rcu: Correct READ_ONCE()/WRITE_ONCE() for ->rcu_read_unlock_special

The task_struct structure's ->rcu_read_unlock_special field is only ever
read or written by the owning task, but it is accessed both at process
and interrupt levels.  It may therefore be accessed using plain reads
and writes while interrupts are disabled, but must be accessed using
READ_ONCE() and WRITE_ONCE() or better otherwise.  This commit makes a
few adjustments to align with this discipline.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index ec4fb93a5dbe6ecc2761bb585a78854c0366cfe0..1ee0782213b8298fa9766676ec47172d78edb573 100644 (file)
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -633,7 +633,7 @@ static void rcu_exp_handler(void *unused)
                raw_spin_lock_irqsave_rcu_node(rnp, flags);
                if (rnp->expmask & rdp->grpmask) {
                        rdp->deferred_qs = true;
-                       WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, true);
+                       t->rcu_read_unlock_special.b.exp_hint = true;
                }
                raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
                return;

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 81d3cd821891bc2feaf7e6a5b682ee517ddab807..6ddb3c05e88f0a25ea64c44cb40eead4e530c1a0 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -285,7 +285,7 @@ static void rcu_qs(void)
                                       TPS("cpuqs"));
                __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
                barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
-               current->rcu_read_unlock_special.b.need_qs = false;
+               WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
        }
 }
 
@@ -817,7 +817,7 @@ void exit_rcu(void)
        if (unlikely(!list_empty(&current->rcu_node_entry))) {
                t->rcu_read_lock_nesting = 1;
                barrier();
-               t->rcu_read_unlock_special.b.blocked = true;
+               WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
        } else if (unlikely(t->rcu_read_lock_nesting)) {
                t->rcu_read_lock_nesting = 1;
        } else {