[Bug 880049] Re: 100% CPU usage in init if /dev/console is not available

[Torsten Knodt]

I would like to add something to the opinion that openvz should fix this.
I agree that it should be fixed by openvz.
But many people are not in control of the openvz/ Virtuozzo installation, because they just have rent a virtual server. And as it worked before it should still work because else those affected people don't trust into the dependability of Ubuntu any more. And by the way, there are many fixes for bad hardware in the kernel, why shouldn't there be fixes in Ubuntu for bad virtual hardware.

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Title:
  100% CPU usage in init if /dev/console is not available

Status in “upstart” package in Ubuntu:
  Confirmed

Bug description:
  When /dev/console is not available (for example when running as an OpenVZ guest), init consumes 100% time of one CPU core.
  Here is a strace excerpt captured on the OpenVZ host :

  ...
  waitid(P_ALL, 0, {}, WNOHANG|WEXITED|WSTOPPED|WCONTINUED, NULL) = 0
  clock_gettime(CLOCK_MONOTONIC, {3903451, 826182267}) = 0
  select(5, [0 3 4], [], [4], NULL) = 1 (in [0])
  read(0, "", 1) = 0
  waitid(P_ALL, 0, {}, WNOHANG|WEXITED|WSTOPPED|WCONTINUED, NULL) = 0
  clock_gettime(CLOCK_MONOTONIC, {3903451, 826467596}) = 0
  select(5, [0 3 4], [], [4], NULL) = 1 (in [0])
  read(0, "", 1) = 0
  waitid(P_ALL, 0, {}, WNOHANG|WEXITED|WSTOPPED|WCONTINUED, NULL) = 0
  clock_gettime(CLOCK_MONOTONIC, {3903451, 827157279}) = 0
  select(5, [0 3 4], [], [4], NULL) = 1 (in [0])
  read(0, "", 1) = 0
  ...

  Here is what happens :

  - in init's main function, system_setup_console(CONSOLE_OUTPUT) fails, leaving file descriptors 0 and 1 uninitialized
  - nih_main_loop_init eventually get called, initializing its interrupt_pipe on file descriptors 0 and 1
  - we end up calling system_setup_console(CONSOLE_NONE), resetting file descriptors 0 and 1 to /dev/null
  - in nih_main_loop, select is called on 0 (/dev/null instead of the pipe) which repeatedly appears to have changed

  I'm attaching a small patch which fixes this.

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