Re: [PATCH] kernel: fix data race in put_pid

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] kernel: fix data race in put_pid
Date	2015-09-18 14:50 +0200
Message-ID	<qa3h0-2Sw-21@gated-at.bofh.it> (permalink)
References	(5 earlier) <q9LWN-38s-1@gated-at.bofh.it> <q9ZGr-67w-31@gated-at.bofh.it> <q9ZQ6-6yg-13@gated-at.bofh.it> <qa0j8-78w-9@gated-at.bofh.it> <qa37k-2Hb-23@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, Sep 18, 2015 at 01:31:27PM +0100, James Hogan wrote:
> Hi Peter,
> 
> On Fri, Sep 18, 2015 at 11:27:32AM +0200, Peter Zijlstra wrote:
> > On Fri, Sep 18, 2015 at 10:57:32AM +0200, Peter Zijlstra wrote:
> > > diff --git a/arch/metag/include/asm/atomic_lnkget.h b/arch/metag/include/asm/atomic_lnkget.h
> > > index 21c4c268b86c..1bd21c933435 100644
> > > --- a/arch/metag/include/asm/atomic_lnkget.h
> > > +++ b/arch/metag/include/asm/atomic_lnkget.h
> > > @@ -3,7 +3,8 @@
> > >  
> > >  #define ATOMIC_INIT(i)	{ (i) }
> > >  
> > > -#define atomic_set(v, i)		((v)->counter = (i))
> > > +/* XXX: should be LNKSETD ? */
> > > +#define atomic_set(v, i)		WRITE_ONCE((v)->counter, (i))
> > >  
> > >  #include <linux/compiler.h>
> > >  
> > 
> > James?
> 
> It should be fine without a LNKSET. The only reason LNKGET is required
> for atomic_read() is that on certain cores the LNKGET/LNKSET
> instructions went around the cache, but those cores also have write
> through caches, so it shouldn't result in incoherence.
> 
> I've just double checked, and the pipeline seems to handle the linked
> read after write correctly, so e.g. after:
> 
> 0220002c    MOV       D0FrT,#0x5
> b6208042    SETD      [D1Ar3],D0FrT
> ad1080cc    LNKGETD   D0Ar4,[D1Ar3]
> 
> D0Ar4 is correct (0x5).

Thanks! XXX removed.
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Thread

[PATCH] kernel: fix data race in put_pid Dmitry Vyukov <dvyukov@google.com> - 2015-09-17 15:30 +0200
  Re: [PATCH] kernel: fix data race in put_pid Oleg Nesterov <oleg@redhat.com> - 2015-09-17 18:20 +0200
    Re: [PATCH] kernel: fix data race in put_pid Dmitry Vyukov <dvyukov@google.com> - 2015-09-17 18:50 +0200
      Re: [PATCH] kernel: fix data race in put_pid Oleg Nesterov <oleg@redhat.com> - 2015-09-17 19:50 +0200
        Re: [PATCH] kernel: fix data race in put_pid Dmitry Vyukov <dvyukov@google.com> - 2015-09-17 20:00 +0200
          Re: [PATCH] kernel: fix data race in put_pid Dmitry Vyukov <dvyukov@google.com> - 2015-09-17 20:10 +0200
          Re: [PATCH] kernel: fix data race in put_pid Oleg Nesterov <oleg@redhat.com> - 2015-09-17 20:20 +0200
            Re: [PATCH] kernel: fix data race in put_pid Dmitry Vyukov <dvyukov@google.com> - 2015-09-17 20:40 +0200
            Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 11:00 +0200
              Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 11:10 +0200
                Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 11:40 +0200
                Re: [PATCH] kernel: fix data race in put_pid James Hogan <james.hogan@imgtec.com> - 2015-09-18 14:40 +0200
                Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 14:50 +0200
                Re: [PATCH] kernel: fix data race in put_pid "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-09-18 18:40 +0200
              Re: [PATCH] kernel: fix data race in put_pid Dmitry Vyukov <dvyukov@google.com> - 2015-09-18 11:10 +0200
                Re: [PATCH] kernel: fix data race in put_pid Will Deacon <will.deacon@arm.com> - 2015-09-18 11:30 +0200
                Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 11:40 +0200
                Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 13:30 +0200
                Re: [PATCH] kernel: fix data race in put_pid Will Deacon <will.deacon@arm.com> - 2015-09-18 13:40 +0200
                Re: [PATCH] kernel: fix data race in put_pid Dmitry Vyukov <dvyukov@google.com> - 2015-09-18 14:00 +0200
                Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 14:10 +0200
                Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 14:30 +0200
                Re: [PATCH] kernel: fix data race in put_pid Will Deacon <will.deacon@arm.com> - 2015-09-18 14:50 +0200
                Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 15:20 +0200
                Re: [PATCH] kernel: fix data race in put_pid Oleg Nesterov <oleg@redhat.com> - 2015-09-18 15:50 +0200
                Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 16:00 +0200
                Re: [PATCH] kernel: fix data race in put_pid Dmitry Vyukov <dvyukov@google.com> - 2015-09-18 16:00 +0200
                Re: [PATCH] kernel: fix data race in put_pid Oleg Nesterov <oleg@redhat.com> - 2015-09-18 16:50 +0200
                Re: [PATCH] kernel: fix data race in put_pid Dmitry Vyukov <dvyukov@google.com> - 2015-09-22 10:40 +0200
                Re: [PATCH] kernel: fix data race in put_pid Eric Dumazet <eric.dumazet@gmail.com> - 2015-09-18 18:20 +0200
                Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 18:30 +0200
                Re: [PATCH] kernel: fix data race in put_pid "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-09-18 18:00 +0200
              Re: [PATCH] kernel: fix data race in put_pid Oleg Nesterov <oleg@redhat.com> - 2015-09-18 15:40 +0200
              Re: [PATCH] kernel: fix data race in put_pid Oleg Nesterov <oleg@redhat.com> - 2015-09-18 15:40 +0200
                Re: [PATCH] kernel: fix data race in put_pid Peter Zijlstra <peterz@infradead.org> - 2015-09-18 16:00 +0200
                Re: [PATCH] kernel: fix data race in put_pid Oleg Nesterov <oleg@redhat.com> - 2015-09-18 17:10 +0200
                Re: [PATCH] kernel: fix data race in put_pid Oleg Nesterov <oleg@redhat.com> - 2015-09-18 17:40 +0200
                Re: [PATCH] kernel: fix data race in put_pid "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-09-18 18:30 +0200
      Re: [PATCH] kernel: fix data race in put_pid "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-09-17 20:00 +0200

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