net/sched: taprio: prepare taprio_dump() for RTNL removal

We soon will no longer hold RTNL in qdisc dumps.

Add READ_ONCE()/WRITE_ONCE() annotations.

Note: taprio already uses RCU to protect most of its fields.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260501064247.2027688-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 45245157e00a69311304f8c69f9ee9d80bc4f4d8..71b690e1974dad8fbab7e12998e03f86a0847a98 100644 (file)
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -308,10 +308,10 @@ static void taprio_update_queue_max_sdu(struct taprio_sched *q,
 
                if (max_sdu != U32_MAX) {
                        sched->max_frm_len[tc] = max_sdu + dev->hard_header_len;
-                       sched->max_sdu[tc] = max_sdu;
+                       WRITE_ONCE(sched->max_sdu[tc], max_sdu);
                } else {
                        sched->max_frm_len[tc] = U32_MAX; /* never oversized */
-                       sched->max_sdu[tc] = 0;
+                       WRITE_ONCE(sched->max_sdu[tc], 0);
                }
        }
 }
@@ -1771,8 +1771,8 @@ static int taprio_parse_tc_entries(struct Qdisc *sch,
        }
 
        for (tc = 0; tc < TC_QOPT_MAX_QUEUE; tc++) {
-               q->max_sdu[tc] = max_sdu[tc];
-               q->fp[tc] = fp[tc];
+               WRITE_ONCE(q->max_sdu[tc], max_sdu[tc]);
+               WRITE_ONCE(q->fp[tc], fp[tc]);
                if (fp[tc] != TC_FP_EXPRESS)
                        have_preemption = true;
        }
@@ -1852,12 +1852,14 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
                return -EINVAL;
        }
 
-       if (q->flags != TAPRIO_FLAGS_INVALID && q->flags != taprio_flags) {
-               NL_SET_ERR_MSG_MOD(extack,
-                                  "Changing 'flags' of a running schedule is not supported");
-               return -EOPNOTSUPP;
+       if (q->flags != taprio_flags) {
+               if (q->flags != TAPRIO_FLAGS_INVALID) {
+                       NL_SET_ERR_MSG_MOD(extack,
+                                          "Changing 'flags' of a running schedule is not supported");
+                       return -EOPNOTSUPP;
+               }
+               WRITE_ONCE(q->flags, taprio_flags);
        }
-       q->flags = taprio_flags;
 
        /* Needed for length_to_duration() during netlink attribute parsing */
        taprio_set_picos_per_byte(dev, q, extack);
@@ -1940,7 +1942,8 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
                        goto unlock;
                }
 
-               q->txtime_delay = nla_get_u32(tb[TCA_TAPRIO_ATTR_TXTIME_DELAY]);
+               WRITE_ONCE(q->txtime_delay,
+                          nla_get_u32(tb[TCA_TAPRIO_ATTR_TXTIME_DELAY]));
        }
 
        if (!TXTIME_ASSIST_IS_ENABLED(q->flags) &&
@@ -2283,8 +2286,8 @@ error_nest:
 }
 
 static int taprio_dump_tc_entries(struct sk_buff *skb,
-                                 struct taprio_sched *q,
-                                 struct sched_gate_list *sched)
+                                 const struct taprio_sched *q,
+                                 const struct sched_gate_list *sched)
 {
        struct nlattr *n;
        int tc;
@@ -2298,10 +2301,11 @@ static int taprio_dump_tc_entries(struct sk_buff *skb,
                        goto nla_put_failure;
 
                if (nla_put_u32(skb, TCA_TAPRIO_TC_ENTRY_MAX_SDU,
-                               sched->max_sdu[tc]))
+                               READ_ONCE(sched->max_sdu[tc])))
                        goto nla_put_failure;
 
-               if (nla_put_u32(skb, TCA_TAPRIO_TC_ENTRY_FP, q->fp[tc]))
+               if (nla_put_u32(skb, TCA_TAPRIO_TC_ENTRY_FP,
+                               READ_ONCE(q->fp[tc])))
                        goto nla_put_failure;
 
                nla_nest_end(skb, n);
@@ -2387,6 +2391,7 @@ static int taprio_dump(struct Qdisc *sch, struct sk_buff *skb)
        struct sched_gate_list *oper, *admin;
        struct tc_mqprio_qopt opt = { 0 };
        struct nlattr *nest, *sched_nest;
+       u32 txtime_delay;
 
        mqprio_qopt_reconstruct(dev, &opt);
 
@@ -2404,14 +2409,15 @@ static int taprio_dump(struct Qdisc *sch, struct sk_buff *skb)
        if (q->flags && nla_put_u32(skb, TCA_TAPRIO_ATTR_FLAGS, q->flags))
                goto options_error;
 
-       if (q->txtime_delay &&
-           nla_put_u32(skb, TCA_TAPRIO_ATTR_TXTIME_DELAY, q->txtime_delay))
+       txtime_delay = READ_ONCE(q->txtime_delay);
+       if (txtime_delay &&
+           nla_put_u32(skb, TCA_TAPRIO_ATTR_TXTIME_DELAY, txtime_delay))
                goto options_error;
 
        rcu_read_lock();
 
-       oper = rtnl_dereference(q->oper_sched);
-       admin = rtnl_dereference(q->admin_sched);
+       oper = rcu_dereference(q->oper_sched);
+       admin = rcu_dereference(q->admin_sched);
 
        if (oper && taprio_dump_tc_entries(skb, q, oper))
                goto options_error_rcu;