Watchdog device always busy

Technical Support
, , ,
1

Hello!

I’m working with a imx8m-plus board with Torizon 5.5

I need to write an application that will use the /dev/watchdog device

But the application always fails to open the device, it says that the resource is busy. I’m trying to open it like this:

api_watchdog_fd = open(“/dev/watchdog”, O_RDWR);

This is the output from fuser:

sudo fuser -v /dev/watchdog
** USER PID ACCESS COMMAND**
/dev/watchdog: root 1 F… systemd

It looks like systemd is using the watchdog? That’s why my application can’t open the /dev/watchdog device?

I’ve googled around a bit and I’ve tried removing all the watchdog related entries from the /etc/systemd/system.conf file, and rebooting the board, but that had no effect.

This is the dmesg output related to watchdog:

dmesg | grep watchdog
[ 1.352157] imx2-wdt 30280000.watchdog: timeout 60 sec (nowayout=0)
[ 9.168780] systemd[1]: Hardware watchdog ‘imx2+ watchdog’, version 0
[ 9.168801] systemd[1]: Set hardware watchdog to 30s.

And the Torizon version:

uname -r
5.4.161-5.5.0-devel+git.bfe277fce128

Question is: how can I disable the watchdog from being used by another process, so my application can open it?

2

Greetings @jose_au_zone,

You are on the right track but the method is a bit different. We store our config files for systemd here:

sudo ls /usr/lib/systemd/system.conf.d
00-systemd-conf.conf  10-systemd-conf.conf

Inside the file 10-systemd-conf.conf is where we set the systemd-watchdog usage:

[Manager]
# Change CtrlAltDelBurstAction from default of `reboot-force` to `none`.
# Disable the immediate reboot which occurs when Ctrl+Alt+Del is pressed more
# than 7 times per 2s
# https://www.freedesktop.org/software/systemd/man/systemd.html#SIGINT
CtrlAltDelBurstAction=none
DefaultEnvironment="MACHINE=verdin-imx8mp"
RuntimeWatchdogSec=30s

Unfortunately this is in a read-only part of the filesystem so you can’t trivially modify this file to remove the RuntimeWatchdogSec=30s line. However you can create another similar file to overwrite this. Create the following file /etc/systemd/system.conf.d/10-systemd-conf.conf. As for the contents it’s the exact same as the first file minus the last line regarding the watchdog. This file in /etc should now overwrite the one in /usr/lib. After a quick reboot you should see that the watchdog is not used by systemd anymore:

verdin-imx8mp-06849059:~$ dmesg | grep watchdog
[    1.323643] imx2-wdt 30280000.watchdog: timeout 60 sec (nowayout=0)
verdin-imx8mp-06849059:~$ sudo fuser -v /dev/watchdog
verdin-imx8mp-06849059:~$

Please give this a try and see if you can now use the watchdog for your needs.

Best Regards,
Jeremias

3

Thanks Jeremias, it worked!

Now my application can open the watchdog file descriptor just fine

4

Glad to hear it worked. Just one more thing, this might be obvious but please exercise caution now that the watchdog isn’t being used to monitor the kernel/systemd.

Best Regards,
Jeremias

5

I have a follow up question now, I can create a new topic to ask this if it is better.

I want our Yocto build to add this file automatically.

Currently we are doing our modifications with a .bbappend file named “linux-toradex_%.bbappend” and all of our changes are being applied correctly

To add this file I added those lines to the bbappend:

SRC_URI += “file://10-systemd-conf.conf”

do_install_append() {

install -d ${D}${sysconfdir}/systemd/system.conf.d/

install -m 0755 ${WORKDIR}/10-systemd-conf.conf ${D}${sysconfdir}/systemd/system.conf.d/

}

FILES_${PN} += “${sysconfdir}/systemd/”
FILES_${PN} += “${sysconfdir}/systemd/system.conf.d”
FILES_${PN} += “${sysconfdir}/systemd/system.conf.d/10-systemd-conf.conf”

I`ve added the last 3 lines after googling one error that I was having, which is:

ERROR: linux-toradex-5.4.129+gitAUTOINC+6e59391f91_828ec42a6a-r0 do_package: QA Issue: linux-toradex: Files/directories were installed but not shipped in any package:
/etc/systemd
/etc/systemd/system.conf.d
/etc/systemd/system.conf.d/10-systemd-conf.conf

But even after adding that line the error persists. Do you have any guidance on how to properly do this?

Thanks

6

Wait you’re doing this all in an append file for the linux-toradex recipe? I’m not sure how well that would work to be honest.

For reference we add our 10-systemd-conf.conf file in this bbappend in our layer: meta-toradex-torizon/systemd-conf_%.bbappend at dunfell-5.x.y · toradex/meta-toradex-torizon · GitHub

Which is a bbappend to the original recipe here: systemd-conf_244.3.bb\systemd\recipes-core\meta - openembedded-core - OpenEmbedded Core layer

Perhaps you can try a new separate bbappend in your own layer modeling that.

As an alternative you can also add this file using torizoncore-builder and making an image with that. See this for reference: Capturing Changes in the Configuration of a Board on TorizonCore | Toradex Developer Center

Best Regards,
Jeremias

7

Thank you so much!

Creating another bbappend for the systemd-conf in our layer and just copying the relevant code there worked!

8

Glad it worked out!