Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/memory-model/linux-kernel.def b/tools/memory-model/linux-kernel.def
index 6fa3eb2..ef0f3c1 100644
--- a/tools/memory-model/linux-kernel.def
+++ b/tools/memory-model/linux-kernel.def
@@ -23,6 +23,8 @@
 smp_mb__before_atomic() { __fence{before-atomic}; }
 smp_mb__after_atomic() { __fence{after-atomic}; }
 smp_mb__after_spinlock() { __fence{after-spinlock}; }
+smp_mb__after_unlock_lock() { __fence{after-unlock-lock}; }
+barrier() { __fence{barrier}; }
 
 // Exchange
 xchg(X,V)  __xchg{mb}(X,V)
@@ -46,6 +48,12 @@
 synchronize_rcu() { __fence{sync-rcu}; }
 synchronize_rcu_expedited() { __fence{sync-rcu}; }
 
+// SRCU
+srcu_read_lock(X)  __srcu{srcu-lock}(X)
+srcu_read_unlock(X,Y) { __srcu{srcu-unlock}(X,Y); }
+synchronize_srcu(X)  { __srcu{sync-srcu}(X); }
+synchronize_srcu_expedited(X)  { __srcu{sync-srcu}(X); }
+
 // Atomic
 atomic_read(X) READ_ONCE(*X)
 atomic_set(X,V) { WRITE_ONCE(*X,V); }