Messages in this thread |  | | Date | Sun, 29 Jan 2023 15:09:00 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2 2/2] tools/memory-model: Make ppo a subrelation of po |
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On Sun, Jan 29, 2023 at 01:43:53PM -0800, Boqun Feng wrote: > On Sun, Jan 29, 2023 at 10:44:03AM -0800, Paul E. McKenney wrote: > > On Sun, Jan 29, 2023 at 06:28:27PM +0100, Andrea Parri wrote: > > > > Why can't P3's spin_lock() read from that initial write? > > > > > > Mmh, sounds like you want to play with something like below? > > > > > > Andrea > > > > > > diff --git a/tools/memory-model/lock.cat b/tools/memory-model/lock.cat > > > index 6b52f365d73ac..20c3af4511255 100644 > > > --- a/tools/memory-model/lock.cat > > > +++ b/tools/memory-model/lock.cat > > > @@ -74,7 +74,6 @@ flag ~empty UL \ range(critical) as unmatched-unlock > > > > > > (* Allow up to one unmatched LKW per location; more must deadlock *) > > > let UNMATCHED-LKW = LKW \ domain(critical) > > > -empty ([UNMATCHED-LKW] ; loc ; [UNMATCHED-LKW]) \ id as unmatched-locks > > > > > > (* rfi for LF events: link each LKW to the LF events in its critical section *) > > > let rfi-lf = ([LKW] ; po-loc ; [LF]) \ ([LKW] ; po-loc ; [UL] ; po-loc) > > > @@ -120,8 +119,7 @@ let rf-ru = rfe-ru | rfi-ru > > > let rf = rf | rf-lf | rf-ru > > > > > > (* Generate all co relations, including LKW events but not UL *) > > > -let co0 = co0 | ([IW] ; loc ; [LKW]) | > > > - (([LKW] ; loc ; [UNMATCHED-LKW]) \ [UNMATCHED-LKW]) > > > +let co0 = co0 | ([IW] ; loc ; [LKW]) > > > include "cos-opt.cat" > > > let W = W | UL > > > let M = R | W > > > > No idea. But the following litmus test gets no executions whatsoever, > > so point taken about my missing at least one corner case. ;-) > > > > Adding a spin_unlock() to the end of either process allows both to > > run. > > > > One could argue that this is a bug, but one could equally well argue > > that if you have a deadlock, you have a deadlock. > > > > in lock.cat: > > (* Allow up to one unmatched LKW per location; more must deadlock *) > let UNMATCHED-LKW = LKW \ domain(critical) > empty ([UNMATCHED-LKW] ; loc ; [UNMATCHED-LKW]) \ id as unmatched-locks > > we rule out deadlocks from the execution candidates we care about.
Thank you, Boqun!
Thanx, Paul
> Regards, > Boqun > > > Thoughts? > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > C lock > > > > { > > } > > > > > > P0(int *a, int *b, spinlock_t *l) > > { > > spin_lock(l); > > WRITE_ONCE(*a, 1); > > } > > > > P1(int *a, int *b, spinlock_t *l) > > { > > spin_lock(l); > > WRITE_ONCE(*b, 1); > > } > > > > exists (a=1 /\ b=1)
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