[Bug 829980] Re: upstart-udev-bridge eats 100% cpu calling dbus_message_iter_append_basic()

[James Hunt]

I believe I now understand the problem. This has nothing to do with
Upstart - it's a kernel issue. Well, to be more precise, it's a problem
with the firmware on your batteries coupled with the kernel not sanity
checking device property values before handing them to userspace.

The file below in the kernel emits udev events on behalf of power
supplies and batteries:

    drivers/power/power_supply_sysfs.c

The expectation is that a "struct power_supply"'s 'properties' are
encoded in ASCII. But let's look at @smagoun's log...

$ grep "[^[:print:]]" udev_power_supply.txt|od -xc
0000000    4f50    4557    5f52    5553    5050    594c    4d5f    444f
          P   O   W   E   R   _   S   U   P   P   L   Y   _   M   O   D
0000020    4c45    4e5f    4d41    3d45    5341    424d    3130    6332
          E   L   _   N   A   M   E   =   A   S   M   B   0   1   2   c
0000040    1468    f401    0ae0    4f50    4557    5f52    5553    5050
          h 024 001 364 340  \n   P   O   W   E   R   _   S   U   P   P
0000060    594c    4d5f    4e41    4655    4341    5554    4552    3d52
          L   Y   _   M   A   N   U   F   A   C   T   U   R   E   R   =
0000100    654e    6577    5472    6365    1468    f401    0ae0    4f50
          N   e   w   e   r   T   e   c   h 024 001 364 340  \n   P   O
0000120    4557    5f52    5553    5050    594c    4d5f    444f    4c45
          W   E   R   _   S   U   P   P   L   Y   _   M   O   D   E   L
0000140    4e5f    4d41    3d45    5341    424d    3130    6332    1468
          _   N   A   M   E   =   A   S   M   B   0   1   2   c   h 024
0000160    f401    0ae0    4f50    4557    5f52    5553    5050    594c
        001 364 340  \n   P   O   W   E   R   _   S   U   P   P   L   Y
0000200    4d5f    4e41    4655    4341    5554    4552    3d52    654e
          _   M   A   N   U   F   A   C   T   U   R   E   R   =   N   e
0000220    6577    5472    6365    1468    f401    0ae0
          w   e   r   T   e   c   h 024 001 364 340  \n
0000234
$ 

What we *expect* to see for the first entry is:

    POWER_SUPPLY_MODEL_NAME=ASMB012ch\n

What we *actually* see is

   POWER_SUPPLY_MODEL_NAME=ASMB012ch<garbage>\n

Where <garbage> in this case is "024 001 364 340" which are extended /
non-printable characters. So this data gets sent across to userspace
where it is picked up by udevd which then hands it on to upstart-udev-
bridge. The bridge pulls apart the udev message and constructs an
upstart event, adding all udev properties to that events environment.
upstart_emit_event() does this by calling
dbus_message_iter_append_basic(), but then that call barfs since it
detects the non-printable characters. Since upstart wraps the call to
upstart_emit_event() in an NIH_MUST(), upstart_emit_event() will get
called forever until it succeeds (which it won't), thus maxing out your
CPU.

One possible (generic) fix would be for
lib/kobject_uevent.c:add_uevent_var() to remove all non-printable
characters from uevent variables to avoid causing problems in userspace.


** Changed in: upstart (Ubuntu)
       Status: Confirmed => Invalid

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https://bugs.launchpad.net/bugs/829980

Title:
  upstart-udev-bridge eats 100% cpu calling
  dbus_message_iter_append_basic()

Status in “linux” package in Ubuntu:
  Incomplete
Status in “upstart” package in Ubuntu:
  Invalid

Bug description:
  the segv was created by me sending a kill -11. but the 100% cpu is
  unbarable

  ProblemType: Crash
  DistroRelease: Ubuntu 11.10
  Package: upstart 1.3-0ubuntu6
  ProcVersionSignature: Ubuntu 3.0.0-8.11-generic 3.0.1
  Uname: Linux 3.0.0-8-generic x86_64
  NonfreeKernelModules: fglrx
  Architecture: amd64
  Date: Sat Aug 20 11:48:34 2011
  ExecutablePath: /sbin/upstart-udev-bridge
  InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Alpha amd64+mac (20110803.1)
  ProcCmdline: upstart-udev-bridge --daemon
  ProcEnviron: PATH=(custom, no user)
  Signal: 11
  SourcePackage: upstart
  StacktraceTop:
   ?? () from /lib/x86_64-linux-gnu/libc.so.6
   ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
   ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
   dbus_message_iter_append_basic () from /lib/x86_64-linux-gnu/libdbus-1.so.3
   ?? ()
  Title: upstart-udev-bridge crashed with SIGSEGV in dbus_message_iter_append_basic()
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups:

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