From: "Paul E. McKenney" <paulmck@kernel.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Boqun Feng <boqun.feng@gmail.com>,
Andrea Parri <parri.andrea@gmail.com>,
Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>,
will@kernel.org, peterz@infradead.org, npiggin@gmail.com,
dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr,
akiyks@gmail.com, dlustig@nvidia.com, joel@joelfernandes.org,
urezki@gmail.com, quic_neeraju@quicinc.com, frederic@kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] tools/memory-model: Make ppo a subrelation of po
Date: Sun, 29 Jan 2023 20:43:05 -0800 [thread overview]
Message-ID: <20230130044305.GO2948950@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <Y9co8OxyRehs8mob@rowland.harvard.edu>
On Sun, Jan 29, 2023 at 09:18:24PM -0500, Alan Stern wrote:
> On Sun, Jan 29, 2023 at 03:09:00PM -0800, Paul E. McKenney wrote:
> > On Sun, Jan 29, 2023 at 01:43:53PM -0800, Boqun Feng wrote:
> > > 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!
>
> Actually that's only part of it. The other part is rather obscure:
>
> (* Generate all co relations, including LKW events but not UL *)
> let co0 = co0 | ([IW] ; loc ; [LKW]) |
> (([LKW] ; loc ; [UNMATCHED-LKW]) \ [UNMATCHED-LKW])
>
> Implicitly this says that any lock with no corresponding unlock must
> come last in the coherence order, which implies the unmatched-locks rule
> (since only one lock event can be last). By itself, the unmatched-locks
> rule would not prevent P3 from executing before P1, provided P1 executes
> both its lock and unlock.
And thank you, Alan, as well!
And RCU looks to operate in a similar manner:
------------------------------------------------------------------------
C rcudeadlock
{
}
P0(int *a, int *b)
{
rcu_read_lock();
WRITE_ONCE(*a, 1);
synchronize_rcu();
WRITE_ONCE(*b, 1);
rcu_read_unlock();
}
P1(int *a, int *b)
{
int r1;
int r2;
r1 = READ_ONCE(*b);
smp_mb();
r2 = READ_ONCE(*a);
}
exists (1:r1=1 /\ 1:r2=0)
------------------------------------------------------------------------
$ herd7 -conf linux-kernel.cfg rcudeadlock.litmus
Test rcudeadlock Allowed
States 0
No
Witnesses
Positive: 0 Negative: 0
Condition exists (1:r1=1 /\ 1:r2=0)
Observation rcudeadlock Never 0 0
Time rcudeadlock 0.00
Hash=4f7f336ad39d724d93b089133b00d1e2
------------------------------------------------------------------------
So good enough! ;-)
Thanx, Paul
next prev parent reply other threads:[~2023-01-30 4:43 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-26 13:46 [PATCH v2 0/2] Streamlining treatment of smp_mb__after_unlock_lock Jonas Oberhauser
2023-01-26 13:46 ` [PATCH v2 1/2] tools/memory-model: Unify UNLOCK+LOCK pairings to po-unlock-lock-po Jonas Oberhauser
2023-01-26 16:36 ` Alan Stern
2023-01-26 20:08 ` Paul E. McKenney
2023-01-26 23:21 ` Paul E. McKenney
2023-01-27 13:18 ` Jonas Oberhauser
2023-01-27 15:13 ` Paul E. McKenney
2023-01-27 15:57 ` Jonas Oberhauser
2023-01-27 16:48 ` Paul E. McKenney
2023-01-26 13:46 ` [PATCH v2 2/2] tools/memory-model: Make ppo a subrelation of po Jonas Oberhauser
2023-01-26 16:36 ` Alan Stern
2023-01-27 14:31 ` Jonas Oberhauser
2023-01-28 19:56 ` Alan Stern
2023-01-28 22:14 ` Andrea Parri
2023-01-28 22:21 ` Andrea Parri
2023-01-28 22:59 ` Alan Stern
2023-01-29 5:17 ` Paul E. McKenney
2023-01-29 16:03 ` Alan Stern
2023-01-29 16:21 ` Paul E. McKenney
2023-01-29 17:28 ` Andrea Parri
2023-01-29 18:44 ` Paul E. McKenney
2023-01-29 21:43 ` Boqun Feng
2023-01-29 23:09 ` Paul E. McKenney
2023-01-30 2:18 ` Alan Stern
2023-01-30 4:43 ` Paul E. McKenney [this message]
2023-01-29 19:17 ` Paul E. McKenney
2023-01-29 17:11 ` Andrea Parri
2023-01-29 22:10 ` Alan Stern
2023-01-29 22:19 ` Jonas Oberhauser
2023-01-30 2:39 ` Alan Stern
2023-01-30 4:36 ` Paul E. McKenney
2023-01-30 16:47 ` Alan Stern
2023-01-30 16:50 ` Paul E. McKenney
2023-01-31 13:56 ` Jonas Oberhauser
2023-01-31 15:06 ` Alan Stern
2023-01-31 15:33 ` Jonas Oberhauser
2023-01-31 16:55 ` Alan Stern
2023-02-01 10:37 ` Jonas Oberhauser
2023-01-30 4:46 ` Paul E. McKenney
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