sched/numa: Fix boot crash on arm64 systems

Qian Cai reported a boot crash on arm64 systems, caused by:

  0fb3978b0aac ("sched/numa: Fix NUMA topology for systems with CPU-less nodes")

The bug is that node_state() must be supplied a valid node_states[] array index,
but in task_numa_placement() the max_nid search can fail with NUMA_NO_NODE,
which is not a valid index.

Fix it by checking that max_nid is a valid index.

[ mingo: Added changelog. ]

Fixes: 0fb3978b0aac ("sched/numa: Fix NUMA topology for systems with CPU-less nodes")
Reported-by: Qian Cai <quic_qiancai@quicinc.com>
Tested-by: Qian Cai <quic_qiancai@quicinc.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 89d21fd..ee0664c 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2437,7 +2437,7 @@ static void task_numa_placement(struct task_struct *p)
        }
 
        /* Cannot migrate task to CPU-less node */
-       if (!node_state(max_nid, N_CPU)) {
+       if (max_nid != NUMA_NO_NODE && !node_state(max_nid, N_CPU)) {
                int near_nid = max_nid;
                int distance, near_distance = INT_MAX;