From: Alan Huang <mmpgouride@gmail.com>
To: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
rcu@vger.kernel.org
Subject: Question about ISA2+pooncelock+pooncelock+pombonce litmus
Date: Mon, 18 Mar 2024 01:47:43 +0800 [thread overview]
Message-ID: <12E5C279-ADB1-463E-83E2-0A4F5D193754@gmail.com> (raw)
Hi,
I’m playing with the LKMM, then I saw the ISA2+pooncelock+pooncelock+pombonce.
The original litmus is as follows:
------------------------------------------------------
P0(int *x, int *y, spinlock_t *mylock)
{
spin_lock(mylock);
WRITE_ONCE(*x, 1);
WRITE_ONCE(*y, 1);
spin_unlock(mylock);
}
P1(int *y, int *z, spinlock_t *mylock)
{
int r0;
spin_lock(mylock);
r0 = READ_ONCE(*y);
WRITE_ONCE(*z, 1);
spin_unlock(mylock);
}
P2(int *x, int *z)
{
int r1;
int r2;
r2 = READ_ONCE(*z);
smp_mb();
r1 = READ_ONCE(*x);
}
exists (1:r0=1 /\ 2:r2=1 /\ 2:r1=0)
------------------------------------------------------
Of course, the result is Never.
But when I delete P0’s spin_lock and P1’s spin_unlock:
-------------------------------------------------------
P0(int *x, int *y, spinlock_t *mylock)
{
WRITE_ONCE(*x, 1);
WRITE_ONCE(*y, 1);
spin_unlock(mylock);
}
P1(int *y, int *z, spinlock_t *mylock)
{
int r0;
spin_lock(mylock);
r0 = READ_ONCE(*y);
WRITE_ONCE(*z, 1);
}
P2(int *x, int *z)
{
int r1;
int r2;
r2 = READ_ONCE(*z);
smp_mb();
r1 = READ_ONCE(*x);
}
exists (1:r0=1 /\ 2:r2=1 /\ 2:r1=0)
------------------------------------------------------
Then herd told me the result is Sometimes.
Is this expected?
next reply other threads:[~2024-03-17 17:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-17 17:47 Alan Huang [this message]
2024-03-17 23:02 ` Question about ISA2+pooncelock+pooncelock+pombonce litmus Paul E. McKenney
2024-03-18 11:19 ` Alan Huang
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