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.
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
