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    Subject[PATCH memory-model 10/19] tools/memory-model: Add model support for spin_is_locked
    Date
    From: Luc Maranget <Luc.Maranget@inria.fr>

    This commit first adds a trivial macro for spin_is_locked() to
    linux-kernel.def.

    It also adds cat code for enumerating all possible matches of lock
    write events (set LKW) with islocked events returning true (set RL,
    for Read from Lock), and unlock write events (set UL) with islocked
    events returning false (set RU, for Read from Unlock). Note that this
    intentionally does not model uniprocessor kernels (CONFIG_SMP=n) built
    with CONFIG_DEBUG_SPINLOCK=n, in which spin_is_locked() unconditionally
    returns zero.

    It also adds a pair of litmus tests demonstrating the minimal ordering
    provided by spin_is_locked() in conjunction with spin_lock(). Will Deacon
    noted that this minimal ordering happens on ARMv8:
    https://lkml.kernel.org/r/20180226162426.GB17158@arm.com

    Notice that herd7 installations strictly older than version 7.49
    do not handle the new constructs.

    Signed-off-by: Luc Maranget <luc.maranget@inria.fr>
    Cc: Alan Stern <stern@rowland.harvard.edu>
    Cc: Andrea Parri <parri.andrea@gmail.com>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Boqun Feng <boqun.feng@gmail.com>
    Cc: Nicholas Piggin <npiggin@gmail.com>
    Cc: David Howells <dhowells@redhat.com>
    Cc: Jade Alglave <j.alglave@ucl.ac.uk>
    Cc: Luc Maranget <luc.maranget@inria.fr>
    Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    Cc: Akira Yokosawa <akiyks@gmail.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
    ---
    tools/memory-model/linux-kernel.def | 1 +
    .../MP+polockmbonce+poacquiresilsil.litmus | 35 ++++++++++++++
    .../MP+polockonce+poacquiresilsil.litmus | 34 ++++++++++++++
    tools/memory-model/litmus-tests/README | 10 ++++
    tools/memory-model/lock.cat | 53 ++++++++++++++++++++--
    5 files changed, 129 insertions(+), 4 deletions(-)
    create mode 100644 tools/memory-model/litmus-tests/MP+polockmbonce+poacquiresilsil.litmus
    create mode 100644 tools/memory-model/litmus-tests/MP+polockonce+poacquiresilsil.litmus

    diff --git a/tools/memory-model/linux-kernel.def b/tools/memory-model/linux-kernel.def
    index 6bd3bc431b3d..f0553bd37c08 100644
    --- a/tools/memory-model/linux-kernel.def
    +++ b/tools/memory-model/linux-kernel.def
    @@ -38,6 +38,7 @@ cmpxchg_release(X,V,W) __cmpxchg{release}(X,V,W)
    spin_lock(X) { __lock(X); }
    spin_unlock(X) { __unlock(X); }
    spin_trylock(X) __trylock(X)
    +spin_is_locked(X) __islocked(X)

    // RCU
    rcu_read_lock() { __fence{rcu-lock}; }
    diff --git a/tools/memory-model/litmus-tests/MP+polockmbonce+poacquiresilsil.litmus b/tools/memory-model/litmus-tests/MP+polockmbonce+poacquiresilsil.litmus
    new file mode 100644
    index 000000000000..50f4d62bbf0e
    --- /dev/null
    +++ b/tools/memory-model/litmus-tests/MP+polockmbonce+poacquiresilsil.litmus
    @@ -0,0 +1,35 @@
    +C MP+polockmbonce+poacquiresilsil
    +
    +(*
    + * Result: Never
    + *
    + * Do spinlocks combined with smp_mb__after_spinlock() provide order
    + * to outside observers using spin_is_locked() to sense the lock-held
    + * state, ordered by acquire? Note that when the first spin_is_locked()
    + * returns false and the second true, we know that the smp_load_acquire()
    + * executed before the lock was acquired (loosely speaking).
    + *)
    +
    +{
    +}
    +
    +P0(spinlock_t *lo, int *x)
    +{
    + spin_lock(lo);
    + smp_mb__after_spinlock();
    + WRITE_ONCE(*x, 1);
    + spin_unlock(lo);
    +}
    +
    +P1(spinlock_t *lo, int *x)
    +{
    + int r1;
    + int r2;
    + int r3;
    +
    + r1 = smp_load_acquire(x);
    + r2 = spin_is_locked(lo);
    + r3 = spin_is_locked(lo);
    +}
    +
    +exists (1:r1=1 /\ 1:r2=0 /\ 1:r3=1)
    diff --git a/tools/memory-model/litmus-tests/MP+polockonce+poacquiresilsil.litmus b/tools/memory-model/litmus-tests/MP+polockonce+poacquiresilsil.litmus
    new file mode 100644
    index 000000000000..abf81e7a0895
    --- /dev/null
    +++ b/tools/memory-model/litmus-tests/MP+polockonce+poacquiresilsil.litmus
    @@ -0,0 +1,34 @@
    +C MP+polockonce+poacquiresilsil
    +
    +(*
    + * Result: Sometimes
    + *
    + * Do spinlocks provide order to outside observers using spin_is_locked()
    + * to sense the lock-held state, ordered by acquire? Note that when the
    + * first spin_is_locked() returns false and the second true, we know that
    + * the smp_load_acquire() executed before the lock was acquired (loosely
    + * speaking).
    + *)
    +
    +{
    +}
    +
    +P0(spinlock_t *lo, int *x)
    +{
    + spin_lock(lo);
    + WRITE_ONCE(*x, 1);
    + spin_unlock(lo);
    +}
    +
    +P1(spinlock_t *lo, int *x)
    +{
    + int r1;
    + int r2;
    + int r3;
    +
    + r1 = smp_load_acquire(x);
    + r2 = spin_is_locked(lo);
    + r3 = spin_is_locked(lo);
    +}
    +
    +exists (1:r1=1 /\ 1:r2=0 /\ 1:r3=1)
    diff --git a/tools/memory-model/litmus-tests/README b/tools/memory-model/litmus-tests/README
    index 04096fb8b8d9..6919909bbd0f 100644
    --- a/tools/memory-model/litmus-tests/README
    +++ b/tools/memory-model/litmus-tests/README
    @@ -63,6 +63,16 @@ LB+poonceonces.litmus
    MP+onceassign+derefonce.litmus
    As below, but with rcu_assign_pointer() and an rcu_dereference().

    +MP+polockmbonce+poacquiresilsil.litmus
    + Protect the access with a lock and an smp_mb__after_spinlock()
    + in one process, and use an acquire load followed by a pair of
    + spin_is_locked() calls in the other process.
    +
    +MP+polockonce+poacquiresilsil.litmus
    + Protect the access with a lock in one process, and use an
    + acquire load followed by a pair of spin_is_locked() calls
    + in the other process.
    +
    MP+polocks.litmus
    As below, but with the second access of the writer process
    and the first access of reader process protected by a lock.
    diff --git a/tools/memory-model/lock.cat b/tools/memory-model/lock.cat
    index ba4a4ec6d313..3b1439edc818 100644
    --- a/tools/memory-model/lock.cat
    +++ b/tools/memory-model/lock.cat
    @@ -5,7 +5,11 @@
    *)

    (* Generate coherence orders and handle lock operations *)
    -
    +(*
    + * Warning, crashes with herd7 versions strictly before 7.48.
    + * spin_islocked is functional from version 7.49.
    + *
    + *)
    include "cross.cat"

    (* From lock reads to their partner lock writes *)
    @@ -32,12 +36,16 @@ flag ~empty [M \ IW] ; loc ; [ALL-LOCKS] as mixed-lock-accesses
    (* The final value of a spinlock should not be tested *)
    flag ~empty [FW] ; loc ; [ALL-LOCKS] as lock-final

    -
    +(*
    + * Backward compatibility
    + *)
    +let RL = try RL with emptyset (* defined herd7 >= 7.49 *)
    +let RU = try RU with emptyset (* defined herd7 >= 7.49 *)
    (*
    * Put lock operations in their appropriate classes, but leave UL out of W
    * until after the co relation has been generated.
    *)
    -let R = R | LKR | LF
    +let R = R | LKR | LF | RL | RU
    let W = W | LKW

    let Release = Release | UL
    @@ -72,8 +80,45 @@ let all-possible-rfe-lf =

    (* Generate all rf relations for LF events *)
    with rfe-lf from cross(all-possible-rfe-lf)
    -let rf = rf | rfi-lf | rfe-lf

    +let rf-lf = rfe-lf | rfi-lf
    +
    +(* rf for RL events, ie islocked returning true, similar to LF above *)
    +
    +(* islocked returning true inside a critical section
    + * must read from the opening lock
    + *)
    +let rfi-rl = ([LKW] ; po-loc ; [RL]) \ ([LKW] ; po-loc ; [UL] ; po-loc)
    +
    +(* islocked returning true outside critical sections can match any
    + * external lock.
    + *)
    +let all-possible-rfe-rl =
    + let possible-rfe-lf r =
    + let pair-to-relation p = p ++ 0
    + in map pair-to-relation ((LKW * {r}) & loc & ext)
    + in map possible-rfe-lf (RL \ range(rfi-rl))
    +
    +with rfe-rl from cross(all-possible-rfe-rl)
    +let rf-rl = rfe-rl | rfi-rl
    +
    +(* Read from unlock, ie islocked returning false, slightly different *)
    +
    +(* islocked returning false can read from the last po-previous unlock *)
    +let rfi-ru = ([UL] ; po-loc ; [RU]) \ ([UL] ; po-loc ; [LKW] ; po-loc)
    +
    +(* any islocked returning false can read from any external unlock *)
    +let all-possible-rfe-ru =
    + let possible-rfe-ru r =
    + let pair-to-relation p = p ++ 0
    + in map pair-to-relation (((UL|IW) * {r}) & loc & ext)
    + in map possible-rfe-ru RU
    +
    +with rfe-ru from cross(all-possible-rfe-ru)
    +let rf-ru = rfe-ru | rfi-ru
    +
    +(* Final rf relation *)
    +let rf = rf | rf-lf | rf-rl | rf-ru

    (* Generate all co relations, including LKW events but not UL *)
    let co0 = co0 | ([IW] ; loc ; [LKW]) |
    --
    2.5.2
    \
     
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