bpf: net_sched: Fix using bpf qdisc as default qdisc

Use bpf_try_module_get()/bpf_module_put() instead of try_module_get()/
module_put() when handling default qdisc since users can assign a bpf
qdisc to it.

To trigger the bug:
$ bpftool struct_ops register bpf_qdisc_fq.bpf.o /sys/fs/bpf
$ echo bpf_fq > /proc/sys/net/core/default_qdisc

Fixes: c824034 ("bpf: net_sched: Support implementation of Qdisc_ops in bpf")
Signed-off-by: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250429192128.3860571-1-ameryhung@gmail.com

Author: ameryhung

net/sched/sch_api.c

@@ -208,7 +208,7 @@ static struct Qdisc_ops *qdisc_lookup_default(const char *name)
 
 	for (q = qdisc_base; q; q = q->next) {
 		if (!strcmp(name, q->id)) {
-			if (!try_module_get(q->owner))
+			if (!bpf_try_module_get(q, q->owner))
 				q = NULL;
 			break;
 		}
@@ -238,7 +238,7 @@ int qdisc_set_default(const char *name)
 
 	if (ops) {
 		/* Set new default */
-		module_put(default_qdisc_ops->owner);
+		bpf_module_put(default_qdisc_ops, default_qdisc_ops->owner);
 		default_qdisc_ops = ops;
 	}
 	write_unlock(&qdisc_mod_lock);

net/sched/sch_generic.c

@@ -1002,14 +1002,14 @@ struct Qdisc *qdisc_create_dflt(struct netdev_queue *dev_queue,
 {
 	struct Qdisc *sch;
 
-	if (!try_module_get(ops->owner)) {
+	if (!bpf_try_module_get(ops, ops->owner)) {
 		NL_SET_ERR_MSG(extack, "Failed to increase module reference counter");
 		return NULL;
 	}
 
 	sch = qdisc_alloc(dev_queue, ops, extack);
 	if (IS_ERR(sch)) {
-		module_put(ops->owner);
+		bpf_module_put(ops, ops->owner);
 		return NULL;
 	}
 	sch->parent = parentid;