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Groups > linux.kernel > #1473086

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

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [RFC][PATCH] Fix a race between rwsem and the scheduler
Date 2016-08-31 09:30 +0200
Message-ID <sc889-7Pb-15@gated-at.bofh.it> (permalink)
References <sbMU2-2tK-13@gated-at.bofh.it> <sbQbf-4Ec-17@gated-at.bofh.it> <sbQXD-5kV-19@gated-at.bofh.it> <sbYLv-1Qd-1@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Wed, Aug 31, 2016 at 07:25:01AM +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2016-08-30 at 15:04 +0200, Oleg Nesterov wrote:
> > 
> > Confused... how this connects to UNLOCK+LOCK on rq->lock? A LOAD can
> > leak into the critical section.
> > 
> > But context switch should imply mb() we can rely on?
> 
> Between setting of ->on_rq and returning to the task so it can
> change its state back to [UN]INTERRUPTIBLE, there will be at least one
> write barrier (spin unlock of the rq),

spin-unlock is _not_ a write barrier, its a RELEASE barrier, and is not
sufficient for this.

> possibly even a full barrier
> (context switch). The write barrier is enough so I didn't dig to make
> sure we always context switch in the scenario we're looking at but I
> think we do.

There is enough, you just need to pair the RELEASE with an ACQUIRE to
get a full load-store barrier.

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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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