net_sched: sch_fq_codel: implement lockless fq_codel_dump()

Instead of relying on RTNL, fq_codel_dump() can use READ_ONCE()
annotations, paired with WRITE_ONCE() ones in fq_codel_change().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index 79f9d6de6c852268fa293f8067d029d385b54976..4f908c11ba9528f8f9f3af6752ff10005d6f6511 100644 (file)
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -396,40 +396,49 @@ static int fq_codel_change(struct Qdisc *sch, struct nlattr *opt,
        if (tb[TCA_FQ_CODEL_TARGET]) {
                u64 target = nla_get_u32(tb[TCA_FQ_CODEL_TARGET]);
 
-               q->cparams.target = (target * NSEC_PER_USEC) >> CODEL_SHIFT;
+               WRITE_ONCE(q->cparams.target,
+                          (target * NSEC_PER_USEC) >> CODEL_SHIFT);
        }
 
        if (tb[TCA_FQ_CODEL_CE_THRESHOLD]) {
                u64 val = nla_get_u32(tb[TCA_FQ_CODEL_CE_THRESHOLD]);
 
-               q->cparams.ce_threshold = (val * NSEC_PER_USEC) >> CODEL_SHIFT;
+               WRITE_ONCE(q->cparams.ce_threshold,
+                          (val * NSEC_PER_USEC) >> CODEL_SHIFT);
        }
 
        if (tb[TCA_FQ_CODEL_CE_THRESHOLD_SELECTOR])
-               q->cparams.ce_threshold_selector = nla_get_u8(tb[TCA_FQ_CODEL_CE_THRESHOLD_SELECTOR]);
+               WRITE_ONCE(q->cparams.ce_threshold_selector,
+                          nla_get_u8(tb[TCA_FQ_CODEL_CE_THRESHOLD_SELECTOR]));
        if (tb[TCA_FQ_CODEL_CE_THRESHOLD_MASK])
-               q->cparams.ce_threshold_mask = nla_get_u8(tb[TCA_FQ_CODEL_CE_THRESHOLD_MASK]);
+               WRITE_ONCE(q->cparams.ce_threshold_mask,
+                          nla_get_u8(tb[TCA_FQ_CODEL_CE_THRESHOLD_MASK]));
 
        if (tb[TCA_FQ_CODEL_INTERVAL]) {
                u64 interval = nla_get_u32(tb[TCA_FQ_CODEL_INTERVAL]);
 
-               q->cparams.interval = (interval * NSEC_PER_USEC) >> CODEL_SHIFT;
+               WRITE_ONCE(q->cparams.interval,
+                          (interval * NSEC_PER_USEC) >> CODEL_SHIFT);
        }
 
        if (tb[TCA_FQ_CODEL_LIMIT])
-               sch->limit = nla_get_u32(tb[TCA_FQ_CODEL_LIMIT]);
+               WRITE_ONCE(sch->limit,
+                          nla_get_u32(tb[TCA_FQ_CODEL_LIMIT]));
 
        if (tb[TCA_FQ_CODEL_ECN])
-               q->cparams.ecn = !!nla_get_u32(tb[TCA_FQ_CODEL_ECN]);
+               WRITE_ONCE(q->cparams.ecn,
+                          !!nla_get_u32(tb[TCA_FQ_CODEL_ECN]));
 
        if (quantum)
-               q->quantum = quantum;
+               WRITE_ONCE(q->quantum, quantum);
 
        if (tb[TCA_FQ_CODEL_DROP_BATCH_SIZE])
-               q->drop_batch_size = max(1U, nla_get_u32(tb[TCA_FQ_CODEL_DROP_BATCH_SIZE]));
+               WRITE_ONCE(q->drop_batch_size,
+                          max(1U, nla_get_u32(tb[TCA_FQ_CODEL_DROP_BATCH_SIZE])));
 
        if (tb[TCA_FQ_CODEL_MEMORY_LIMIT])
-               q->memory_limit = min(1U << 31, nla_get_u32(tb[TCA_FQ_CODEL_MEMORY_LIMIT]));
+               WRITE_ONCE(q->memory_limit,
+                          min(1U << 31, nla_get_u32(tb[TCA_FQ_CODEL_MEMORY_LIMIT])));
 
        while (sch->q.qlen > sch->limit ||
               q->memory_usage > q->memory_limit) {
@@ -522,6 +531,7 @@ init_failure:
 static int fq_codel_dump(struct Qdisc *sch, struct sk_buff *skb)
 {
        struct fq_codel_sched_data *q = qdisc_priv(sch);
+       codel_time_t ce_threshold;
        struct nlattr *opts;
 
        opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
@@ -529,30 +539,33 @@ static int fq_codel_dump(struct Qdisc *sch, struct sk_buff *skb)
                goto nla_put_failure;
 
        if (nla_put_u32(skb, TCA_FQ_CODEL_TARGET,
-                       codel_time_to_us(q->cparams.target)) ||
+                       codel_time_to_us(READ_ONCE(q->cparams.target))) ||
            nla_put_u32(skb, TCA_FQ_CODEL_LIMIT,
-                       sch->limit) ||
+                       READ_ONCE(sch->limit)) ||
            nla_put_u32(skb, TCA_FQ_CODEL_INTERVAL,
-                       codel_time_to_us(q->cparams.interval)) ||
+                       codel_time_to_us(READ_ONCE(q->cparams.interval))) ||
            nla_put_u32(skb, TCA_FQ_CODEL_ECN,
-                       q->cparams.ecn) ||
+                       READ_ONCE(q->cparams.ecn)) ||
            nla_put_u32(skb, TCA_FQ_CODEL_QUANTUM,
-                       q->quantum) ||
+                       READ_ONCE(q->quantum)) ||
            nla_put_u32(skb, TCA_FQ_CODEL_DROP_BATCH_SIZE,
-                       q->drop_batch_size) ||
+                       READ_ONCE(q->drop_batch_size)) ||
            nla_put_u32(skb, TCA_FQ_CODEL_MEMORY_LIMIT,
-                       q->memory_limit) ||
+                       READ_ONCE(q->memory_limit)) ||
            nla_put_u32(skb, TCA_FQ_CODEL_FLOWS,
-                       q->flows_cnt))
+                       READ_ONCE(q->flows_cnt)))
                goto nla_put_failure;
 
-       if (q->cparams.ce_threshold != CODEL_DISABLED_THRESHOLD) {
+       ce_threshold = READ_ONCE(q->cparams.ce_threshold);
+       if (ce_threshold != CODEL_DISABLED_THRESHOLD) {
                if (nla_put_u32(skb, TCA_FQ_CODEL_CE_THRESHOLD,
-                               codel_time_to_us(q->cparams.ce_threshold)))
+                               codel_time_to_us(ce_threshold)))
                        goto nla_put_failure;
-               if (nla_put_u8(skb, TCA_FQ_CODEL_CE_THRESHOLD_SELECTOR, q->cparams.ce_threshold_selector))
+               if (nla_put_u8(skb, TCA_FQ_CODEL_CE_THRESHOLD_SELECTOR,
+                              READ_ONCE(q->cparams.ce_threshold_selector)))
                        goto nla_put_failure;
-               if (nla_put_u8(skb, TCA_FQ_CODEL_CE_THRESHOLD_MASK, q->cparams.ce_threshold_mask))
+               if (nla_put_u8(skb, TCA_FQ_CODEL_CE_THRESHOLD_MASK,
+                              READ_ONCE(q->cparams.ce_threshold_mask)))
                        goto nla_put_failure;
        }