From: Nicolai Buchwitz <nb@tipi-net.de>
To: "Oliver Neukum" <oliver@neukum.org>,
"Andrew Lunn" <andrew+netdev@lunn.ch>,
"David S. Miller" <davem@davemloft.net>,
"Eric Dumazet" <edumazet@kernel.org>,
"Jakub Kicinski" <kuba@kernel.org>,
"Paolo Abeni" <pabeni@redhat.com>,
"Sjur Brændeland" <sjur.brandeland@stericsson.com>,
"Alexey Orishko" <alexey.orishko@gmail.com>,
"Bjørn Mork" <bjorn@mork.no>,
"Greg Suarez" <gsuarez@smithmicro.com>
Cc: Breno Leitao <leitao@debian.org>,
linux-usb@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, Nicolai Buchwitz <nb@tipi-net.de>,
Mikkel Eskildsen <mke@visotia.com>
Subject: [PATCH net v2 0/2] net: usb: cdc_ncm/cdc_mbim: fix netpoll lockup in tx_fixup
Date: Wed, 21 Oct 2026 09:56:17 +0200 [thread overview]
Message-ID: <20261021-cdc-ncm-netpoll-v2-0-8818965bbb69@tipi-net.de> (raw)
Mikkel reported lockups with netconsole on a cdc_ncm device. Further
analysis showed that netpoll calls ndo_start_xmit() with IRQs off but
BHs on while holding the txq lock, and the spin_unlock_bh() in the
tx_fixup paths runs pending softirqs. A transmit from one of them then
spins on that txq lock.
Patch 1 fixes cdc_ncm. Mikkel reproduced the lockup and tested the fix.
Patch 2 fixes the same code in cdc_mbim and is untested.
Changes in v2:
- Reverse xmas in patch 1
- Link to v1: https://lore.kernel.org/r/20261020-cdc-ncm-netpoll-v1-0-682184384b49@tipi-net.de
Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
---
Nicolai Buchwitz (2):
net: usb: cdc_ncm: don't enable BHs in tx_fixup under netpoll
net: usb: cdc_mbim: don't enable BHs in tx_fixup under netpoll
drivers/net/usb/cdc_mbim.c | 6 ++++--
drivers/net/usb/cdc_ncm.c | 10 +++++++---
2 files changed, 11 insertions(+), 5 deletions(-)
---
base-commit: 044ad3c90d9d2df2c5cb3325ae17b4e9603a311f
change-id: 20261020-cdc-ncm-netpoll-d7a7f69dd2cc
Best regards,
--
Nicolai Buchwitz <nb@tipi-net.de>
next reply other threads:[~2026-10-21 7:56 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-21 7:56 Nicolai Buchwitz [this message]
2026-10-21 7:56 ` [PATCH net v2 1/2] net: usb: cdc_ncm: don't enable BHs in tx_fixup under netpoll Nicolai Buchwitz
2026-10-22 12:58 ` Simon Horman
2026-10-21 7:56 ` [PATCH net v2 2/2] net: usb: cdc_mbim: " Nicolai Buchwitz
2026-10-22 12:58 ` Simon Horman
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