[PATCH net v2 0/2] net: usb: cdc_ncm/cdc_mbim: fix netpoll lockup in tx_fixup

[Nicolai Buchwitz]

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@xxxxxxxxxxx

Signed-off-by: Nicolai Buchwitz <nb@xxxxxxxxxxx>
---
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@xxxxxxxxxxx>