Re: [PATCH v5] init: Disable defaults if init= fails

Frank Rowand
2014-10-01T00:41:18Z

The earliest mention I find of this on lkml is v4. Was there earlier
discussion of this elsewhere? (Just so I have a clue as to the full
context and don't repeat previous discussion.) The mention of names
in the change logs tells me I should be able to find the discussion
somewhere.

On 9/28/2014 7:40 PM, Andy Lutomirski wrote:
> If a user puts init=/whatever on the command line and /whatever
> can't be run, then the kernel will try a few default options before
> giving up. If init=/whatever came from a bootloader prompt, then
> this is unexpected but probably harmless. On the other hand, if it
> comes from a script (e.g. a tool like virtme or perhaps a future
> kselftest script), then the fallbacks are likely to exist, but
> they'll do the wrong thing. For example, they might unexpectedly
> invoke systemd.
>
> This makes a failure to run the specified init= process be fatal.
>
> As a temporary measure, users can set CONFIG_INIT_FALLBACK=y to
> preserve the old behavior. If no one speaks up, we can remove that
> option entirely after a release or two.

I'm speaking up already, no need to wait two releases. I like the
current behavior where I can fall back into a shell without
recompiling the kernel and/or changing the boot command line to
debug an init failure.

I would suggest that the current behavior remain the
default and the choice to make a failure of the specified
init= process fatal should be an explicit choice.

Instead of using a config option, would adding another kernel
command line option, such as 'init_fail_is_fatal', work for
your needs? I have a feeling this has already been proposed,
as the 'strictinit' option mentioned in the changes from v3
below might be the same concept?

Thanks,

Frank

>
> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
> ---
>
> Changes from v4:
> - Update the panic message (sorry for the noise)
>
> Changes from v3:
> - Get rid of the strictinit option. Now the new behavior is the default
> unless CONFIG_INIT_FALLBACK=y (Rob Landley)
>
> Changes from v2:
> - Improve docs further, to leave the door open to giving strictinit
> some sensible semantics if init= is not set.
> - Improve error output in the failure case (Shuah Khan).
>
> Changes from v1:
> - Add missing "if" to the docs (Randy Dunlap)
>
> init/Kconfig | 11 +++++++++++
> init/main.c | 7 ++++++-
> 2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index e84c6423a2e5..063029a1556f 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1299,6 +1299,17 @@ source "usr/Kconfig"
>
> endif
>
> +config INIT_FALLBACK
> + bool "Fall back to defaults if init= parameter is bad"
> + help
> + If enabled, the kernel will try the default init binaries if an
> + explicit request from the init= parameter fails.
> +
> + This is a temporary measure to allow broken configurations
> + to continue to boot.
> +
> + If unsure, say N.
> +
> config CC_OPTIMIZE_FOR_SIZE
> bool "Optimize for size"
> help
> diff --git a/init/main.c b/init/main.c
> index bb1aed928f21..2bd6105e5dc5 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -960,8 +960,13 @@ static int __ref kernel_init(void *unused)
> ret = run_init_process(execute_command);
> if (!ret)
> return 0;
> +#ifndef CONFIG_INIT_FALLBACK
> + panic("Requested init %s failed (error %d).",
> + execute_command, ret);
> +#else
> pr_err("Failed to execute %s (error %d). Attempting defaults...\n",
> - execute_command, ret);
> + execute_command, ret);
> +#endif
> }
> if (!try_to_run_init_process("/sbin/init") ||
> !try_to_run_init_process("/etc/init") ||
>