1 files changed, 77 insertions, 30 deletions

diff --git a/tools/memory-model/lock.cat b/tools/memory-model/lock.cat
index ba4a4ec6d313..305ded17e741 100644
--- a/tools/memory-model/lock.cat
+++ b/tools/memory-model/lock.cat
@@ -4,46 +4,72 @@
  * Copyright (C) 2017 Alan Stern <stern@rowland.harvard.edu>
  *)
 
-(* Generate coherence orders and handle lock operations *)
+(*
+ * Generate coherence orders and handle lock operations
+ *
+ * Warning: spin_is_locked() crashes herd7 versions strictly before 7.48.
+ * spin_is_locked() is functional from herd7 version 7.49.
+ *)
 
 include "cross.cat"
 
-(* From lock reads to their partner lock writes *)
-let lk-rmw = ([LKR] ; po-loc ; [LKW]) \ (po ; po)
-let rmw = rmw | lk-rmw
-
 (*
- * A paired LKR must always see an unlocked value; spin_lock() calls nested
- * inside a critical section (for the same lock) always deadlock.
+ * The lock-related events generated by herd are as follows:
+ *
+ * LKR		Lock-Read: the read part of a spin_lock() or successful
+ *			spin_trylock() read-modify-write event pair
+ * LKW		Lock-Write: the write part of a spin_lock() or successful
+ *			spin_trylock() RMW event pair
+ * UL		Unlock: a spin_unlock() event
+ * LF		Lock-Fail: a failed spin_trylock() event
+ * RL		Read-Locked: a spin_is_locked() event which returns True
+ * RU		Read-Unlocked: a spin_is_locked() event which returns False
+ *
+ * LKR and LKW events always come paired, like all RMW event sequences.
+ *
+ * LKR, LF, RL, and RU are read events; LKR has Acquire ordering.
+ * LKW and UL are write events; UL has Release ordering.
+ * LKW, LF, RL, and RU have no ordering properties.
  *)
-empty ([LKW] ; po-loc ; [domain(lk-rmw)]) \ (po-loc ; [UL] ; po-loc)
-	as lock-nest
 
-(* The litmus test is invalid if an LKW event is not part of an RMW pair *)
-flag ~empty LKW \ range(lk-rmw) as unpaired-LKW
+(* Backward compatibility *)
+let RL = try RL with emptyset
+let RU = try RU with emptyset
 
-(* This will be allowed if we implement spin_is_locked() *)
-flag ~empty LKR \ domain(lk-rmw) as unpaired-LKR
+(* Treat RL as a kind of LF: a read with no ordering properties *)
+let LF = LF | RL
 
-(* There should be no R or W accesses to spinlocks *)
-let ALL-LOCKS = LKR | LKW | UL | LF
+(* There should be no ordinary R or W accesses to spinlocks *)
+let ALL-LOCKS = LKR | LKW | UL | LF | RU
 flag ~empty [M \ IW] ; loc ; [ALL-LOCKS] as mixed-lock-accesses
 
+(* Link Lock-Reads to their RMW-partner Lock-Writes *)
+let lk-rmw = ([LKR] ; po-loc ; [LKW]) \ (po ; po)
+let rmw = rmw | lk-rmw
+
+(* The litmus test is invalid if an LKR/LKW event is not part of an RMW pair *)
+flag ~empty LKW \ range(lk-rmw) as unpaired-LKW
+flag ~empty LKR \ domain(lk-rmw) as unpaired-LKR
+
+(*
+ * An LKR must always see an unlocked value; spin_lock() calls nested
+ * inside a critical section (for the same lock) always deadlock.
+ *)
+empty ([LKW] ; po-loc ; [LKR]) \ (po-loc ; [UL] ; po-loc) as lock-nest
+
 (* The final value of a spinlock should not be tested *)
 flag ~empty [FW] ; loc ; [ALL-LOCKS] as lock-final
 
-
 (*
  * 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 | RU
 let W = W | LKW
 
 let Release = Release | UL
 let Acquire = Acquire | LKR
 
-
 (* Match LKW events to their corresponding UL events *)
 let critical = ([LKW] ; po-loc ; [UL]) \ (po-loc ; [LKW | UL] ; po-loc)
 
@@ -53,27 +79,48 @@ flag ~empty UL \ range(critical) as unmatched-unlock
 let UNMATCHED-LKW = LKW \ domain(critical)
 empty ([UNMATCHED-LKW] ; loc ; [UNMATCHED-LKW]) \ id as unmatched-locks
 
-
 (* rfi for LF events: link each LKW to the LF events in its critical section *)
 let rfi-lf = ([LKW] ; po-loc ; [LF]) \ ([LKW] ; po-loc ; [UL] ; po-loc)
 
 (* rfe for LF events *)
 let all-possible-rfe-lf =
-  (*
-   * Given an LF event r, compute the possible rfe edges for that event
-   * (all those starting from LKW events in other threads),
-   * and then convert that relation to a set of single-edge relations.
-   *)
-  let possible-rfe-lf r =
-    let pair-to-relation p = p ++ 0
-    in map pair-to-relation ((LKW * {r}) & loc & ext)
-  (* Do this for each LF event r that isn't in rfi-lf *)
-  in map possible-rfe-lf (LF \ range(rfi-lf))
+	(*
+	 * Given an LF event r, compute the possible rfe edges for that event
+	 * (all those starting from LKW events in other threads),
+	 * and then convert that relation to a set of single-edge relations.
+	 *)
+	let possible-rfe-lf r =
+		let pair-to-relation p = p ++ 0
+		in map pair-to-relation ((LKW * {r}) & loc & ext)
+	(* Do this for each LF event r that isn't in rfi-lf *)
+	in map possible-rfe-lf (LF \ range(rfi-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
+
+(*
+ * RU, i.e., spin_is_locked() returning False, is slightly different.
+ * We rely on the memory model to rule out cases where spin_is_locked()
+ * within one of the lock's critical sections returns False.
+ *)
+
+(* rfi for RU events: an RU may read from the last po-previous UL *)
+let rfi-ru = ([UL] ; po-loc ; [RU]) \ ([UL] ; po-loc ; [LKW] ; po-loc)
+
+(* rfe for RU events: an RU may read from an external UL or the initial write *)
+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
+
+(* Generate all rf relations for RU events *)
+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-ru
 
 (* Generate all co relations, including LKW events but not UL *)
 let co0 = co0 | ([IW] ; loc ; [LKW]) |