[laptop-mode] [PATCH] Laptop mode hangs indefinately when battery polling is used

[Matthijs Kooijman]

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Hi,

I've encountered symptoms of the same issue reported a while back ("unable =
to
stop LM while on battery"), located the problem and found a fix for it.

The problem I was facing, was that laptop-mode sometimes hangs indefinately=
 on
startup. Initially I suspected a kernel upgrade, but it turns out the batte=
ry
polling module is responsible for this. Since the battery polling is not
started when on AC, and I usually boot on AC (and do dehibernation on the
road), I hadn't noticed this issue before.

What happens is actually really simple: /etc/init.d/laptopmode starts
laptop-mode, but captures its output like this:

  RESULT=3D`/usr/sbin/laptop_mode init auto`

Somewhere during it's run, laptop_mode calls
/usr/share/laptop-mode-tools/modules/battery-level-polling, which again cal=
ls
the lm-polling-daemon helper:
  /usr/share/laptop-mode-tools/module-helpers/lm-polling-daemon &

However, this daemon is just backgrounded with &, but it's stdout is still
connected, meaning that RESULT=3D`` line will wait for the polling daemon to
quit before returning (i.e., never). This was particularly nasty to find,
since the laptop_mode script itself of course continues as normal, all the =
way
to its end, and only then execution hangs.

To fix this, we should disconnect at least stdout from the polling daemon, =
but
disconnecting all file descriptors is probably better. e.g.:=20

  /usr/share/laptop-mode-tools/module-helpers/lm-polling-daemon \=20
  < /dev/null > /dev/null 2> /dev/null &

Also see the attached (trivial) patch, which fixes the issue. Since this is=
sue
can prevent systems from booting and shutting down, I hope this will be fix=
ed
soon!

Gr.

Matthijs

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