sched_ext: create_dsq: Return -EEXIST on duplicate request

create_dsq and therefore the scx_bpf_create_dsq kfunc currently silently
ignore duplicate entries. As a sched_ext scheduler is creating each DSQ
for a different purpose this is surprising behaviour.

Replace rhashtable_insert_fast which ignores duplicates with
rhashtable_lookup_insert_fast that reports duplicates (though doesn't
return their value). The rest of the code is structured correctly and
this now returns -EEXIST.

Tested by adding an extra scx_bpf_create_dsq to scx_simple. Previously
this was ignored, now init fails with a -17 code. Also ran scx_lavd
which continued to work well.

Signed-off-by: Jake Hillion <jake@hillion.co.uk>
Acked-by: Andrea Righi <arighi@nvidia.com>
Fixes: f0e1a0643a59 ("sched_ext: Implement BPF extensible scheduler class")
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 21575d39c3762828d5b991360ea9cbf843d8a9fa..b47be2729ece1ae3dfbf7b673d3e5caa01bf77dc 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -4171,8 +4171,8 @@ static struct scx_dispatch_q *create_dsq(u64 dsq_id, int node)
 
        init_dsq(dsq, dsq_id);
 
-       ret = rhashtable_insert_fast(&dsq_hash, &dsq->hash_node,
-                                    dsq_hash_params);
+       ret = rhashtable_lookup_insert_fast(&dsq_hash, &dsq->hash_node,
+                                           dsq_hash_params);
        if (ret) {
                kfree(dsq);
                return ERR_PTR(ret);