[tip: sched/core] sched/numa: Fix boot crash on arm64 systems

[tip-bot2 for Huang, Ying]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     ab31c7fd2d37bc3580d9d712d5f2dfb69901fca9
Gitweb:        https://git.kernel.org/tip/ab31c7fd2d37bc3580d9d712d5f2dfb69901fca9
Author:        Huang, Ying <ying.huang@xxxxxxxxx>
AuthorDate:    Tue, 22 Mar 2022 08:39:22 +01:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 22 Mar 2022 08:49:22 +01:00

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@xxxxxxxxxxx>
Tested-by: Qian Cai <quic_qiancai@xxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 89d21fd..ee0664c 100644
--- 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;