[PATCH v2 3/6] sched: fix sched_numa_find_nth_cpu() in CPU-less case

Yury Norov
2023-08-19T14:12:55Z

When the node provided by user is CPU-less, corresponding record in
sched_domains_numa_masks is not set. Trying to dereference it in the
following code leads to kernel crash.

To avoid it, start searching from the nearest node with CPUs.

Fixes: cd7f55359c90 ("sched: add sched_numa_find_nth_cpu()")
Reported-by: Yicong Yang <yangyicong@hisilicon.com>
Closes: https://lore.kernel.org/lkml/CAAH8bW8C5humYnfpW3y5ypwx0E-09A3QxFE1JFzR66v+mO4XfA@mail.gmail.com/T/
Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/lkml/ZMHSNQfv39HN068m@yury-ThinkPad/T/#mf6431cb0b7f6f05193c41adeee444bc95bf2b1c4
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Yicong Yang <yangyicong@hisilicon.com>
---
kernel/sched/topology.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index d3a3b2646ec4..c6e89afa0d65 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2113,12 +2113,16 @@ static int hop_cmp(const void *a, const void *b)
*/
int sched_numa_find_nth_cpu(const struct cpumask *cpus, int cpu, int node)
{
- struct __cmp_key k = { .cpus = cpus, .node = node, .cpu = cpu };
+ struct __cmp_key k = { .cpus = cpus, .cpu = cpu };
struct cpumask ***hop_masks;
int hop, ret = nr_cpu_ids;

rcu_read_lock();

+ /* CPU-less node entries are uninitialized in sched_domains_numa_masks */
+ node = numa_nearest_node(node, N_CPU);
+ k.node = node;
+
k.masks = rcu_dereference(sched_domains_numa_masks);
if (!k.masks)
goto unlock;
--
2.39.2