[SRU P][PATCH 0/1] Fix netdevsim crashing in nl_netdev test

[Stefan Bader]

BugLink: https://bugs.launchpad.net/bugs/2121866

[SRU Justification]

== Impact ==
Since SRU cycle 2025.08.11 we saw the ubuntu_kselftest_net suite failing
more or less harshly. The reason was that running nl_netdev.py was
causing a crash:

[ 5769.558910] RIP: 0010:mutex_lock+0x1c/0x50
[ 5769.568304] napi_disable+0x1d/0x50
[ 5769.568661] nsim_queue_stop+0x27/0x80 [netdevsim]
[ 5769.569140] netdev_rx_queue_restart+0x14a/0x260
[ 5769.569603] nsim_qreset_write+0x10d/0x150 [netdevsim]
[ 5769.570113] full_proxy_write+0x5e/0xa0
[ 5769.570499] vfs_write+0x10a/0x460

== Fix ==
It was found that this got introduced by
 "netdevsim: allow normal queue reset while down"
Apparently it should be allowed but stopping and starting the queue(s)
is not allowed while a device is not running.
This was handled with the following upstream change:
 net: devmem: don't call queue stop / start when the interface is down
However the submission was explicitly stating that is was not inteneded
as a bug fix but a clarification. Therefor it never was picked into
upstream stable.

== Testcase ==
Running ubuntu_kselftest_net (specifically nl_netdev.py) should no
longer fail and produce an oops.

== Regression Potential ==
Potentially the behaviour of netdev_queue_restart() (resetting network
devices) is impacted.

-Stefan


Jakub Kicinski (1):
  net: devmem: don't call queue stop / start when the interface is down

 include/net/netdev_queues.h |  4 ++++
 net/core/netdev_rx_queue.c  | 18 +++++++++++-------
 2 files changed, 15 insertions(+), 7 deletions(-)

-- 
2.43.0