rcu: Protect rcu_node accesses during CPU stall warnings

The print_other_cpu_stall() function accesses a number of rcu_node
fields without protection from the ->lock.  In theory, this is not
a problem because the fields accessed are all integers, but in
practice the compiler can get nasty.  Therefore, the commit extends
the existing critical section to cover the entire loop body.

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

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 2c4ee4cdbc0e7c900c9603a69e1ed9c82075a1be..2cf8eb3e2d435828afb1e149606aa8277efee947 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -746,14 +746,15 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
        rcu_for_each_leaf_node(rsp, rnp) {
                raw_spin_lock_irqsave(&rnp->lock, flags);
                ndetected += rcu_print_task_stall(rnp);
+               if (rnp->qsmask != 0) {
+                       for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
+                               if (rnp->qsmask & (1UL << cpu)) {
+                                       print_cpu_stall_info(rsp,
+                                                            rnp->grplo + cpu);
+                                       ndetected++;
+                               }
+               }
                raw_spin_unlock_irqrestore(&rnp->lock, flags);
-               if (rnp->qsmask == 0)
-                       continue;
-               for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
-                       if (rnp->qsmask & (1UL << cpu)) {
-                               print_cpu_stall_info(rsp, rnp->grplo + cpu);
-                               ndetected++;
-                       }
        }
 
        /*