Re: [net-next,v9,09/15] quic: add congestion control
From: Simon Horman <horms@kernel.org>
Date: 2026-02-05 11:55:42
Also in:
linux-cifs
This is an AI-generated review of your patch. The human sending this email has considered the AI review valid, or at least plausible. For local reproduction steps see https://netdev-ai.bots.linux.dev/ai-local.html --- quic: add congestion control This patch introduces quic_cong for RTT measurement and congestion control, implementing a state machine with slow start, congestion avoidance, and recovery phases using the New Reno algorithm.
quoted hunk ↗ jump to hunk
diff --git a/net/quic/cong.c b/net/quic/cong.c --- /dev/null +++ b/net/quic/cong.c
[ ... ]
+static int quic_cong_check_persistent_congestion(struct quic_cong *cong, u64 time)
+{
+ u32 ssthresh;
+
+ /* rfc9002#section-7.6.1:
+ * (smoothed_rtt + max(4*rttvar, kGranularity) + max_ack_delay) *
+ * kPersistentCongestionThreshold
+ */
+ ssthresh = cong->smoothed_rtt + max(4 * cong->rttvar, QUIC_KGRANULARITY);
+ ssthresh = (ssthresh + cong->max_ack_delay) * QUIC_KPERSISTENT_CONGESTION_THRESHOLD;
+ if (cong->time - time <= ssthresh)
+ return 0;[ ... ]
+/* rfc9002#section-5: Estimating the Round-Trip Time */
+void quic_cong_rtt_update(struct quic_cong *cong, u64 time, u32 ack_delay)
+{
+ u32 adjusted_rtt, rttvar_sample;
+
+ /* Ignore RTT sample if ACK delay is suspiciously large. */
+ if (ack_delay > cong->max_ack_delay * 2)
+ return;
+
+ /* rfc9002#section-5.1: latest_rtt = ack_time - send_time_of_largest_acked */
+ cong->latest_rtt = cong->time - time;The field cong->time is described as "Cached current timestamp" in struct quic_cong, but where is it written? The socket struct is zero-initialized, so cong->time will always be 0. When computing RTT with a positive packet send timestamp in the time parameter, does this cause unsigned integer underflow? For example, if the packet was sent at time 12345, computing 0 - 12345 wraps to a very large value. The same issue appears in quic_cong_check_persistent_congestion() where cong->time - time is compared against ssthresh, and in quic_reno_on_packet_lost() and quic_reno_on_process_ecn() where recovery_time is set to cong->time.