Pi 4 brcmfmac AP (2.4 GHz): firmware stops host TX after a client's mDNS burst. Flow control stuck in XOFF until the driver is reloaded

未關閉
  • 哪裡不對？
#7,723 2 則留言 0 個 reaction 已指派 0 人 在 GitHub 檢視

維護者通常 1 天內回覆

還沒有人認領這個 Issue。

評估

難度
4/5
預估耗時
3-5 天
新手友好度
43/100
Issue 類型
缺陷
描述清晰度
基本清楚
活躍度
活躍
技術堆疊
c, linux
領域
networking

研究方向

Start by reading the brcmfmac flow control and transmit paths, then look for existing handling of fc_xoff and fc_xon; the issue does not name specific source files or tests. Try to reproduce the stall with the described 2.4 GHz AP and multicast burst, and inspect the debugfs counters. Done means the AP continues transmitting after the burst and the counters recover without reloading the driver.

由索引模型根據 Issue 內容生成。

描述

Describe the bug

A Pi 4B runs a NetworkManager hotspot (AP mode, 2.4 GHz, band bg, channel auto → 6, IPv4 shared). When a Windows 11 client joins, data flows for about 2 s, and then the Pi stops sending data to the client. Beacons continue. The driver's debugfs counters show the firmware turned host TX off and never turned it back on:

  • fc_xoff > fc_xon
  • f2txdata stops increasing

After that, reconnects fail at the 4-way handshake. Later the AP stops beaconing entirely. Only reloading the driver recovers it (modprobe -r brcmfmac_cyw brcmfmac; modprobe brcmfmac). No firmware trap or "halted" message is logged. The only related kernel messages are brcmf_vif_set_mgmt_ie: vndr ie set error : -52.

Trigger
A tcpdump on wlan0 shows that the stall starts when the client sends a burst of about 900 mDNS multicast packets in about 3 s. The packets are Windows Delivery Optimization re-announcing 76 _dosvc._tcp.local service instances, each about 540 bytes, with 3 probes and 3 announcements over both IPv4 and IPv6. This is a client-side quirk, but it's valid traffic, and it permanently disables the AP.

Test results

Test Result
Same client, 2.4 GHz, channels 6 and 11, Wi-Fi power saving on or off stalls every time
One run recovered after a 6 s outage (fc_xon caught up), so the stall looks like a race
Same client, same burst, 5 GHz (channel 36) fc_xoff 4 = fc_xon 4, stable 3+ min
Same client, outgoing mDNS blocked on the client no burst, fc_xoff 0, stable 3+ min
Same client after a reboot (no burst) stable
Android phone (about 40 mDNS packets) fc_xoff 23 = fc_xon 23, stable 3+ min
AP isolation enabled still stalls
Firmware 7.45.265 (standard) and 7.45.241 (minimal) both stall
Kernel 6.12.62 and 6.18.50 both stall
Ruled out: power (throttled=0x0), SDIO errors, and RF interference (the stall is repeatable across channels). Our guess is that airtime at the 1 Mbps basic rate on 2.4 GHz pushes the firmware into a flow-control state it doesn't recover from. We haven't tried reproducing it with a synthetic multicast flood.
Steps to reproduce the behaviour
  1. Start a 2.4 GHz NetworkManager hotspot on the Pi 4.
  2. Connect a client that sends about 900 multicast packets of about 540 bytes within a few seconds after associating. A long-running Windows 11 PC with Delivery Optimization LAN sharing on does this.
  3. Watch /sys/kernel/debug/ieee80211/phy*/counters: fc_xoff goes above fc_xon and f2txdata freezes.
Device (s)

Raspberry Pi 4 Mod. B

System
  • Raspberry Pi OS Trixie (image 2025-12-04), full-upgraded 2026-10-27
  • Kernel 6.18.50 (also seen on 6.12.62)
  • firmware-brcm80211 20260519
  • Firmware: BCM4345/6 7.45.265 (28bca26 CY) FWID 01-b677b91b; also 7.45.241 (minimal)
  • wpasupplicant 2.10-24+rpt3, NetworkManager AP mode
Logs

System Information.txt

Additional context

Possible related to #7092

主要語言
C
星號
13.3k
分支
5.5k
平均合併
3 天 20 小時
30 天內合併 PR
27

環境準備

這個專案沒有提供開發容器、Dockerfile 或貢獻指南，環境需要你自己搭建：先看它的 README，通用步驟見我們的新手貢獻指南。

從這裡開始

  1. 先讀完整個 Issue，再讀專案的貢獻指南。
  2. 在 Issue 下留言說明你要接手 —— 這能避免兩個人做同樣的事。
  3. Fork 儲存庫，在一個分支上完成修改。
  4. 送出 Pull Request，並在描述裡引用這個 Issue 編號。

raspberrypi/linux 的其他 Issue

查看 raspberrypi/linux 的全部 Issue

相似的 Issue

更多 C Issue

把新 issue 寄到你的電子郵件信箱

精選適合新手參與的 GitHub issue 摘要。