[tip:locking/core] tools/memory-model: Add model support for spin_is_locked()

From: tip-bot for Luc Maranget
Date: Tue May 15 2018 - 02:32:35 EST

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Commit-ID: 15553dcbca0638de57047e79b9fb4ea77aa04db3
Gitweb: https://git.kernel.org/tip/15553dcbca0638de57047e79b9fb4ea77aa04db3
Author: Luc Maranget <Luc.Maranget@xxxxxxxx>
AuthorDate: Mon, 14 May 2018 16:33:48 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 15 May 2018 08:11:17 +0200

tools/memory-model: Add model support for spin_is_locked()

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@xxxxxxx

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

Signed-off-by: Luc Maranget <luc.maranget@xxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Akira Yokosawa <akiyks@xxxxxxxxx>
Cc: Andrea Parri <parri.andrea@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Jade Alglave <j.alglave@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Luc Maranget <Luc.Maranget@xxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1526340837-12222-10-git-send-email-paulmck@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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(-)

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]) |

Next message: tip-bot for Paul E. McKenney: "[tip:locking/core] tools/memory-model: Flag "cumulativity" and "propagation" tests"
Previous message: tip-bot for Paul E. McKenney: "[tip:locking/core] tools/memory-model: Add scripts to test memory model"
In reply to: Paul E. McKenney: "[PATCH memory-model 10/19] tools/memory-model: Add model support for spin_is_locked"
Next in thread: Paul E. McKenney: "[PATCH memory-model 13/19] tools/memory-model: Improve comments in lock.cat"
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