NOHZ tick-stop error with ath10k SDIO

[Qais Yousef]

Hi Paul

On 08/18/21 08:43, Paul E. McKenney wrote:
> On Wed, Aug 18, 2021 at 12:18:25PM -0300, Fabio Estevam wrote:
> > Hi,
> > 
> > When launching the hostapd application on a i.MX7 based board with an
> > ath10k device connected via SDIO, the following "NOHZ tick-stop error"
> > messages are seen:
> > 
> > # hostapd /etc/wifi.conf
> > Configuration file: /etc/wifi.conf
> > wlan0: interface state UNINITIALIZED->COUNTRY_UPDATE
> > [   63.021149] NOHZ tick-stop error: Non-RCU local softirq work is
> > pending, handler #08!!!
> > Using interface wlan0 with hwaddr 00:1f:7b:31:04:a0 and ssid "thessid"
> > [   67.332470] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
> > wlan0: interface state COUNTRY_UPDATE->ENABLED
> > wlan0: AP-ENABLED
> > [   68.025845] NOHZ tick-stop error: Non-RCU local softirq work is
> > pending, handler #08!!!
> > [   69.025973] NOHZ tick-stop error: Non-RCU local softirq work is
> > pending, handler #08!!!
> > [   69.607432] cfg80211: failed to load regulatory.db
> > [   72.026748] NOHZ tick-stop error: Non-RCU local softirq work is
> > pending, handler #08!!!
> > [   73.027039] NOHZ tick-stop error: Non-RCU local softirq work is
> > pending, handler #08!!!
> > [   74.027159] NOHZ tick-stop error: Non-RCU local softirq work is
> > pending, handler #08!!!
> > [   75.027109] NOHZ tick-stop error: Non-RCU local softirq work is
> > pending, handler #08!!!
> > [   76.027461] NOHZ tick-stop error: Non-RCU local softirq work is
> > pending, handler #08!!!
> > [   77.027391] NOHZ tick-stop error: Non-RCU local softirq work is
> > pending, handler #08!!!
> > [   78.027560] NOHZ tick-stop error: Non-RCU local softirq work is
> > pending, handler #08!!!
> > 
> > This happens on all kernel versions from 5.10  to 5.13.
> > 
> > Any ideas on how to fix this problem?
> 
> I believe that you need this commit (and possibly some prerequsites):
> 
> 47c218dcae65 ("tick/sched: Prevent false positive softirq pending warnings on RT")
> 
> Adding Qais on CC for his thoughts.

Sorry for the late response. A combination of holidays and sickness kept me
away from email for a while.

I did see an issue on 5.10 recently but I was running android kernel. I thought
initially the problem is similar to the upstream one we were seeing on mainline
for a while in the past but it turned out a genuine bug due to a patch that
tries to 'fix' softirq interference with RT. Reverting that patch fixed the
issue for me. It turned out later that it was specific to the platform I was
running on and it's not reproducible by others on other platforms.

Upstream 5.10-LTS was fine for me.

HTH.

Thanks

--
Qais Yousef