Re: Litmus test names

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Sat, Apr 08, 2023 at 08:57:57PM +0200, Jonas Oberhauser wrote:
> 
> On 4/8/2023 6:49 PM, Joel Fernandes wrote:
> > On Fri, Apr 07, 2023 at 05:49:02PM -0700, Paul E. McKenney wrote:
> > > On Fri, Apr 07, 2023 at 03:05:01PM +0200, Jonas Oberhauser wrote:
> > > > 
> > > > On 4/7/2023 2:12 AM, Joel Fernandes wrote:
> > > > > 
> > > > > > On Apr 6, 2023, at 6:34 PM, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:
> > > > > > 
> > > > > > On Thu, Apr 06, 2023 at 05:36:13PM -0400, Alan Stern wrote:
> > > > > > > Paul:
> > > > > > > 
> > > > > > > I just saw that two of the files in
> > > > > > > tools/memory-model/litmus-tests have
> > > > > > > almost identical names:
> > > > > > > 
> > > > > > >   Z6.0+pooncelock+pooncelock+pombonce.litmus
> > > > > > >   Z6.0+pooncelock+poonceLock+pombonce.litmus
> > > > > > > 
> > > > > > > They differ only by a lower-case 'l' vs. a capital 'L'.  It's
> > > > > > > not at all
> > > > > > > easy to see, and won't play well in case-insensitive filesystems.
> > > > > > > 
> > > > > > > Should one of them be renamed?
> > > > > > 
> > FWIW, if I move that smp_mb_after..() a step lower, that also makes the test
> > work (see below).
> > 
> > If you may look over quickly my analysis of why this smp_mb_after..() is
> > needed, it is because what I marked as a and d below don't have an hb
> > relation right?
> 
> I think a and d have an hb relation due to the
> a ->po-rel X ->rfe Y ->acq-po d
> edges (where X and Y are the unlock/lock events I annotated in your example
> below).
> 
> Generally, an mb_unlock_lock isn't used to give you hb, but to turn some
> (coe/fre) ; hb* edges into pb edges
> 
> In this case, that would probably be
> f ->fre a ->hb* f   (where a ->hb* f comes from a ->hb* d ->hb e ->hb f)
> By adding the mb_unlock_lock_po in one of the right places, this becomes f
> ->pb f,
> thus forbidden.

Yes, it is forbidden, and even on purpose.  ;-)

But please don't do this in real life.  Having that READ_ONCE(*y) be
ordered differently on different architectures is not what those reading
your code will want to deal with.

							Thanx, Paul

> Have fun,
> jonas
> 
> 
> > 
> > (*
> >    b ->rf c
> > 
> >    d ->co e
> > 
> >    e ->hb f
> > 
> >    basically the issue is a ->po b ->rf c ->po d    does not imply a ->hb d
> > *)
> > 
> > P0(int *x, int *y, spinlock_t *mylock)
> > {
> > 	spin_lock(mylock);
> > 	WRITE_ONCE(*x, 1); // a
> > 	WRITE_ONCE(*y, 1); // b
> > 	spin_unlock(mylock); // X
> > }
> > 
> > P1(int *y, int *z, spinlock_t *mylock)
> > {
> > 	int r0;
> > 
> > 	spin_lock(mylock); // Y
> > 	r0 = READ_ONCE(*y); // c
> > 	smp_mb__after_spinlock(); // moving this a bit lower also works fwiw.
> > 	WRITE_ONCE(*z, 1);  // d
> > 	spin_unlock(mylock);
> > }
> > 
> > P2(int *x, int *z)
> > {
> > 	int r1;
> > 
> > 	WRITE_ONCE(*z, 2);  // e
> > 	smp_mb();
> > 	r1 = READ_ONCE(*x); // f
> > }
> > 
> > exists (1:r0=1 /\ z=2 /\ 2:r1=0)
> > 
> > 
> > > Would someone like to to a "git mv" send the resulting patch?
> > Yes I can do that in return as I am thankful in advance for the above
> > discussion. ;)
> > 
> > thanks,
> > 
> >   - Joel
> > 
> 



[Index of Archives]     [Linux Kernel]     [Kernel Newbies]     [x86 Platform Driver]     [Netdev]     [Linux Wireless]     [Netfilter]     [Bugtraq]     [Linux Filesystems]     [Yosemite Discussion]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Device Mapper]

  Powered by Linux