Bug#827077: linux: autofs mounts hang after real mount is unmounted

[Julian Andres Klode]

Control: reassign -1 systemd 230-1
Control: retitle -1 systemd: autofs mount hang in 230
Control: tag -1 patch fixed-upstream

On Mon, Jun 13, 2016 at 12:16:40AM +0200, Julian Andres Klode wrote:
> Control: found -1 4.5.5-1
> Control: retitle -1 linux: autofs mounts hang after real mount is unmounted
> 
> 
> On Sun, Jun 12, 2016 at 01:31:34AM +0200, Julian Andres Klode wrote:
> > Package: src:linux
> > Version: 4.6.1-1
> > Severity: normal
> > 
> > Hi, my system mounts /boot/efi using autofs, so it is automatically unmounted
> > after not being used (for safety reasons). The settings are (from /proc/mounts):
> > 
> > systemd-1 /boot/efi autofs rw,relatime,fd=29,pgrp=1,timeout=10,minproto=5,maxproto=5,direct,pipe_ino=10578 0 0
> > /dev/sdb1 /boot/efi vfat rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=utf8,shortname=mixed,errors=remount-ro 0 0
> > 
> > At first, accessing /boot works normally. But once /boot/efi (vfat) is unmounted, the automount
> > mount causes processes accessing it to hang (see the dmesg below). Even manually mounting the vfat
> > partition does not unhang those processes and new processes still hang.
> > 
> > This affects ls --color /boot for example, which just hangs when doing lstat("/boot/efi").
> > 
> > This works successfully in 4.5.5-1, and I have not seen the bug in 4.6.0-{rc7,trunk} (but I might
> > not have looked at /boot in those versions).
> 
> Hmm, I just reproduced it in 4.5.5-1. Unmounting the autofs thing makes things work
> again. I wonder what's really causing this.
> 
> It definitely used to work at some point. Maybe it's actually a systemd issue? I'm not
> exactly sure how autofs works and who actually mounts the vfat and hangs doing so
> (kernel or systemd?).

It's a bug in systemd 230. Arch applies the following commit to fix it:

  # automount: handle expire_tokens when the mount unit changes its state (#3434)
  0a62f81045dd810c8f1223cccbac4d706ea2cb45

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