[PATCH 2/6] sched_ext: Make scx_bpf_cid_node() a benign lookup for invalid cids

[Tao Cui]

From: Tao Cui <cuitao@xxxxxxxxxx>

scx_bpf_cid_node() is documented to return NUMA_NO_NODE when @cid is
invalid or there is no scheduler. Its implementation goes through
scx_cid_to_cpu(), whose cid_valid() calls scx_error() on an invalid
value, so an invalid @cid does end at NUMA_NO_NODE, but only after
flagging the whole scheduler for exit.

Bounds-check @cid in the kfunc instead, keeping the documented benign
return and leaving the aborting validation to the paths whose contracts
call for it.

Fixes: 5cadf7545cc6 ("sched_ext: Add a CID NUMA node lookup kfunc")
Signed-off-by: Tao Cui <cuitao@xxxxxxxxxx>
---
 kernel/sched/ext/cid.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/sched/ext/cid.c b/kernel/sched/ext/cid.c
index 8e04a8494e11..b09b2c73ccec 100644
--- a/kernel/sched/ext/cid.c
+++ b/kernel/sched/ext/cid.c
@@ -690,6 +690,16 @@ __bpf_kfunc s32 scx_bpf_cid_node(s32 cid, const struct bpf_prog_aux *aux)
 	sch = scx_prog_sched(aux);
 	if (unlikely(!sch))
 		return NUMA_NO_NODE;
+
+	/*
+	 * Bounds-check @cid here rather than letting scx_cid_to_cpu() do it:
+	 * its cid_valid() aborts the scheduler on an invalid value, while
+	 * this kfunc is documented as a benign lookup that returns
+	 * NUMA_NO_NODE.
+	 */
+	if (cid < 0 || cid >= num_possible_cpus())
+		return NUMA_NO_NODE;
+
 	cpu = scx_cid_to_cpu(sch, cid);
 	return cpu < 0 ? NUMA_NO_NODE : cpu_to_node(cpu);
 }
-- 
2.53.0

base-commit: 5b740a72b55c4267ba4d8010f17dde26b26f52d3