Comment 0 for bug 1978079

Systemd has a systemd-pstore component that scans the pstore on boot and if non-empty, takes all previously created dumps, transfers them into its journal and removes the pstore elements. This is very important on UEFI systems, which only have a limited amount of space for variables.

In Ubuntu, the kernel is configured with CONFIG_EFI_VARS_PSTORE=m which means the EFI pstore support gets loaded dynamically. In all of my boots, this dynamic module loading happened *after* systemd tried to check for pstore variables. So systemd-pstore never starts and never clears the UEFI variable store. I see this happening in AWS on Graviton instances, which eventually run out of space to store the dumps. On real hardware, this behavior may lead to unbootable systems.

```
$ systemctl status systemd-pstore
○ systemd-pstore.service - Platform Persistent Storage Archival
     Loaded: loaded (/lib/systemd/system/systemd-pstore.service; enabled; vendor preset: enabled)
     Active: inactive (dead)
  Condition: start condition failed at Thu 2022-06-09 09:11:41 UTC; 29min ago
             └─ ConditionDirectoryNotEmpty=/sys/fs/pstore was not met
       Docs: man:systemd-pstore(8)

Jun 09 09:11:41 ip-172-31-0-61 systemd[1]: Condition check resulted in Platform Persistent Storage Archival being skipped.

$ ls -la /sys/fs/pstore
total 0
drwxr-x--- 2 root root 0 Jun 9 09:11 .
drwxr-xr-x 8 root root 0 Jun 9 09:11 ..
-r--r--r-- 1 root root 1803 Jun 9 09:07 dmesg-efi-165476562001001
-r--r--r-- 1 root root 1777 Jun 9 09:07 dmesg-efi-165476562002001
-r--r--r-- 1 root root 1773 Jun 9 09:07 dmesg-efi-165476562003001
-r--r--r-- 1 root root 1815 Jun 9 09:07 dmesg-efi-165476562004001
-r--r--r-- 1 root root 1826 Jun 9 09:07 dmesg-efi-165476562005001
-r--r--r-- 1 root root 1754 Jun 9 09:07 dmesg-efi-165476562006001
-r--r--r-- 1 root root 1821 Jun 9 09:07 dmesg-efi-165476562007001
-r--r--r-- 1 root root 1767 Jun 9 09:07 dmesg-efi-165476562008001
-r--r--r-- 1 root root 1729 Jun 9 09:07 dmesg-efi-165476562009001
-r--r--r-- 1 root root 1819 Jun 9 09:07 dmesg-efi-165476562010001
-r--r--r-- 1 root root 1767 Jun 9 09:07 dmesg-efi-165476562011001
-r--r--r-- 1 root root 1775 Jun 9 09:07 dmesg-efi-165476562012001
-r--r--r-- 1 root root 1802 Jun 9 09:07 dmesg-efi-165476562013001
-r--r--r-- 1 root root 1812 Jun 9 09:07 dmesg-efi-165476562014001
-r--r--r-- 1 root root 1764 Jun 9 09:07 dmesg-efi-165476562015001
-r--r--r-- 1 root root 1795 Jun 9 09:11 dmesg-efi-165476589801001
-r--r--r-- 1 root root 1785 Jun 9 09:11 dmesg-efi-165476589802001
-r--r--r-- 1 root root 1683 Jun 9 09:11 dmesg-efi-165476589803001
-r--r--r-- 1 root root 1785 Jun 9 09:11 dmesg-efi-165476589804001
-r--r--r-- 1 root root 1771 Jun 9 09:11 dmesg-efi-165476589805001
-r--r--r-- 1 root root 1797 Jun 9 09:11 dmesg-efi-165476589806001
-r--r--r-- 1 root root 1805 Jun 9 09:11 dmesg-efi-165476589807001
-r--r--r-- 1 root root 1781 Jun 9 09:11 dmesg-efi-165476589808001
-r--r--r-- 1 root root 1806 Jun 9 09:11 dmesg-efi-165476589809001
-r--r--r-- 1 root root 1821 Jun 9 09:11 dmesg-efi-165476589810001
-r--r--r-- 1 root root 1763 Jun 9 09:11 dmesg-efi-165476589811001
-r--r--r-- 1 root root 1783 Jun 9 09:11 dmesg-efi-165476589812001
-r--r--r-- 1 root root 1788 Jun 9 09:11 dmesg-efi-165476589813001
-r--r--r-- 1 root root 1788 Jun 9 09:11 dmesg-efi-165476589814001
-r--r--r-- 1 root root 1786 Jun 9 09:11 dmesg-efi-165476589815001
```

This problem affects (at least) Ubuntu 20.04 and 22.04. A quick fix would be to configure CONFIG_EFI_VARS_PSTORE=y so that it's always available. A long term fix would make systemd rescan the directory after all module probing settled.