Re: [PATCH v20 net-next 1/6] sched: Struct definition and parsing of dualpi2 qdisc

On Sat, 21 Jun 2025 21:33:26 +0200 chia-yu.chang@nokia-bell-labs.com wrote:

+static struct netlink_range_validation dualpi2_alpha_beta_range = {

• .min = 1,
• .max = ALPHA_BETA_MAX,

+};

+static struct netlink_range_validation dualpi2_wc_range = {

• .min = 0,
• .max = MAX_WC,

+};

+static struct netlink_range_validation dualpi2_ecn_mask_range = {

• .min = TCA_DUALPI2_ECN_MASK_L4S_ECT,
• .max = TCA_DUALPI2_ECN_MASK_MAX,

+};

ranges which fit in s16 can be expressed directly with NLA_POLICY_RANGE(), you don't need the out-of-line struct.

+static const struct nla_policy dualpi2_policy[TCA_DUALPI2_MAX + 1] = {

• [TCA_DUALPI2_LIMIT] = NLA_POLICY_MIN(NLA_U32, 1),
• [TCA_DUALPI2_MEMORY_LIMIT] = NLA_POLICY_MIN(NLA_U32, 1),
• [TCA_DUALPI2_TARGET] = {.type = NLA_U32},

nit: spaces around {} brackets = { .type = NLA_U32 },

• [TCA_DUALPI2_TUPDATE] = NLA_POLICY_MIN(NLA_U32, 1),
• [TCA_DUALPI2_ALPHA] =

• NLA_POLICY_FULL_RANGE(NLA_U32, &dualpi2_alpha_beta_range),
  

• [TCA_DUALPI2_BETA] =

• NLA_POLICY_FULL_RANGE(NLA_U32, &dualpi2_alpha_beta_range),
  

• [TCA_DUALPI2_STEP_THRESH] = {.type = NLA_U32},
• [TCA_DUALPI2_STEP_PACKETS] = {.type = NLA_FLAG},
• [TCA_DUALPI2_MIN_QLEN_STEP] = {.type = NLA_U32},
• [TCA_DUALPI2_COUPLING] = NLA_POLICY_MIN(NLA_U8, 1),
• [TCA_DUALPI2_DROP_OVERLOAD] =

• NLA_POLICY_MAX(NLA_U8, TCA_DUALPI2_DROP_OVERLOAD_MAX),
  

• [TCA_DUALPI2_DROP_EARLY] =

• NLA_POLICY_MAX(NLA_U8, TCA_DUALPI2_DROP_EARLY_MAX),
  

• [TCA_DUALPI2_C_PROTECTION] =

• NLA_POLICY_FULL_RANGE(NLA_U8, &dualpi2_wc_range),
  

• [TCA_DUALPI2_ECN_MASK] =

• NLA_POLICY_FULL_RANGE(NLA_U8, &dualpi2_ecn_mask_range),
  

• [TCA_DUALPI2_SPLIT_GSO] =

• NLA_POLICY_MAX(NLA_U8, TCA_DUALPI2_SPLIT_GSO_MAX),
  

+};

+static int dualpi2_change(struct Qdisc *sch, struct nlattr *opt,

• 	  struct netlink_ext_ack *extack)
  

+{

• struct nlattr *tb[TCA_DUALPI2_MAX + 1];
• struct dualpi2_sched_data *q;
• int old_backlog;
• int old_qlen;
• int err;
• if (!opt)

should there be an extack message here?

• return -EINVAL;
  

• err = nla_parse_nested(tb, TCA_DUALPI2_MAX, opt, dualpi2_policy,

• 	       extack);
  

• if (err < 0)

• return err;
  

• q = qdisc_priv(sch);
• sch_tree_lock(sch);
• if (tb[TCA_DUALPI2_LIMIT]) {

• u32 limit = nla_get_u32(tb[TCA_DUALPI2_LIMIT]);
  

• WRITE_ONCE(sch->limit, limit);
  

• WRITE_ONCE(q->memory_limit, get_memory_limit(sch, limit));
  

• }
• if (tb[TCA_DUALPI2_MEMORY_LIMIT])

• WRITE_ONCE(q->memory_limit,
  

• 	   nla_get_u32(tb[TCA_DUALPI2_MEMORY_LIMIT]));
  

• if (tb[TCA_DUALPI2_TARGET]) {

• u64 target = nla_get_u32(tb[TCA_DUALPI2_TARGET]);
  

• WRITE_ONCE(q->pi2_target, target * NSEC_PER_USEC);
  

• }
• if (tb[TCA_DUALPI2_TUPDATE]) {

• u64 tupdate = nla_get_u32(tb[TCA_DUALPI2_TUPDATE]);
  

• WRITE_ONCE(q->pi2_tupdate, convert_us_to_nsec(tupdate));
  

• }
• if (tb[TCA_DUALPI2_ALPHA]) {

• u32 alpha = nla_get_u32(tb[TCA_DUALPI2_ALPHA]);
  

• WRITE_ONCE(q->pi2_alpha, dualpi2_scale_alpha_beta(alpha));
  

• }
• if (tb[TCA_DUALPI2_BETA]) {

• u32 beta = nla_get_u32(tb[TCA_DUALPI2_BETA]);
  

• WRITE_ONCE(q->pi2_beta, dualpi2_scale_alpha_beta(beta));
  

• }
• if (tb[TCA_DUALPI2_STEP_THRESH]) {

• u32 step_th = nla_get_u32(tb[TCA_DUALPI2_STEP_THRESH]);
  

• bool step_pkt = nla_get_flag(tb[TCA_DUALPI2_STEP_PACKETS]);
  

• WRITE_ONCE(q->step_in_packets, step_pkt);
  

• WRITE_ONCE(q->step_thresh,
  

• 	   step_pkt ? step_th : convert_us_to_nsec(step_th));
  

• }

I don't get the reason for all these WRITE_ONCE()s. You lock the qdisc to make modifications, right? And the block under which I'm responding is performing two dependent writes, one to ->step_in_packets and the other to ->step_thresh a change which is definitely not atomic..