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

From	Benjamin Herrenschmidt <benh@kernel.crashing.org>
Newsgroups	linux.kernel
Subject	Re: [RFC][PATCH] Fix a race between rwsem and the scheduler
Date	2016-08-31 23:50 +0200
Message-ID	<sclyp-7Kc-23@gated-at.bofh.it> (permalink)
References	(3 earlier) <sbS3o-5Yg-15@gated-at.bofh.it> <sbUye-7qR-15@gated-at.bofh.it> <sbW6Z-8w9-9@gated-at.bofh.it> <sbYLv-1Qd-11@gated-at.bofh.it> <scdUe-2XV-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, 2016-08-31 at 15:31 +0200, Peter Zijlstra wrote:
> On Wed, Aug 31, 2016 at 07:28:18AM +1000, Benjamin Herrenschmidt
> wrote:
> 
> > 
> > On powerpc we have a sync deep in _switch to achieve that.
> 
> OK, for giggles, could you (or Balbir) check what happens if you take
> that sync out?
> 
> There should be enough serialization in the generic code to cover the
> case that code mentions.
> 
> ARM64 has a stronger barrier in its context switch code, but that's
> because they need to sync against external agents (like their TLB and
> cache) and no amount of generic locking is going to cover that.

The problem is no amount of testing can tell you it works for sure :-)

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...

Cheers,
Ben.

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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