Re: squashfs can starve/block apps

["Joakim Tjernlund (Nokia)" <joakim.tjernlund@nokia.com>]

On Thu, 2025-06-26 at 10:09 +0200, Joakim Tjernlund wrote:
> We have an app running on a squashfs RFS(XZ compressed) and a appfs also on squashfs.
> Whenever we validate an SW update image(stream a image.xz, uncompress it and on to /dev/null), 
> the apps are starved/blocked and make almost no progress, system time in top goes up to 99+%
> and the console also becomes unresponsive.
> 
> This feels like kernel is stuck/busy in a loop and does not let apps execute.
> 
> Kernel 5.15.185
> 
> Any ideas/pointers ?
> 
>  Jocke

This will reproduce the stuck behaviour we see:
 > cd /tmp (/tmp is an tmpfs)
 > wget https://fullImage.xz

So just downloading it to tmpfs will confuse squashfs, seems to
me that squashfs somehow see the xz compressed pages in page cache/VFS and
tried to do something with them.

kernel 51.15.185 (aarch64)
user space: ARM 32 bit with thumb