sched: Avoid NULL dereference on sd_busy

Commit 37dc6b50cee9 ("sched: Remove unnecessary iteration over sched
domains to update nr_busy_cpus") forgot to clear 'sd_busy' under some
conditions leading to a possible NULL deref in set_cpu_sd_state_idle().

Reported-by: Anton Blanchard <anton@samba.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20131118113701.GF3866@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c180860..a1591ca 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4910,8 +4910,9 @@ static void update_top_cache_domain(int cpu)
        if (sd) {
                id = cpumask_first(sched_domain_span(sd));
                size = cpumask_weight(sched_domain_span(sd));
-               rcu_assign_pointer(per_cpu(sd_busy, cpu), sd->parent);
+               sd = sd->parent; /* sd_busy */
        }
+       rcu_assign_pointer(per_cpu(sd_busy, cpu), sd);
 
        rcu_assign_pointer(per_cpu(sd_llc, cpu), sd);
        per_cpu(sd_llc_size, cpu) = size;