Commit 556bb7d2 authored Feb 20, 2018 by Alan Stern Committed by Ingo Molnar Feb 21, 2018

tools/memory-model: Add a S lock-based external-view litmus test



This commit adds a litmus test in which P0() and P1() form a lock-based S
litmus test, with the addition of P2(), which observes P0()'s and P1()'s
accesses with a full memory barrier but without the lock.  This litmus
test asks whether writes carried out by two different processes under the
same lock will be seen in order by a third process not holding that lock.
The answer to this question is "yes" for all architectures supporting
the Linux kernel, but is "no" according to the current version of LKMM.

A patch to LKMM is under development.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akiyks@gmail.com
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: nborisov@suse.com
Cc: npiggin@gmail.com
Cc: parri.andrea@gmail.com
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1519169112-20593-10-git-send-email-paulmck@linux.vnet.ibm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 8f7f2fbd

tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus

0 → 100644

+41 −0

Original line number	Diff line number	Diff line
		C ISA2+pooncelock+pooncelock+pombonce.litmus

		(*
		* Result: Sometimes
		*
		* This test shows that the ordering provided by a lock-protected S
		* litmus test (P0() and P1()) are not visible to external process P2().
		* This is likely to change soon.
		*)

		{}

		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)

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