Messages in this thread | | | Date | Tue, 19 Dec 2017 11:05:44 -0500 (EST) | From | Alan Stern <> | Subject | Re: Prototype patch for Linux-kernel memory model |
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On Tue, 19 Dec 2017, afzal mohammed wrote:
> Hi, > > A trivial & late (sorry) comment, > > On Wed, Nov 15, 2017 at 08:37:49AM -0800, Paul E. McKenney wrote: > > > +THE HAPPENS-BEFORE RELATION: hb > > +------------------------------- > > > +Less trivial examples of prop all involve fences. Unlike the simple > > +examples above, they can require that some instructions are executed > > +out of program order. This next one should look familiar: > > + > > + int buf = 0, flag = 0; > > + > > + P0() > > + { > > + WRITE_ONCE(buf, 1); > > + smp_wmb(); > > + WRITE_ONCE(flag, 1); > > + } > > + > > + P1() > > + { > > + int r1; > > + int r2; > > + > > + r1 = READ_ONCE(flag); > > + r2 = READ_ONCE(buf); > > + } > > + > > +This is the MP pattern again, with an smp_wmb() fence between the two > > +stores. If r1 = 1 and r2 = 0 at the end then there is a prop link > > +from P1's second load to its first (backwards!). The reason is > > +similar to the previous examples: The value P1 loads from buf gets > > +overwritten by P1's store to buf, > > P0's store to buf > > afzal
Thank you; I have applied the change.
Alan Stern
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