From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout01.posteo.de (mout01.posteo.de [185.67.36.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 432CB2E8DEB for ; Fri, 14 Aug 2026 14:04:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.67.36.65 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786716246; cv=none; b=hh/zE7tCPnm7mMQ1D3VClKSKe2sPgsolW1dmhMSI7ot2dhTqWHbdxa3Kk0Dy0SMAz1ztwY4WmG1L0JMFlF+bwL2kra/XXuzNKSu83Fx0646+ot20tq8Wp+gbywYny0CKU7upCHDe6M4hfOBa6Xqq2zngQq5ELM0Sph0iYmQpVcg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786716246; c=relaxed/simple; bh=KoHa5GbljRRG3jbxDYQ1Ubn0KE6wGG4QtLRjUCmaO3I=; h=Date:From:To:Cc:Message-ID:Subject:MIME-Version:Content-Type; b=Ksl+VImtb5qMIKlW3kxHctHpHQCtyxOCGa5kC9lVaFZX4RSNzh5jCrFemZwpxqHdoy8Xklu3o6RopC6XvYfK/GEL50vADGsDxjMnTEbjb3feV0mq1fLVB1XAyalNTkl6ly3qzZnd+CbJ4cVNERfnqALJ4mH4mWTwvvCKv7KIF4Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=posteo.de; spf=pass smtp.mailfrom=posteo.de; dkim=pass (2048-bit key) header.d=posteo.de header.i=@posteo.de header.b=WiwFc1CX; arc=none smtp.client-ip=185.67.36.65 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=posteo.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=posteo.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=posteo.de header.i=@posteo.de header.b="WiwFc1CX" Received: from submission (posteo.de [185.67.36.169]) by mout01.posteo.de (Postfix) with ESMTPS id 10556240027 for ; Fri, 14 Aug 2026 16:04:02 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=posteo.de; s=1984.8680eb; t=1786716242; bh=KoHa5GbljRRG3jbxDYQ1Ubn0KE6wGG4QtLRjUCmaO3I=; h=Date:From:To:Cc:Message-ID:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:From; b=WiwFc1CXA23kStNwqTi6BMwx0J5rcgd35R4f1y0vSTVKXWChx9DDveQF2I78uSwq0 ewkFIuRShevzYRwKvq57/bK0Sxg1QGquMTJTkw2dF/mZmDvXgJ/K6VV8RPo5ErX02f uzMhNleBeR7M6rLkI3ZcpNJtH3T0CEwvox13lPxPJ3EPe4hG410zfYPhndOG2jFVay O7wmFSMK0tsQ3K3TiXRKgmAZ3KZB1Blszymgg7S5Ch0/thuDwx53OplLFCnxCYlr0S g8o1PIhXVT6/JVfI0kaI0c2qaIBA78tIbqZPQvhE3N+AEcH70wK9ZeGJ4Eyq2xc1cy 0/jQWbpcDPWEw== Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4hM3qj3lKkz9rxy; Fri, 14 Aug 2026 16:04:01 +0200 (CEST) Date: Fri, 14 Aug 2026 14:04:01 +0000 From: Jonas Hort To: regressions@lists.linux.dev Cc: linux-wireless@vger.kernel.org, lorenzo.bianconi83@gmail.com Message-ID: <066b30cc-a9e6-4aeb-964d-71551e8ea3ef@posteo.de> Subject: [REGRESSION] mt7925: MLO connectivity silently stalls with 6GHz link active Precedence: bulk X-Mailing-List: linux-wireless@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Correlation-ID: <066b30cc-a9e6-4aeb-964d-71551e8ea3ef@posteo.de> Filed as: https://bugzilla.kernel.org/show_bug.cgi?id=3D221884 Summary: WiFi 7 MLO (5GHz+6GHz) on MT7925 silently stops passing traffic after a few minutes, while the driver continues to report a fully healthy link. Root cause appears to be a stalled WFDMA0 TX hardware queue. Reproduced on both linux 7.1.8 (stable) and 7.2.0-rc7 (mainline pre-release), not fixed as of rc7. Disabling the 6GHz radio on the access point eliminates the freeze entirely in my testing. This is a regression: reported by multiple users on the CachyOS forum as broken starting with the 7.1.x kernel line; earlier kernels (6.18.x longterm) are reported to work fine. I have not yet performed a commit-level bisection but can if guided on the best approach given the AP-side 6GHz dependency. --- Detailed description --- Symptom: When connected via MLO (Multi-Link Operation, EHT/WiFi 7) with two active links - one on 5GHz and one on 6GHz - network traffic silently stops after a few minutes of normal use (web browsing, etc). The connection continues to show as healthy: - `iw link` / `iw station dump` report the connection as associated, =C2=A0 authenticated, good signal (-60 to -65 dBm), high negotiated =C2=A0 bitrate (800-1700 Mbit/s), 0 tx retries, 0 tx failed. - Nothing is logged to dmesg/journalctl at the time of the freeze. - Ping to the gateway shows 100% packet loss for several minutes, =C2=A0 until the connection eventually recovers on its own. I built a small watchdog script (ping-based failure detection + live kernel log monitoring) to catch the freeze automatically and sample mt76 debugfs state repeatedly across the event. This revealed the actual mechanism: `/sys/kernel/debug/ieee80211/phy0/mt76/xmit-queues` shows the WFDMA0 hardware TX queue's `tail` pointer completely frozen while `head` keeps advancing - i.e. packets keep getting enqueued but the firmware stops draining the queue. RX stops in the same instant (rx byte/packet counters in `iw station dump` freeze completely). No tx retries or tx failures are ever reported by the driver, so it does not appear to notice the stall itself. Example from one incident (kernel 7.2.0-rc7): =C2=A0 t+1s:=C2=A0 WFDMA0: queued=3D130 head=3D390 tail=3D260=C2=A0=C2=A0 r= x bytes=3D184791894 =C2=A0 t+9s:=C2=A0 WFDMA0: queued=3D148 head=3D408 tail=3D260=C2=A0=C2=A0 r= x bytes=3D184791894 (unchanged) `tail` never advances during the whole stall window while `head` keeps growing - the queue is being filled but never drained. Reproduced this exact signature four times total (twice on 7.1.8-1, twice on 7.2.0-rc7-1), always with MLO 5GHz+6GHz active, always within 3-5 minutes of normal use. 6GHz correlation: My MLO links are 5GHz (5180 MHz) + 6GHz (varies, e.g. 6135 MHz). Fully disabling the 6GHz radio on the access point (FritzBox 5690 Pro, FRITZ!OS 8.25 - not just client-side band restriction via NetworkManager, which does not reliably suppress the second MLO link) results in 30+ minutes of clean operation with no freeze. Re-enabling 6GHz reproduces the freeze again within minutes. Regression info: Multiple users on the CachyOS forum report this started with the 7.1.x kernel line; the previous longterm kernel (6.18.x) is reported to work fine by another user with different affected hardware (different AP). I have not personally tested 6.18.x myself, and have not performed a commit-level bisection yet - happy to do so if pointed toward the most likely area of the driver, given the AP-side 6GHz dependency makes a fully automated bisection awkward. Steps to reproduce: 1. Connect to an AP advertising WiFi 7 MLO with 5GHz+6GHz link =C2=A0=C2=A0 options, so the client negotiates both links. 2. Use the connection normally (web browsing is sufficient). 3. Within roughly 3-5 minutes, new connections start hanging; =C2=A0=C2=A0 existing traffic stops. 4. Check `iw link` - link still reports as connected/healthy. 5. Check `/sys/kernel/debug/ieee80211/phy*/mt76/xmit-queues` - =C2=A0=C2=A0 WFDMA0 tail pointer frozen while head continues to advance. Environment: - Kernel: linux-cachyos 7.1.8-1 and linux-cachyos-rc 7.2.0-rc7-1 =C2=A0 (CachyOS, near-vanilla Arch-based build) - cat /proc/version: =C2=A0 Linux version 7.2.0-rc7-1-cachyos-rc (linux-cachyos-rc@cachyos) =C2=A0 (clang version 22.1.8, LLD 22.1.8) #1 SMP PREEMPT_DYNAMIC =C2=A0 Mon, 10 Aug 2026 20:51:00 +0000 - Distribution: CachyOS - Architecture: x86_64 - Kernel tainted: no (/proc/sys/kernel/tainted =3D 0) - WiFi hardware: MediaTek MT7925 (mt7925e driver, mt76 core), =C2=A0 WM Firmware Build 20260605184805, ASIC revision 79250000 - Access point: AVM FritzBox 5690 Pro, FRITZ!OS 8.25 Related community discussion: https://discuss.cachyos.org/t/mt7925-wifi-7-mlo-breaks-connectivity-on-7-1-= x-mt76-regression/31972 (I am the thread starter; several other users report matching symptoms with different hardware/APs) Possibly related (different symptom, same 6GHz/MT7925 area, worth checking for a common root cause): Bug 221627 - MT7925E - System locks up with flashing caps lock (comment 1 there: "caused by switching between AP's with the same 6GHz wifi name") Attachments (will add to this ticket): - Full incident logs for all four reproductions (dmesg + journalctl =C2=A0 + mt76 debugfs time series across each freeze) - iw station dump / iw link output during freeze - Kernel .config Note: checked bug 220424 (mlo_sta_cmd/sta_cmd regression) before filing - different symptom (persistent near-zero throughput vs. our intermittent full stall with healthy link stats) and different root cause (broadcast wtbl hdr_trans_tlv handling). That fix landed in 6.16.6/6.17-rc5, well before the kernel versions tested here, so it is not the cause of this issue.