rcu/kvfree: Use READ_ONCE() when access to krcp->head

The need_offload_krc() function is now lock-free, which gives the
compiler freedom to load old values from plain C-language loads from
the kfree_rcu_cpu struture's ->head pointer.  This commit therefore
applied READ_ONCE() to these loads.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 735312f78e9801e5c8b85acbddc763e1690fc082..02551e0e11328a8020b06ba25838936b55b6de3e 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3165,7 +3165,7 @@ need_offload_krc(struct kfree_rcu_cpu *krcp)
                if (!list_empty(&krcp->bulk_head[i]))
                        return true;
 
-       return !!krcp->head;
+       return !!READ_ONCE(krcp->head);
 }
 
 static void
@@ -3206,7 +3206,7 @@ static void kfree_rcu_monitor(struct work_struct *work)
                // in that case the monitor work is rearmed.
                if ((!list_empty(&krcp->bulk_head[0]) && list_empty(&krwp->bulk_head_free[0])) ||
                        (!list_empty(&krcp->bulk_head[1]) && list_empty(&krwp->bulk_head_free[1])) ||
-                               (krcp->head && !krwp->head_free)) {
+                               (READ_ONCE(krcp->head) && !krwp->head_free)) {
 
                        // Channel 1 corresponds to the SLAB-pointer bulk path.
                        // Channel 2 corresponds to vmalloc-pointer bulk path.