From: smallm@panix.com   
      
   Henrik Carlqvist  writes:   
      
   > On Tue, 27 Sep 2022 13:15:25 -0400, Mike Small wrote:   
   >>     1. create an ext4 fs   
   >>     2. mount it   
   >>     3. copy files to it   
   >>     4. unmount it   
   >>     5. remount it at a different point   
   >>     6. access copied files.   
   >>   
   >> This sequence sometimes fails at step 5 and rarely in step 6.  Typically   
   >> it does not fail. Could be a hardware error or something else (I'm   
   >> always looking for a new thing to blame udevd on, for instance), but it   
   >> sure would be nice (but not reassuring) if only a sync or two was what   
   >> was needed.   
   >   
   > Umount is supposed to sync the file system before unmounting and   
   > returning.   
   >   
   > As Bit Twister said, it might be a good idea to check the exit status of   
   > all the commands and especially the umount commoand. Also look for error   
   > messages from the commands and most of all, check for warnings and errors   
   > in the output from dmesg when something like this goes wrong.   
   >   
      
   Well, we checked at least for exit code 0 both on the cp and the umount,   
   e.g. umount X || die...   
      
   I'm looking more closely now, but getting dmesg output is tricky cause   
   it runs in an initramfs and reboots on the failure. Likely I'll have to   
   log debugging with dmesg, etc. Just trying to narrow now the steps to   
   reproduce.   
      
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