sched/topology: Fix sched_numa_find_nth_cpu() in CPU-less case

[ Upstream commit 617f2c38cb5ce60226042081c09e2ee3a90d03f8 ]

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>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Yicong Yang <yangyicong@hisilicon.com>
Cc: Mel Gorman <mgorman@suse.de>
Link: https://lore.kernel.org/r/20230819141239.287290-4-yury.norov@gmail.com
Closes: https://lore.kernel.org/lkml/CAAH8bW8C5humYnfpW3y5ypwx0E-09A3QxFE1JFzR66v+mO4XfA@mail.gmail.com/T/
Closes: https://lore.kernel.org/lkml/ZMHSNQfv39HN068m@yury-ThinkPad/T/#mf6431cb0b7f6f05193c41adeee444bc95bf2b1c4
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 05a5bc6..423d089 100644 (file)
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2122,12 +2122,16 @@ 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;