
    Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-02 19:10 +0100
      Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-02 19:40 +0100
        Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-02 20:20 +0100
          Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-02 21:00 +0100
            Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 21:30 +0100
          Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 23:00 +0100
          Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-03 03:00 +0100
            Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-03 20:50 +0100
              Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-04 05:00 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-04 05:50 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-04 14:10 +0100
      Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() David Howells <dhowells@redhat.com> - 2015-11-02 21:40 +0100
        Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 21:50 +0100
        Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-02 22:20 +0100
    Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-03 18:10 +0100
      Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-03 19:30 +0100
      Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Boqun Feng <boqun.feng@gmail.com> - 2015-11-11 10:50 +0100
        Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Boqun Feng <boqun.feng@gmail.com> - 2015-11-11 11:40 +0100
          Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-11 20:00 +0100
          Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 15:00 +0100
        Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-11 13:20 +0100
          Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-11 19:50 +0100
            Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-11 22:30 +0100
            Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Boqun Feng <boqun.feng@gmail.com> - 2015-11-12 08:20 +0100
              Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-12 11:30 +0100
              Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-12 15:10 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Boqun Feng <boqun.feng@gmail.com> - 2015-11-12 15:50 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 16:50 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-12 23:00 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 15:50 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-12 16:00 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 16:10 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-12 16:10 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 16:30 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-12 22:30 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Boqun Feng <boqun.feng@gmail.com> - 2015-11-12 16:20 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-12 18:50 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-12 19:10 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-12 19:40 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 20:00 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-12 22:40 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-13 00:50 +0100
              Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-12 19:30 +0100
                Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-12 23:10 +0100
  [PATCH 1/4] sched: Better document the try_to_wake_up() barriers Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
  [PATCH 3/4] sched: Fix a race in try_to_wake_up() vs schedule() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100

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