Re: spin_lock implicit/explicit memory barrier

From	Davidlohr Bueso <dave@stgolabs.net>
Newsgroups	linux.kernel
Subject	Re: spin_lock implicit/explicit memory barrier
Date	2016-08-11 20:40 +0200
Message-ID	<s533A-7sT-15@gated-at.bofh.it> (permalink)
References	(3 earlier) <s4ILv-1Hq-19@gated-at.bofh.it> <s4KaC-2JP-31@gated-at.bofh.it> <s4KDE-2TN-27@gated-at.bofh.it> <s4Lgl-3pe-1@gated-at.bofh.it> <s4Tnz-1hD-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Thu, 11 Aug 2016, Peter Zijlstra wrote:

>On Wed, Aug 10, 2016 at 04:29:22PM -0700, Davidlohr Bueso wrote:
>
>> (1) As Manfred suggested, have a patch 1 that fixes the race against mainline
>> with the redundant smp_rmb, then apply a second patch that gets rid of it
>> for mainline, but only backport the original patch 1 down to 3.12.
>
>I have not followed the thread closely, but this seems like the best
>option. Esp. since 726328d92a42 ("locking/spinlock, arch: Update and fix
>spin_unlock_wait() implementations") is incomplete, it relies on at
>least 6262db7c088b ("powerpc/spinlock: Fix spin_unlock_wait()") to sort
>PPC.

Yeah, and we'd also need the arm bits; which reminds me, aren't alpha
ldl_l/stl_c sequences also exposed to this delaying of the publishing
when a non-owner peeks at the lock? Right now sysv sem's would be busted
when doing either is_locked or unlock_wait, shouldn't these be pimped up
to full smp_mb()s?

Thanks,
Davidlohr

Thread

Re: spin_lock implicit/explicit memory barrier Davidlohr Bueso <dave@stgolabs.net> - 2016-08-11 00:30 +0200
  Re: spin_lock implicit/explicit memory barrier "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-11 01:00 +0200
    Re: spin_lock implicit/explicit memory barrier Davidlohr Bueso <dave@stgolabs.net> - 2016-08-11 01:40 +0200
      Re: spin_lock implicit/explicit memory barrier Peter Zijlstra <peterz@infradead.org> - 2016-08-11 10:20 +0200
        Re: spin_lock implicit/explicit memory barrier Davidlohr Bueso <dave@stgolabs.net> - 2016-08-11 20:40 +0200
          Re: spin_lock implicit/explicit memory barrier Boqun Feng <boqun.feng@gmail.com> - 2016-08-12 05:10 +0200
            Re: spin_lock implicit/explicit memory barrier Peter Zijlstra <peterz@infradead.org> - 2016-08-19 16:10 +0200
  Re: spin_lock implicit/explicit memory barrier Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-08-11 02:10 +0200

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