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Re: [RFC][PATCH] Fix a race between rwsem and the scheduler

From Boqun Feng <boqun.feng@gmail.com>
Newsgroups linux.kernel
Subject Re: [RFC][PATCH] Fix a race between rwsem and the scheduler
Date 2016-09-01 16:20 +0200
Message-ID <scB0u-2VS-5@gated-at.bofh.it> (permalink)
References (5 earlier) <sbW6Z-8w9-9@gated-at.bofh.it> <sbYLv-1Qd-11@gated-at.bofh.it> <scdUe-2XV-15@gated-at.bofh.it> <sclyp-7Kc-23@gated-at.bofh.it> <scu8G-5sK-27@gated-at.bofh.it>
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On Thu, Sep 01, 2016 at 08:57:38AM +0200, Peter Zijlstra wrote:
> On Thu, Sep 01, 2016 at 07:47:10AM +1000, Benjamin Herrenschmidt wrote:
> 
> > > OK, for giggles, could you (or Balbir) check what happens if you take
> > > that sync out?
> 
> > The problem is no amount of testing can tell you it works for sure :-)
> 
> It breaking does prove the negative though, so still interesting.
> 
> > I would be nervous not having a real full sync in _switch. All we have
> > along the scheduler path is lwsync's and our isync based load construct
> > for spin_lock, I'm not sure what other assumptions we have around that
> > sync in there...
> 
> Only one way to find out  ;-)
> 
> I'm not saying you should commit that change, just curious if (and how
> fast) it would come apart.
> 
> At the very least we could update the comment that goes with that sync.

Could there be some code that relies on the full barrier semantics of
schedule() to provide transitivity?

IIUC, the Program Order Guarantee you stated before try_to_wake_up()
only has ordering effect on wakers and wakees.

Regards,
Boqun

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Thread

[RFC][PATCH] Fix a race between rwsem and the scheduler Balbir Singh <bsingharora@gmail.com> - 2016-08-30 10:50 +0200
  Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Nicholas Piggin <npiggin@gmail.com> - 2016-08-30 11:20 +0200
  Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Peter Zijlstra <peterz@infradead.org> - 2016-08-30 14:20 +0200
    Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Oleg Nesterov <oleg@redhat.com> - 2016-08-30 15:10 +0200
      Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Peter Zijlstra <peterz@infradead.org> - 2016-08-30 16:20 +0200
        Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Oleg Nesterov <oleg@redhat.com> - 2016-08-30 19:00 +0200
          Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Peter Zijlstra <peterz@infradead.org> - 2016-08-30 20:40 +0200
            Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-08-30 23:30 +0200
              Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Peter Zijlstra <peterz@infradead.org> - 2016-08-31 09:20 +0200
                Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-08-31 13:40 +0200
              Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Peter Zijlstra <peterz@infradead.org> - 2016-08-31 15:40 +0200
                Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-08-31 23:50 +0200
                Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Balbir Singh <bsingharora@gmail.com> - 2016-09-01 08:50 +0200
                Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Peter Zijlstra <peterz@infradead.org> - 2016-09-01 09:00 +0200
                Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Boqun Feng <boqun.feng@gmail.com> - 2016-09-01 16:20 +0200
                Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Peter Zijlstra <peterz@infradead.org> - 2016-09-01 17:40 +0200
      Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-08-30 23:30 +0200
        Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Peter Zijlstra <peterz@infradead.org> - 2016-08-31 09:30 +0200
          Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-08-31 13:40 +0200
    Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Balbir Singh <bsingharora@gmail.com> - 2016-08-31 05:50 +0200
      Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Peter Zijlstra <peterz@infradead.org> - 2016-08-31 09:30 +0200
        Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Balbir Singh <bsingharora@gmail.com> - 2016-08-31 12:20 +0200
        Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-08-31 13:00 +0200
        Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Alexey Kardashevskiy <aik@ozlabs.ru> - 2016-09-01 03:50 +0200
          Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Alexey Kardashevskiy <aik@ozlabs.ru> - 2016-09-01 14:20 +0200
  Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Oleg Nesterov <oleg@redhat.com> - 2016-08-30 15:00 +0200
    Re: [RFC][PATCH] Fix a race between rwsem and the scheduler Balbir Singh <bsingharora@gmail.com> - 2016-08-31 05:50 +0200

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