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Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic definitions

From Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups linux.kernel
Subject Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic definitions
Date 2017-07-03 18:50 +0200
Message-ID <tZcHT-43W-11@gated-at.bofh.it> (permalink)
References (3 earlier) <tY3x0-5xi-25@gated-at.bofh.it> <tY402-5YH-21@gated-at.bofh.it> <tYcqB-2Lm-5@gated-at.bofh.it> <tZ9qF-1XI-9@gated-at.bofh.it> <tZceT-3TE-43@gated-at.bofh.it>
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On Mon, Jul 3, 2017 at 9:18 AM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
>
> Agreed, and my next step is to look at spin_lock() followed by
> spin_is_locked(), not necessarily the same lock.

Hmm. Most (all?) "spin_is_locked()" really should be about the same
thread that took the lock (ie it's about asserts and lock debugging).

The optimistic ABBA avoidance pattern for spinlocks *should* be

    spin_lock(inner)
    ...
    if (!try_lock(outer)) {
           spin_unlock(inner);
           .. do them in the right order ..

so I don't think spin_is_locked() should have any memory barriers.

In fact, the core function for spin_is_locked() is arguably
arch_spin_value_unlocked() which doesn't even do the access itself.

                       Linus

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[PATCH RFC 0/26] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:00 +0200
  [PATCH RFC 13/26] blackfin: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
    Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions Will Deacon <will.deacon@arm.com> - 2017-06-30 11:20 +0200
      Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 14:50 +0200
        Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions Will Deacon <will.deacon@arm.com> - 2017-06-30 15:20 +0200
          Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-01 00:20 +0200
            Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions Will Deacon <will.deacon@arm.com> - 2017-07-03 15:20 +0200
              Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-03 18:20 +0200
                Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic definitions Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-03 18:50 +0200
                Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions Will Deacon <will.deacon@arm.com> - 2017-07-03 19:20 +0200
                Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-04 00:40 +0200
                Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic definitions Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-04 01:00 +0200
                Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-04 02:50 +0200
                Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-04 03:00 +0200
                Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-03 23:20 +0200
  [PATCH RFC 23/26] sh: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 16/26] m32r: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 21/26] powerpc: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
    Re: [PATCH RFC 21/26] powerpc: Remove spin_unlock_wait()  arch-specific definitions Boqun Feng <boqun.feng@gmail.com> - 2017-07-02 06:00 +0200
      Re: [PATCH RFC 21/26] powerpc: Remove spin_unlock_wait()  arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-06 02:00 +0200
  [PATCH RFC 25/26] tile: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
    Re: [PATCH RFC 25/26] tile: Remove spin_unlock_wait() arch-specific definitions Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-30 02:10 +0200
      Re: [PATCH RFC 25/26] tile: Remove spin_unlock_wait() arch-specific definitions Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-30 02:20 +0200
        Re: [PATCH RFC 25/26] tile: Remove spin_unlock_wait() arch-specific  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:30 +0200
      Re: [PATCH RFC 25/26] tile: Remove spin_unlock_wait() arch-specific  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:20 +0200
      Re: [PATCH RFC 25/26] tile: Remove spin_unlock_wait() arch-specific  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:20 +0200
  [PATCH RFC 18/26] mips: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 19/26] mn10300: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 20/26] parisc: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 15/26] ia64: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 11/26] arm: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 22/26] s390: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 01/26] netfilter: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
    Re: [PATCH RFC 01/26] netfilter: Replace spin_unlock_wait() with  lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-02 04:10 +0200
  [PATCH RFC 04/26] completion: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 07/26] drivers/ata: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 14/26] hexagon: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 09/26] alpha: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 24/26] sparc: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 26/26] xtensa: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:10 +0200
  [PATCH RFC 03/26] sched: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:20 +0200
    Re: [PATCH RFC 03/26] sched: Replace spin_unlock_wait() with  lock/unlock pair Arnd Bergmann <arnd@arndb.de> - 2017-06-30 12:40 +0200
      Re: [PATCH RFC 03/26] sched: Replace spin_unlock_wait() with  lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 14:40 +0200
  [PATCH RFC 05/26] exit: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:20 +0200
  [PATCH RFC 12/26] arm64: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:20 +0200
    Re: [PATCH RFC 12/26] arm64: Remove spin_unlock_wait() arch-specific  definitions Will Deacon <will.deacon@arm.com> - 2017-06-30 11:30 +0200
      Re: [PATCH RFC 12/26] arm64: Remove spin_unlock_wait() arch-specific  definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 19:40 +0200
  [PATCH RFC 10/26] arc: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:20 +0200
  [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 02:20 +0200
    Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with  lock/unlock pair Oleg Nesterov <oleg@redhat.com> - 2017-06-30 13:10 +0200
      Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with  lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 15:00 +0200
        Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with  lock/unlock pair Oleg Nesterov <oleg@redhat.com> - 2017-06-30 17:30 +0200
          Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with  lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 18:20 +0200
            Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with  lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 19:30 +0200
            Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with  lock/unlock pair Oleg Nesterov <oleg@redhat.com> - 2017-06-30 21:30 +0200
              Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with  lock/unlock pair Alan Stern <stern@rowland.harvard.edu> - 2017-06-30 22:00 +0200
                Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with  lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 22:10 +0200
              Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with  lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 22:10 +0200
                Re: [PATCH RFC 02/26] task_work: Replace spin_unlock_wait() with  lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-06-30 22:20 +0200
  Re: [PATCH RFC 06/26] ipc: Replace spin_unlock_wait() with  lock/unlock pair Manfred Spraul <manfred@colorfullife.com> - 2017-07-01 21:30 +0200
    Re: [PATCH RFC 06/26] ipc: Replace spin_unlock_wait() with  lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-02 05:20 +0200
  [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-06 01:40 +0200
    [PATCH v2 9/9] arch: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-06 01:40 +0200
    RE: [PATCH v2 0/9] Remove spin_unlock_wait() David Laight <David.Laight@ACULAB.COM> - 2017-07-06 16:20 +0200
      Re: [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-06 17:30 +0200
        Re: [PATCH v2 0/9] Remove spin_unlock_wait() Peter Zijlstra <peterz@infradead.org> - 2017-07-06 18:20 +0200
          Re: [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-06 18:30 +0200
            Re: [PATCH v2 0/9] Remove spin_unlock_wait() Peter Zijlstra <peterz@infradead.org> - 2017-07-06 18:50 +0200
              Re: [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-06 19:10 +0200
            Re: [PATCH v2 0/9] Remove spin_unlock_wait() Alan Stern <stern@rowland.harvard.edu> - 2017-07-06 18:50 +0200
              Re: [PATCH v2 0/9] Remove spin_unlock_wait() Peter Zijlstra <peterz@infradead.org> - 2017-07-06 19:00 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() Alan Stern <stern@rowland.harvard.edu> - 2017-07-06 21:40 +0200
      Re: [PATCH v2 0/9] Remove spin_unlock_wait() Peter Zijlstra <peterz@infradead.org> - 2017-07-06 18:10 +0200
        Re: [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-06 18:30 +0200
          Re: [PATCH v2 0/9] Remove spin_unlock_wait() Peter Zijlstra <peterz@infradead.org> - 2017-07-06 19:00 +0200
            Re: [PATCH v2 0/9] Remove spin_unlock_wait() Will Deacon <will.deacon@arm.com> - 2017-07-06 19:10 +0200
              Re: [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-06 19:30 +0200
            Re: [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-06 19:20 +0200
            Re: [PATCH v2 0/9] Remove spin_unlock_wait() Ingo Molnar <mingo@kernel.org> - 2017-07-07 10:40 +0200
              Re: [PATCH v2 0/9] Remove spin_unlock_wait() Peter Zijlstra <peterz@infradead.org> - 2017-07-07 10:50 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() Ingo Molnar <mingo@kernel.org> - 2017-07-07 12:40 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() Peter Zijlstra <peterz@infradead.org> - 2017-07-07 13:30 +0200
              Re: [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-07 16:50 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() Ingo Molnar <mingo@kernel.org> - 2017-07-08 10:50 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-08 13:50 +0200
              Re: [PATCH v2 0/9] Remove spin_unlock_wait() Manfred Spraul <manfred@colorfullife.com> - 2017-07-07 19:50 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() Ingo Molnar <mingo@kernel.org> - 2017-07-08 10:40 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-08 13:50 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() Ingo Molnar <mingo@kernel.org> - 2017-07-08 14:40 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-08 16:50 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() Alan Stern <stern@rowland.harvard.edu> - 2017-07-08 18:30 +0200
                Re: [PATCH v2 0/9] Remove spin_unlock_wait() Manfred Spraul <manfred@colorfullife.com> - 2017-07-10 19:30 +0200
        Re: [PATCH v2 0/9] Remove spin_unlock_wait() Ingo Molnar <mingo@kernel.org> - 2017-07-07 10:10 +0200
          Re: [PATCH v2 0/9] Remove spin_unlock_wait() Ingo Molnar <mingo@kernel.org> - 2017-07-07 11:40 +0200
    [PATCH v3 0/9] Remove spin_unlock_wait() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-07 21:30 +0200
      [PATCH v3 9/9] arch: Remove spin_unlock_wait() arch-specific definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-07 21:40 +0200
      [PATCH v3 5/9] exit: Replace spin_unlock_wait() with lock/unlock pair "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-07 21:40 +0200
      [PATCH v3 8/9] locking: Remove spin_unlock_wait() generic definitions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-07 21:40 +0200

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