On Thu, Feb 15, 2018 at 11:05:39PM +0100, Andrea Parri wrote: > On Thu, Feb 15, 2018 at 11:29:14AM -0800, Paul E. McKenney wrote: > > On Thu, Feb 15, 2018 at 12:51:56PM -0500, Alan Stern wrote: > > > On Fri, 16 Feb 2018, Akira Yokosawa wrote: > > > > > > > So, I attempted to rebase the patch to current (somewhat old) master of > > > > https://github.com/aparri/memory-model. Why? Because the lkmm branch > > > > in Paul's -rcu tree doesn't have linux-kernel-hardware.cat. > > > > > > > > However, after this change, Z6.0+pooncelock+pooncelock+pombonce still > > > > has the result "Sometimes". I must have done something wrong in the > > > > conflict resolution. > > > > > > > > Note: I have almost no idea what this patch is doing. I'm just hoping > > > > to give a starting point of a discussion. > > > > > > Yes, that litmus test gives "Sometimes" both with and without the > > > patch. But consider instead this slightly changed version of that > > > test, in which P2 reads Z instead of writing it: > > > > > > C Z6.0-variant > > > > > > {} > > > > > > P0(int *x, int *y, spinlock_t *mylock) > > > { > > > spin_lock(mylock); > > > WRITE_ONCE(*x, 1); > > > WRITE_ONCE(*y, 1); > > > spin_unlock(mylock); > > > } > > > > > > P1(int *y, int *z, spinlock_t *mylock) > > > { > > > int r0; > > > > > > spin_lock(mylock); > > > r0 = READ_ONCE(*y); > > > WRITE_ONCE(*z, 1); > > > spin_unlock(mylock); > > > } > > > > > > P2(int *x, int *z) > > > { > > > int r1; > > > int r2; > > > > > > r2 = READ_ONCE(*z); > > > smp_mb(); > > > r1 = READ_ONCE(*x); > > > } > > > > > > exists (1:r0=1 /\ 2:r2=1 /\ 2:r1=0) > > > > > > Without the patch, this test gives "Sometimes"; with the patch it gives > > > "Never". That is what I thought Paul was talking about originally. > > > > > > Sorry if my misunderstanding caused too much confusion for other > > > people. > > > > Ah, I did indeed get confused. I have changed the "Result:" for > > Z6.0+pooncelock+pooncelock+pombonce.litmus back to "Never", as in > > the patch below (which I merged into the patch adding all the > > comments). > > > > I have added the above test as ISA2+pooncelock+pooncelock+pombonce.litmus, > > with the Result: of Sometimes with you (Alan) as author and with your > > Signed-off-by -- please let me know if you would prefer some other > > approach. > > > > Please change the Result: when sending the proposed patch. Or please let > > me know if you would like me to apply the forward-port that Akira sent, > > in which case I will add the Result: change to that patch. Or for that > > matter, Akira might repost his forward-port of your patch with this change. > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit b2950420e1154131c0667f1ac58666bad3a06a69 > > Author: Paul E. McKenney <paul...@linux.vnet.ibm.com> > > Date: Thu Feb 15 10:35:25 2018 -0800 > > > > fixup! EXP litmus_tests: Add comments explaining tests' purposes > > > > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > > > > diff --git > > a/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus > > > > b/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus > > index fad47258a3e3..95890669859b 100644 > > --- > > a/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus > > +++ > > b/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus > > @@ -1,7 +1,7 @@ > > C Z6.0+pooncelock+pooncelock+pombonce > > > > (* > > - * Result: Never > > + * Result: Somtimes > > nit: s/Somtimes/Sometimes
Good catch, fixed! Thanx, Paul > Andrea > > > > * > > * This example demonstrates that a pair of accesses made by different > > * processes each while holding a given lock will not necessarily be > > >