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Re: [PATCH RFC 03/26] sched: Replace spin_unlock_wait() with lock/unlock pair

From Arnd Bergmann <arnd@arndb.de>
Newsgroups linux.kernel
Subject Re: [PATCH RFC 03/26] sched: Replace spin_unlock_wait() with lock/unlock pair
Date 2017-06-30 12:40 +0200
Message-ID <tY1vb-4jV-19@gated-at.bofh.it> (permalink)
References <tXRvP-663-1@gated-at.bofh.it> <tXRPb-6s4-9@gated-at.bofh.it>
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On Fri, Jun 30, 2017 at 2:01 AM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
> There is no agreed-upon definition of spin_unlock_wait()'s semantics,
> and it appears that all callers could do just as well with a lock/unlock
> pair.  This commit therefore replaces the spin_unlock_wait() call in
> do_task_dead() with spin_lock() followed immediately by spin_unlock().
> This should be safe from a performance perspective because the lock is
> this tasks ->pi_lock, and this is called only after the task exits.
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index e91138fcde86..6dea3d9728c8 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3461,7 +3461,8 @@ void __noreturn do_task_dead(void)
>          * is held by try_to_wake_up()
>          */
>         smp_mb();
> -       raw_spin_unlock_wait(&current->pi_lock);
> +       raw_spin_lock(&current->pi_lock);
> +       raw_spin_unlock(&current->pi_lock);

Does the raw_spin_lock()/raw_spin_unlock() imply an smp_mb() or stronger?
Maybe it would be clearer to remove the extra barrier if so.

     Arnd

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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
  [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
  [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

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