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Groups > linux.kernel > #1493676
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability |
| Date | 2016-09-29 20:50 +0200 |
| Message-ID | <smOz8-7MS-9@gated-at.bofh.it> (permalink) |
| References | (3 earlier) <smMH0-6yY-21@gated-at.bofh.it> <smNa1-6Yg-19@gated-at.bofh.it> <smNjI-71u-21@gated-at.bofh.it> <smNWq-7uF-17@gated-at.bofh.it> <smO65-7D0-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Thu, Sep 29, 2016 at 11:10:15AM -0700, Paul E. McKenney wrote:
> > >
> > > P0(int *x, int *y)
> > > {
> > > WRITE_ONCE(*x, 1);
> > > smp_wmb();
> > > smp_store_release(y, 1);
> > > }
> > >
> > > P1(int *y)
> > > {
> > > WRITE_ONCE(*y, 2);
> > > }
> > >
> > > P2(int *x, int *y)
> > > {
> > > r1 = smp_load_acquire(y);
> > > r2 = READ_ONCE(*x);
> > > }
> > >
> > > Both ARM and powerpc allow the "after the dust settles" outcome (r1=2 &&
> > > r2=0), as does the current version of the early prototype Linux-kernel
> >
> > And the above needs to be (r1!=2 || r2 != 0)... Sigh!
>
> Make that (y==2 && r1==2 && r2 == 0).
>
> Any further bids? ;-)
Isn't that the trivial P1,P2,P0 order again?
How about something like so on PPC?
P0(int *x, int *y)
{
WRITE_ONCE(*x, 1);
smp_store_release(y, 1);
}
P1(int *x, int *y)
{
WRITE_ONCE(x, 2);
smp_store_release(y, 2);
}
P2(int *x, int *y)
{
r1 = smp_load_acquire(y);
r2 = READ_ONCE(*x);
}
(((x==1 && y==2) | (x==2 && y==1)) && (r1==1 || r1==2) && r2==0)
If you execute P0 and P1 concurrently and one store of each 'wins' the
LWSYNC of either is null and void, and therefore P2 is unordered and can
observe r2==0.
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Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Peter Zijlstra <peterz@infradead.org> - 2016-09-29 18:00 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Will Deacon <will.deacon@arm.com> - 2016-09-29 18:10 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Peter Zijlstra <peterz@infradead.org> - 2016-09-29 18:20 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-29 18:50 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-29 18:50 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Will Deacon <will.deacon@arm.com> - 2016-09-29 19:20 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-29 19:30 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-29 20:10 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-29 20:20 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Peter Zijlstra <peterz@infradead.org> - 2016-09-29 20:50 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-29 21:20 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Alan Stern <stern@rowland.harvard.edu> - 2016-09-29 21:40 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-29 22:30 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Peter Zijlstra <peterz@infradead.org> - 2016-09-30 11:00 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Peter Zijlstra <peterz@infradead.org> - 2016-09-30 11:10 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Peter Zijlstra <peterz@infradead.org> - 2016-09-30 12:00 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-30 14:20 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Peter Zijlstra <peterz@infradead.org> - 2016-09-30 15:00 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-30 15:40 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Boqun Feng <boqun.feng@gmail.com> - 2016-09-30 08:00 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Will Deacon <will.deacon@arm.com> - 2016-09-30 11:30 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-30 13:40 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Peter Zijlstra <peterz@infradead.org> - 2016-09-30 12:30 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-30 14:20 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Peter Zijlstra <peterz@infradead.org> - 2016-09-30 14:50 +0200
Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-30 15:20 +0200
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