bpf: Allow BPF stream kfuncs while holding a lock

The BPF stream kfuncs bpf_stream_vprintk and bpf_stream_print_stack
do not sleep and so are safe to call while holding a lock. Amend
the verifier to allow that.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260203180424.14057-4-emil@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: etsal

kernel/bpf/verifier.c

@@ -12455,6 +12455,8 @@ enum special_kfunc_type {
 	KF_bpf_arena_free_pages,
 	KF_bpf_arena_reserve_pages,
 	KF_bpf_session_is_return,
+	KF_bpf_stream_vprintk,
+	KF_bpf_stream_print_stack,
 };
 
 BTF_ID_LIST(special_kfunc_list)
@@ -12533,6 +12535,8 @@ BTF_ID(func, bpf_arena_alloc_pages)
 BTF_ID(func, bpf_arena_free_pages)
 BTF_ID(func, bpf_arena_reserve_pages)
 BTF_ID(func, bpf_session_is_return)
+BTF_ID(func, bpf_stream_vprintk)
+BTF_ID(func, bpf_stream_print_stack)
 
 static bool is_task_work_add_kfunc(u32 func_id)
 {
@@ -12977,10 +12981,17 @@ static bool is_bpf_arena_kfunc(u32 btf_id)
 	       btf_id == special_kfunc_list[KF_bpf_arena_reserve_pages];
 }
 
+static bool is_bpf_stream_kfunc(u32 btf_id)
+{
+	return btf_id == special_kfunc_list[KF_bpf_stream_vprintk] ||
+	       btf_id == special_kfunc_list[KF_bpf_stream_print_stack];
+}
+
 static bool kfunc_spin_allowed(u32 btf_id)
 {
 	return is_bpf_graph_api_kfunc(btf_id) || is_bpf_iter_num_api_kfunc(btf_id) ||
-	       is_bpf_res_spin_lock_kfunc(btf_id) || is_bpf_arena_kfunc(btf_id);
+	       is_bpf_res_spin_lock_kfunc(btf_id) || is_bpf_arena_kfunc(btf_id) ||
+	       is_bpf_stream_kfunc(btf_id);
 }
 
 static bool is_sync_callback_calling_kfunc(u32 btf_id)