tools/memory-model: Expand definition of barrier

Commit 66be4e66 ("rcu: locking and unlocking need to always be at
least barriers") added compiler barriers back into rcu_read_lock() and
rcu_read_unlock().  Furthermore, srcu_read_lock() and
srcu_read_unlock() have always contained compiler barriers.

The Linux Kernel Memory Model ought to know about these barriers.
This patch adds them into the memory model.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

tools/memory-model/linux-kernel.cat

@@ -45,7 +45,8 @@ let strong-fence = mb | gp
 let nonrw-fence = strong-fence | po-rel | acq-po
 let fence = nonrw-fence | wmb | rmb
 let barrier = fencerel(Barrier | Rmb | Wmb | Mb | Sync-rcu | Sync-srcu |
-		Before-atomic | After-atomic | Acquire | Release) |
+		Before-atomic | After-atomic | Acquire | Release |
+		Rcu-lock | Rcu-unlock | Srcu-lock | Srcu-unlock) |
 	(po ; [Release]) | ([Acquire] ; po)
 
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