scx_bpf_cid_override() currently updates the cid lookup tables as it
walks the user supplied mapping. If validation fails midway, earlier
entries may remain installed.

Split validation and table updates so a failed override leaves the
existing mapping unchanged.

Signed-off-by: zhidao su (Xiaomi) <soolaugust@gmail.com>
---
 kernel/sched/ext/cid.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/sched/ext/cid.c b/kernel/sched/ext/cid.c
index f31113b080e9..9e3a466f296f 100644
--- a/kernel/sched/ext/cid.c
+++ b/kernel/sched/ext/cid.c
@@ -329,6 +329,11 @@ __bpf_kfunc void scx_bpf_cid_override(const s32 *cpu_to_cid, u32 cpu_to_cid__sz,
 			scx_error(sch, "cid %d assigned to multiple cpus", c);
 			return;
 		}
+	}
+
+	for_each_possible_cpu(cpu) {
+		s32 c = cpu_to_cid[cpu];
+
 		scx_cpu_to_cid_tbl[cpu] = c;
 		scx_cid_to_cpu_tbl[c] = cpu;
 	}
-- 
2.43.0

Hello.

for-7.3 already does this. scx_bpf_cid_override() validates the whole
mapping first (cid_valid() and the duplicate check) and only writes
scx_cpu_to_cid_tbl/scx_cid_to_cpu_tbl in a second pass, so a failed
override leaves the tables untouched. It also kmemdup()s the input up
front to avoid a concurrent-mutation race.

The patch is against an older cid.c and no longer applies, so no respin
is needed.

Thanks.

-- 
tejun