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

[Julian Andres Klode]

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?).

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