compiled btrfs into kernel: even as root: could not get lock /var/lib/apt/lists/lock: Permission denied

Question

I have installed the latest raspbian on /dev/sda1, root filesystem is btrfs. So I had to recompile the kernel and compile the btrfs module into the kernel. For that, I used the latest raspberrypi/linux git (4.4.8), following exactly what was said here.

Now, everything seems to work, except for two things:

• it fails to run "Update UTMP about System Boot/Shutdown" during boot

• I cannot run any package manager, be it apt-get, dpkg, or aptitude. apt-get update just fails with

  E: Could not get lock /var/lib/apt/lists/lock - open (13: Permission denied)
  E: Unable to lock directory /var/lib/apt/lists/
  E: Could not get lock /var/lib/dpkg/lock - open (13: Permission denied)
  E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?
  

  which is the only output.

I did search the internet and read just about everything I could find. But almost all the answers talk about running as root. So, no:

• I did not forget sudo, I also tried logging in as root or doing sudo bash, but it all makes no difference.
• I deleted all the lock files under /var, no success.
• There are no other processes running. The lock files stay deleted until I execute apt-get update again, which recreates them and then it fails again :(

And I installed both, Ubuntu as well as Raspbian - same problem.

This has got to do with my kernel since everything else is unmodified. But I am lost now. How can I debug this problem? Which kernel config option did I forget or break?

I looked at the process with strace and got

open("/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_LARGEFILE|O_NOFOLLOW, 0640) = 4
fcntl64(4, F_SETFD, FD_CLOEXEC)
fcntl64(4, F_SETLK64, {type=F_WRLCK, whence=SEEK_SET, start=0, len=0}, 0x...) = -1 EACCESS (Permission denied)

The only thing I am wondering about is the fcntl64? Why 64?

Answer 1

Oh no! Days of debugging wasted, but I finally found it: I disabled CONFIG_FILE_LOCKING (Enable POSIX file locking API), an option you will only see if CONFIG_EXPERT is set (which I usually don't set, but the raspberry config has it). It is needed for any locking, not just NFS.