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Documentation/litmus-tests/atomic: Add a test for smp_mb__after_atomic()

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We already use a litmus test in atomic_t.txt to describe atomic RMW +
smp_mb__after_atomic() is stronger than acquire (both the read and the
write parts are ordered). So make it a litmus test in atomic-tests
directory, so that people can access the litmus easily.

Additionally, change the processor numbers "P1, P2" to "P0, P1" in
atomic_t.txt for the consistency with the processor numbers in the
litmus test, which herd can handle.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Boqun Feng 2020-03-26 10:40:22 +08:00 committed by Paul E. McKenney
parent 4dcd4d36dd
commit e30d023555
3 changed files with 42 additions and 5 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

10
Documentation/atomic_t.txt
View file

@ -233,19 +233,19 @@ as well. Similarly, something like:
is an ACQUIRE pattern (though very much not typical), but again the barrier is
strictly stronger than ACQUIRE. As illustrated:
C strong-acquire
C Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
{
}
P1(int *x, atomic_t *y)
P0(int *x, atomic_t *y)
{
r0 = READ_ONCE(*x);
smp_rmb();
r1 = atomic_read(y);
}
P2(int *x, atomic_t *y)
P1(int *x, atomic_t *y)
{
atomic_inc(y);
smp_mb__after_atomic();
@ -253,14 +253,14 @@ strictly stronger than ACQUIRE. As illustrated:
}
exists
(r0=1 /\ r1=0)
(0:r0=1 /\ 0:r1=0)
This should not happen; but a hypothetical atomic_inc_acquire() --
(void)atomic_fetch_inc_acquire() for instance -- would allow the outcome,
because it would not order the W part of the RMW against the following
WRITE_ONCE. Thus:
P1 P2
P0 P1
t = LL.acq *y (0)
t++;

32
Documentation/litmus-tests/atomic/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus Normal file
View file

@ -0,0 +1,32 @@
C Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
(*
* Result: Never
*
* Test that an atomic RMW followed by a smp_mb__after_atomic() is
* stronger than a normal acquire: both the read and write parts of
* the RMW are ordered before the subsequential memory accesses.
*)
{
}
P0(int *x, atomic_t *y)
{
int r0;
int r1;
r0 = READ_ONCE(*x);
smp_rmb();
r1 = atomic_read(y);
}
P1(int *x, atomic_t *y)
{
atomic_inc(y);
smp_mb__after_atomic();
WRITE_ONCE(*x, 1);
}
exists
(0:r0=1 /\ 0:r1=0)

5
Documentation/litmus-tests/atomic/README
View file

@ -7,5 +7,10 @@ tools/memory-model/README.
LITMUS TESTS
============
Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
Test that an atomic RMW followed by a smp_mb__after_atomic() is
stronger than a normal acquire: both the read and write parts of
the RMW are ordered before the subsequential memory accesses.
Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
Test that atomic_set() cannot break the atomicity of atomic RMWs.