net: sched: tbf: fix the calculation of max_size

Current max_size is caluated from rate table. Now, the rate table
has been replaced and it's wrong to caculate max_size based on this
rate table. It can lead wrong calculation of max_size.

The burst in kernel may be lower than user asked, because burst may gets
some loss when transform it to buffer(E.g. "burst 40kb rate 30mbit/s")
and it seems we cannot avoid this loss. Burst's value(max_size) based on
rate table may be equal user asked. If a packet's length is max_size, this
packet will be stalled in tbf_dequeue() because its length is above the
burst in kernel so that it cannot get enough tokens. The max_size guards
against enqueuing packet sizes above q->buffer "time" in tbf_enqueue().

To make consistent with the calculation of tokens, this patch add a helper
psched_ns_t2l() to calculate burst(max_size) directly to fix this problem.

After this fix, we can support to using 64bit rates to calculate burst as well.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 70 insertions, 45 deletions

diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
index a6090051c5db..a44928c6ba24 100644
--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c
@@ -118,6 +118,30 @@ struct tbf_sched_data {
 };
 
 
+/* Time to Length, convert time in ns to length in bytes
+ * to determinate how many bytes can be sent in given time.
+ */
+static u64 psched_ns_t2l(const struct psched_ratecfg *r,
+                         u64 time_in_ns)
+{
+        /* The formula is :
+         * len = (time_in_ns * r->rate_bytes_ps) / NSEC_PER_SEC
+         */
+        u64 len = time_in_ns * r->rate_bytes_ps;
+
+        do_div(len, NSEC_PER_SEC);
+
+        if (unlikely(r->linklayer == TC_LINKLAYER_ATM))
+                len = (len / 53) * 48;
+
+        if (len > r->overhead)
+                len -= r->overhead;
+        else
+                len = 0;
+
+        return len;
+}
+
 /*
  * Return length of individual segments of a gso packet,
  * including all headers (MAC, IP, TCP/UDP)
@@ -289,10 +313,11 @@ static int tbf_change(struct Qdisc *sch, struct nlattr *opt)
         struct tbf_sched_data *q = qdisc_priv(sch);
         struct nlattr *tb[TCA_TBF_MAX + 1];
         struct tc_tbf_qopt *qopt;
-        struct qdisc_rate_table *rtab = NULL;
-        struct qdisc_rate_table *ptab = NULL;
         struct Qdisc *child = NULL;
-        int max_size, n;
+        struct psched_ratecfg rate;
+        struct psched_ratecfg peak;
+        u64 max_size;
+        s64 buffer, mtu;
         u64 rate64 = 0, prate64 = 0;
 
         err = nla_parse_nested(tb, TCA_TBF_MAX, opt, tbf_policy);
@@ -304,38 +329,13 @@ static int tbf_change(struct Qdisc *sch, struct nlattr *opt)
                 goto done;
 
         qopt = nla_data(tb[TCA_TBF_PARMS]);
-        rtab = qdisc_get_rtab(&qopt->rate, tb[TCA_TBF_RTAB]);
-        if (rtab == NULL)
-                goto done;
-
-        if (qopt->peakrate.rate) {
-                if (qopt->peakrate.rate > qopt->rate.rate)
-                        ptab = qdisc_get_rtab(&qopt->peakrate, tb[TCA_TBF_PTAB]);
-                if (ptab == NULL)
-                        goto done;
-        }
-
-        for (n = 0; n < 256; n++)
-                if (rtab->data[n] > qopt->buffer)
-                        break;
-        max_size = (n << qopt->rate.cell_log) - 1;
-        if (ptab) {
-                int size;
-
-                for (n = 0; n < 256; n++)
-                        if (ptab->data[n] > qopt->mtu)
-                                break;
-                size = (n << qopt->peakrate.cell_log) - 1;
-                if (size < max_size)
-                        max_size = size;
-        }
-        if (max_size < 0)
-                goto done;
+        if (qopt->rate.linklayer == TC_LINKLAYER_UNAWARE)
+                qdisc_put_rtab(qdisc_get_rtab(&qopt->rate,
+                                              tb[TCA_TBF_RTAB]));
 
-        if (max_size < psched_mtu(qdisc_dev(sch)))
-                pr_warn_ratelimited("sch_tbf: burst %u is lower than device %s mtu (%u) !\n",
-                                    max_size, qdisc_dev(sch)->name,
-                                    psched_mtu(qdisc_dev(sch)));
+        if (qopt->peakrate.linklayer == TC_LINKLAYER_UNAWARE)
+                        qdisc_put_rtab(qdisc_get_rtab(&qopt->peakrate,
+                                                      tb[TCA_TBF_PTAB]));
 
         if (q->qdisc != &noop_qdisc) {
                 err = fifo_set_limit(q->qdisc, qopt->limit);
@@ -349,6 +349,39 @@ static int tbf_change(struct Qdisc *sch, struct nlattr *opt)
                 }
         }
 
+        buffer = min_t(u64, PSCHED_TICKS2NS(qopt->buffer), ~0U);
+        mtu = min_t(u64, PSCHED_TICKS2NS(qopt->mtu), ~0U);
+
+        if (tb[TCA_TBF_RATE64])
+                rate64 = nla_get_u64(tb[TCA_TBF_RATE64]);
+        psched_ratecfg_precompute(&rate, &qopt->rate, rate64);
+
+        max_size = min_t(u64, psched_ns_t2l(&rate, buffer), ~0U);
+
+        if (qopt->peakrate.rate) {
+                if (tb[TCA_TBF_PRATE64])
+                        prate64 = nla_get_u64(tb[TCA_TBF_PRATE64]);
+                psched_ratecfg_precompute(&peak, &qopt->peakrate, prate64);
+                if (peak.rate_bytes_ps <= rate.rate_bytes_ps) {
+                        pr_warn_ratelimited("sch_tbf: peakrate %llu is lower than or equals to rate %llu !\n",
+                                            peak.rate_bytes_ps, rate.rate_bytes_ps);
+                        err = -EINVAL;
+                        goto done;
+                }
+
+                max_size = min_t(u64, max_size, psched_ns_t2l(&peak, mtu));
+        }
+
+        if (max_size < psched_mtu(qdisc_dev(sch)))
+                pr_warn_ratelimited("sch_tbf: burst %llu is lower than device %s mtu (%u) !\n",
+                                    max_size, qdisc_dev(sch)->name,
+                                    psched_mtu(qdisc_dev(sch)));
+
+        if (!max_size) {
+                err = -EINVAL;
+                goto done;
+        }
+
         sch_tree_lock(sch);
         if (child) {
                 qdisc_tree_decrease_qlen(q->qdisc, q->qdisc->q.qlen);
@@ -362,13 +395,9 @@ static int tbf_change(struct Qdisc *sch, struct nlattr *opt)
         q->tokens = q->buffer;
         q->ptokens = q->mtu;
 
-        if (tb[TCA_TBF_RATE64])
-                rate64 = nla_get_u64(tb[TCA_TBF_RATE64]);
-        psched_ratecfg_precompute(&q->rate, &rtab->rate, rate64);
-        if (ptab) {
-                if (tb[TCA_TBF_PRATE64])
-                        prate64 = nla_get_u64(tb[TCA_TBF_PRATE64]);
-                psched_ratecfg_precompute(&q->peak, &ptab->rate, prate64);
+        memcpy(&q->rate, &rate, sizeof(struct psched_ratecfg));
+        if (qopt->peakrate.rate) {
+                memcpy(&q->peak, &peak, sizeof(struct psched_ratecfg));
                 q->peak_present = true;
         } else {
                 q->peak_present = false;
@@ -377,10 +406,6 @@ static int tbf_change(struct Qdisc *sch, struct nlattr *opt)
         sch_tree_unlock(sch);
         err = 0;
 done:
-        if (rtab)
-                qdisc_put_rtab(rtab);
-        if (ptab)
-                qdisc_put_rtab(ptab);
         return err;
 }