Please apply 13221be72034 ("wifi: rtw88: Handle C2H_ADAPTIVITY in rtw_fw_c2h_cmd_handle()") to 6.6.y and 6.12.y

Please apply 13221be72034 ("wifi: rtw88: Handle C2H_ADAPTIVITY in rtw_fw_c2h_cmd_handle()") to 6.6.y and 6.12.y

[Mehmet Fide]

Hi,

please consider

  13221be72034 ("wifi: rtw88: Handle C2H_ADAPTIVITY in rtw_fw_c2h_cmd_handle()")

for the 6.6.y and 6.12.y stable trees. It is in mainline since 6.14 and
applies cleanly to both.

Without it rtw_fw_adaptivity_result() runs from the USB RX work: it
reads three registers as arguments of rtw_dbg(), which is an empty
inline when CONFIG_RTW88_DEBUG is off, so the reads still happen there.
Over USB a register read sleeps. On 6.12.112 with an RTL8822CU, the
only rtw88 chip with adaptivity support, this gave "Voluntary context
switch within RCU read-side critical section" in rtw_usb_rx_handler()
-> rtw_fw_c2h_cmd_rx_irqsafe() -> rtw_usb_read32() within a minute of
starting an AP, followed by "xHCI host controller not responding,
assume dead", which took every USB device on the board with it. With
the commit applied the same board ran the AP through a channel switch
test session without a message.

Thanks,
Mehmet

Re: Please apply 13221be72034 ("wifi: rtw88: Handle C2H_ADAPTIVITY in rtw_fw_c2h_cmd_handle()") to 6.6.y and 6.12.y

[Sasha Levin]

> Over USB a register read sleeps. On 6.12.112 with an RTL8822CU, the
> only rtw88 chip with adaptivity support, this gave "Voluntary context
> switch within RCU read-side critical section" in rtw_usb_rx_handler()

13221be72034 ("wifi: rtw88: Handle C2H_ADAPTIVITY in rtw_fw_c2h_cmd_handle()")
only prepares for the WQ_BH conversion in 3e3aa566dd18 ("wifi: rtw88: usb:
Preallocate and reuse the RX skbs"), which is in neither 6.12 nor 6.6. Stock
6.12.y and 6.6.y run rtw_usb_rx_handler() from a plain
create_singlethread_workqueue(), where a register read may sleep, so that splat
cannot come from an unmodified
6.12.112.

Could you send the full trace, and say whether your kernel carries that
conversion or other local rtw88 changes? We will take the patch if it
reproduces on unmodified stable.

-- 
Thanks,
Sasha

Re: Please apply 13221be72034 ("wifi: rtw88: Handle C2H_ADAPTIVITY in rtw_fw_c2h_cmd_handle()") to 6.6.y and 6.12.y

[Mehmet Fide]

Hi Sasha,

On 2026-10-06 Sasha Levin wrote:
> Could you send the full trace, and say whether your kernel carries that
> conversion or other local rtw88 changes? We will take the patch if it
> reproduces on unmodified stable.

You are right, and sorry for the noise: our 6.12 tree carries a backport
of 3e3aa566dd18 ("wifi: rtw88: usb: Preallocate and reuse the RX skbs"),
so the RX work runs on a BH workqueue there. The splat is the missing
follow-up to our own backport, not a problem of stock 6.12.y or 6.6.y.
Please drop the request.

Thanks,
Mehmet