sched_ext: Allow only user DSQs for scx_bpf_consume(), scx_bpf_dsq_nr_queued() and...

SCX_DSQ_GLOBAL is special in that it can't be used as a priority queue and
is consumed implicitly, but all BPF DSQ related kfuncs could be used on it.
SCX_DSQ_GLOBAL will be split per-node for scalability and those operations
won't make sense anymore. Disallow SCX_DSQ_GLOBAL on scx_bpf_consume(),
scx_bpf_dsq_nr_queued() and bpf_iter_scx_dsq_new(). This means that
SCX_DSQ_GLOBAL can only be used as a dispatch target from BPF schedulers.

With scx_flatcg, which was using SCX_DSQ_GLOBAL as the fallback DSQ,
updated, this shouldn't affect any schedulers.

This leaves find_dsq_for_dispatch() the only user of find_non_local_dsq().
Open code and remove find_non_local_dsq().

Signed-off-by: tejun heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index d74d1fe06999e680c814cc29c5893f7b70d03b00..ed2b914c42d15f118b6b896c780427ac7bbaeb59 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -1808,16 +1808,6 @@ static struct scx_dispatch_q *find_user_dsq(u64 dsq_id)
        return rhashtable_lookup_fast(&dsq_hash, &dsq_id, dsq_hash_params);
 }
 
-static struct scx_dispatch_q *find_non_local_dsq(u64 dsq_id)
-{
-       lockdep_assert(rcu_read_lock_any_held());
-
-       if (dsq_id == SCX_DSQ_GLOBAL)
-               return &scx_dsq_global;
-       else
-               return find_user_dsq(dsq_id);
-}
-
 static struct scx_dispatch_q *find_dsq_for_dispatch(struct rq *rq, u64 dsq_id,
                                                    struct task_struct *p)
 {
@@ -1835,7 +1825,11 @@ static struct scx_dispatch_q *find_dsq_for_dispatch(struct rq *rq, u64 dsq_id,
                return &cpu_rq(cpu)->scx.local_dsq;
        }
 
-       dsq = find_non_local_dsq(dsq_id);
+       if (dsq_id == SCX_DSQ_GLOBAL)
+               dsq = &scx_dsq_global;
+       else
+               dsq = find_user_dsq(dsq_id);
+
        if (unlikely(!dsq)) {
                scx_ops_error("non-existent DSQ 0x%llx for %s[%d]",
                              dsq_id, p->comm, p->pid);
@@ -6176,7 +6170,7 @@ __bpf_kfunc bool scx_bpf_consume(u64 dsq_id)
 
        flush_dispatch_buf(dspc->rq);
 
-       dsq = find_non_local_dsq(dsq_id);
+       dsq = find_user_dsq(dsq_id);
        if (unlikely(!dsq)) {
                scx_ops_error("invalid DSQ ID 0x%016llx", dsq_id);
                return false;
@@ -6497,7 +6491,7 @@ __bpf_kfunc s32 scx_bpf_dsq_nr_queued(u64 dsq_id)
                        goto out;
                }
        } else {
-               dsq = find_non_local_dsq(dsq_id);
+               dsq = find_user_dsq(dsq_id);
                if (dsq) {
                        ret = READ_ONCE(dsq->nr);
                        goto out;
@@ -6546,7 +6540,7 @@ __bpf_kfunc int bpf_iter_scx_dsq_new(struct bpf_iter_scx_dsq *it, u64 dsq_id,
        if (flags & ~__SCX_DSQ_ITER_USER_FLAGS)
                return -EINVAL;
 
-       kit->dsq = find_non_local_dsq(dsq_id);
+       kit->dsq = find_user_dsq(dsq_id);
        if (!kit->dsq)
                return -ENOENT;