rcu-tasks: Handle sparse cpu_possible_mask in rcu_tasks_invoke_cbs()

If the cpu_possible_mask is sparse (for example, if bits are set only for
CPUs 0, 4, 8, ...), then rcu_tasks_invoke_cbs() will access per-CPU data
for a CPU not in cpu_possible_mask.  It makes these accesses while doing
a workqueue-based binary search for non-empty callback lists.  Although
this search must pass through CPUs not represented in cpu_possible_mask,
it has no need to check the callback list for such CPUs.

This commit therefore changes the rcu_tasks_invoke_cbs() function's
binary search so as to only check callback lists for CPUs present in
cpu_possible_mask.

Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index fd70d86..3925e32 100644 (file)
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -468,7 +468,7 @@ static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu
                }
        }
 
-       if (rcu_segcblist_empty(&rtpcp->cblist))
+       if (rcu_segcblist_empty(&rtpcp->cblist) || !cpu_possible(cpu))
                return;
        raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
        rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));