Hi mainteners, Given the observations, I feel it very likely being caused by misfiring of restore_backup_on_exit(), and looking around the source tree I found something suspicious:
In the commit 5dec0f2f9cd4d4dd0109c25cd2b399a780179020, | unix exec: avoid atexit handlers when child exits | Needed in buster to avoid problems with backup/restore in grub-install. exit()'s in grub-core/osdep/unix/exec.c:grub_util_exec_redirect_all() are all replaced with _exit(), but grub_util_exec_pipe() and grub_util_exec_pipe_stderr() are left as-is, having exit() right after execvp() which is same to grub_util_exec_redirect_all() before the patch. Is this correct? Sorry this is just a wild guess, I don't know if this actually can cause the simptom, nor if this path is actually run... Additional info: - GPT partitions are just FAT32 EFI system + ext4 single flat root, there's nothing else. - It's just a router, nothing fancy is installed. Yay sysvinit. - The kernel is built from debian linux-source-4.19 (currently at 4.19.171-2) -- everything built-in without modules, with a minor patch (pastebin.com/raw/ikQKniWK). --- because of the mentioned glitch, the official debian linux-image doesn't work very well. (sure it boots, it doesn't hang, but...) Thanks in advance,