[PATCH 1/3] net: dsa: sja1105: remove use of iterator after list_for_each_entry() loop

[Vladimir Oltean]

Jakob Koschel explains in the link below that there is a desire to
syntactically change list_for_each_entry() and list_for_each() such that
it becomes impossible to use the iterator variable outside the scope of
the loop.

Although sja1105_insert_gate_entry() makes legitimate use of the
iterator pointer when it breaks out, the pattern it uses may become
illegal, so it needs to change.

It is deemed acceptable to use a copy of the loop iterator, and
sja1105_insert_gate_entry() only needs to know the list_head element
before which the list insertion should be made. So let's profit from the
occasion and refactor the list iteration to a dedicated function.

An additional benefit is given by the fact that with the helper function
in place, we no longer need to special-case the empty list, since it is
equivalent to not having found any gating entry larger than the
specified interval in the list. We just need to insert at the tail of
that list (list_add vs list_add_tail on an empty list does the same
thing).

Link: https://patchwork.kernel.org/project/netdevbpf/patch/20220407102900.3086255-3-jakobkoschel@xxxxxxxxx/#24810127
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
---
 drivers/net/dsa/sja1105/sja1105_vl.c | 46 ++++++++++++++++++----------
 1 file changed, 29 insertions(+), 17 deletions(-)

diff --git a/drivers/net/dsa/sja1105/sja1105_vl.c b/drivers/net/dsa/sja1105/sja1105_vl.c
index b7e95d60a6e4..369be2ac3587 100644
--- a/drivers/net/dsa/sja1105/sja1105_vl.c
+++ b/drivers/net/dsa/sja1105/sja1105_vl.c
@@ -7,6 +7,27 @@
 
 #define SJA1105_SIZE_VL_STATUS			8
 
+static struct list_head *
+sja1105_first_entry_longer_than(struct list_head *entries,
+				s64 interval,
+				struct netlink_ext_ack *extack)
+{
+	struct sja1105_gate_entry *p;
+
+	list_for_each_entry(p, entries, list) {
+		if (p->interval == interval) {
+			NL_SET_ERR_MSG_MOD(extack, "Gate conflict");
+			return ERR_PTR(-EBUSY);
+		}
+
+		if (interval < p->interval)
+			return &p->list;
+	}
+
+	/* Empty list, or specified interval is largest within the list */
+	return entries;
+}
+
 /* Insert into the global gate list, sorted by gate action time. */
 static int sja1105_insert_gate_entry(struct sja1105_gating_config *gating_cfg,
 				     struct sja1105_rule *rule,
@@ -14,6 +35,7 @@ static int sja1105_insert_gate_entry(struct sja1105_gating_config *gating_cfg,
 				     struct netlink_ext_ack *extack)
 {
 	struct sja1105_gate_entry *e;
+	struct list_head *pos;
 	int rc;
 
 	e = kzalloc(sizeof(*e), GFP_KERNEL);
@@ -24,25 +46,15 @@ static int sja1105_insert_gate_entry(struct sja1105_gating_config *gating_cfg,
 	e->gate_state = gate_state;
 	e->interval = entry_time;
 
-	if (list_empty(&gating_cfg->entries)) {
-		list_add(&e->list, &gating_cfg->entries);
-	} else {
-		struct sja1105_gate_entry *p;
-
-		list_for_each_entry(p, &gating_cfg->entries, list) {
-			if (p->interval == e->interval) {
-				NL_SET_ERR_MSG_MOD(extack,
-						   "Gate conflict");
-				rc = -EBUSY;
-				goto err;
-			}
-
-			if (e->interval < p->interval)
-				break;
-		}
-		list_add(&e->list, p->list.prev);
+	pos = sja1105_first_entry_longer_than(&gating_cfg->entries,
+					      e->interval, extack);
+	if (IS_ERR(pos)) {
+		rc = PTR_ERR(pos);
+		goto err;
 	}
 
+	list_add(&e->list, pos->prev);
+
 	gating_cfg->num_entries++;
 
 	return 0;
-- 
2.25.1