bpf: Free element after unlock in __htab_map_lookup_and_delete_elem()

bpf: Free element after unlock in __htab_map_lookup_and_delete_elem()

The freeing of special fields in map value may acquire a spin-lock
(e.g., the freeing of bpf_timer), however, the lookup_and_delete_elem
procedure has already held a raw-spin-lock, which violates the lockdep
rule.

The running context of __htab_map_lookup_and_delete_elem() has already
disabled the migration. Therefore, it is OK to invoke free_htab_elem()
after unlocking the bucket lock.

Fix the potential problem by freeing element after unlocking bucket lock
in __htab_map_lookup_and_delete_elem().

Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20250117101816.2101857-4-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>