Since running the 6.19 kernel package after a reboot (the previous boot was using 6.16, I think), putting the laptop to sleep would hang and eventually produce a kernel call trace. In the syslog, the first sign of the error is kernel: INFO: task kworker/u16:0:13041 blocked for more than 120 seconds. kernel: Tainted: G I 6.19.6+deb14-amd64 #1 Debian 6.19.6-1 (Syslog extract attached.) It never unblocks, and I have to reboot. Also the X screen is blank (with backlight), I guess because the laptop has halfway gone to sleep and is stuck there. I tried the 6.18 kernel package, which produced a similar problem: Putting the laptop to sleep also would hang, but in that case the syslog lists systemd-sleep as the blocked task. Until rebooting, which booted the 6.19 kernel, I have not had this problem. The previous working kernel was 6.16, I think. However, that boot had such a long uptime (months) that none of my rotated /var/log/syslog.n files show the boot (so I am not sure of the kernel version).
I've done more testing, and the problem now happens with all the kernel packages that I've tried: linux-image-6.12.63+deb13-amd64 linux-image-6.17.11+deb14-amd64 linux-image-6.18.5+deb14-amd64 linux-image-6.19.6+deb14-amd64 So, the problem is probably due to an upgrade to another package. One guess is systemd, because many of the error messages say that the hung process is systemd-sleep .
The following solution, or workaround, works for me (found on <https://bbs.archlinux.org/viewtopic.php?id=296954>). I made a file /etc/systemd/system/systemd-suspend.service.d/override.conf containing these two lines: [Service] Environment="SYSTEMD_SLEEP_FREEZE_USER_SESSIONS=false" (I did so via "systemctl edit systemd-suspend.service") Now suspend works reliably. Apparently this new behavior, of freezing the user slice, was introduced in systemd 256, so I must have been running an earlier version for a while. Anyway, now I am running systemd 260~rc4-1 (kernel 6.19.6+deb14-amd64). This solution was proposed first to solve suspend problems with properietary NVIDIA drivers. However, I had similar suspend problems without any proprietary drivers (the laptop uses intel graphics), and the same solution worked for me as for the NVIDIA users.