"Dead loop on virtual device" error without softirq-BKL on PREEMPT_RT

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From: Bert Karwatzki

Date: Mon Feb 16 2026 - 08:51:13 EST

Starting with linux-6.18, I see the following log messages

2026-02-15T23:50:17.558716+01:00 [ T1559] Dead loop on virtual device wlp4s0, fix it urgently!
2026-02-15T23:50:17.558737+01:00 [ T1559] Dead loop on virtual device wlp4s0, fix it urgently!
[...]

regarding my wireless network device

04:00.0 Network controller [0280]: MEDIATEK Corp. MT7921K (RZ608) Wi-Fi 6E 80MHz [14c3:0608]

I bisected this (from v6.17 to v6.18) and got this as the first bad commit:
3253cb49cbad ("softirq: Allow to drop the softirq-BKL lock on PREEMPT_RT")

Using CONFIG_PREEMPT_RT_NEEDS_BH_LOCK=y in v6.18.10 fixes the issue.

Bert Karwatzki