Messages in this thread | | | Date | Fri, 18 Sep 2015 14:34:34 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] kernel: fix data race in put_pid |
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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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