The rcu-fence relation in the Linux Kernel Memory Model is not well
named. It doesn't act like any other fence relation, in that it does
not relate events before a fence to events after that fence. All it
does is relate certain RCU events to one another (those that are
ordered by the RCU Guarantee); this induces an actual
strong-fence-like relation linking events preceding the first RCU
event to those following the second.
This patch renames rcu-fence, now called rcu-order. It adds a new
definition of rcu-fence, something which should have been present all
along because it is used in the rb relation. And it modifies the
fence and strong-fence relations by making them incorporate the new
rcu-fence.
As a result of this change, there is no longer any need to define
full-fence in the section for detecting data races. It can simply be
replaced by the updated strong-fence relation.
This change should have no effect on the operation of the memory model.
Signed-off-by: Alan Stern <st...@rowland.harvard.edu>
---
tools/memory-model/linux-kernel.cat | 23 +++++++++++++----------
1 file changed, 13 insertions(+), 10 deletions(-)
Index: usb-devel/tools/memory-model/linux-kernel.cat
===================================================================
--- usb-devel.orig/tools/memory-model/linux-kernel.cat
+++ usb-devel/tools/memory-model/linux-kernel.cat
@@ -124,24 +124,28 @@ let rcu-link = po? ; hb* ; pb* ; prop ;
(*
* Any sequence containing at least as many grace periods as RCU read-side
- * critical sections (joined by rcu-link) acts as a generalized strong fence.
+ * critical sections (joined by rcu-link) induces order like a generalized
+ * inter-CPU strong fence.
* Likewise for SRCU grace periods and read-side critical sections, provided
* the synchronize_srcu() and srcu_read_[un]lock() calls refer to the same
* struct srcu_struct location.
*)
-let rec rcu-fence = rcu-gp | srcu-gp |
+let rec rcu-order = rcu-gp | srcu-gp |
(rcu-gp ; rcu-link ; rcu-rscsi) |
((srcu-gp ; rcu-link ; srcu-rscsi) & loc) |
(rcu-rscsi ; rcu-link ; rcu-gp) |
((srcu-rscsi ; rcu-link ; srcu-gp) & loc) |
- (rcu-gp ; rcu-link ; rcu-fence ; rcu-link ; rcu-rscsi) |
- ((srcu-gp ; rcu-link ; rcu-fence ; rcu-link ; srcu-rscsi) & loc) |
- (rcu-rscsi ; rcu-link ; rcu-fence ; rcu-link ; rcu-gp) |
- ((srcu-rscsi ; rcu-link ; rcu-fence ; rcu-link ; srcu-gp) & loc) |
- (rcu-fence ; rcu-link ; rcu-fence)
+ (rcu-gp ; rcu-link ; rcu-order ; rcu-link ; rcu-rscsi) |
+ ((srcu-gp ; rcu-link ; rcu-order ; rcu-link ; srcu-rscsi) & loc) |
+ (rcu-rscsi ; rcu-link ; rcu-order ; rcu-link ; rcu-gp) |
+ ((srcu-rscsi ; rcu-link ; rcu-order ; rcu-link ; srcu-gp) & loc) |
+ (rcu-order ; rcu-link ; rcu-order)
+let rcu-fence = po ; rcu-order ; po?
+let fence = fence | rcu-fence
+let strong-fence = strong-fence | rcu-fence
(* rb orders instructions just as pb does *)
-let rb = prop ; po ; rcu-fence ; po? ; hb* ; pb* ; [Marked]
+let rb = prop ; rcu-fence ; hb* ; pb* ; [Marked]
irreflexive rb as rcu
@@ -165,9 +169,8 @@ flag ~empty mixed-accesses as mixed-acce
(* Executes-before and visibility *)
let xbstar = (hb | pb | rb)*
-let full-fence = strong-fence | (po ; rcu-fence ; po?)
let vis = cumul-fence* ; rfe? ; [Marked] ;
- ((full-fence ; [Marked] ; xbstar) | (xbstar & int))
+ ((strong-fence ; [Marked] ; xbstar) | (xbstar & int))
(* Boundaries for lifetimes of plain accesses *)
let w-pre-bounded = [Marked] ; (addr | fence)?
