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SubjectRe: [PATCH] If init dies, log a signal which killed it, if any.
On 01/20, Denys Vlasenko wrote:
>
> I just received another user's pleas for help when their
> init mystriously dies. I again explained that they need to check
> whether it dies because of bad instruction, a segv, or something else.
>
> Which prompted me to make kernel do this first step automatically.
> We can easily detect when the death is from e.g. SIGILL,
> and let user know that.
>
> The code is fairly self-explanatory. Compile-tested.
>
> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
> ---
> kernel/exit.c | 23 ++++++++++++++++++++++-
> 1 files changed, 22 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 294b170..89d0892 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -710,8 +710,29 @@ static struct task_struct *find_new_reaper(struct task_struct *father)
>
> if (unlikely(pid_ns->child_reaper == father)) {
> write_unlock_irq(&tasklist_lock);
> - if (unlikely(pid_ns == &init_pid_ns))
> + if (unlikely(pid_ns == &init_pid_ns)) {
> + /*
> + * The situation when init segfaults is rather typical.
> + * Give some useful diagnostics: do we die on signal?
> + */
> + if (fatal_signal_pending(father)) {

The fatal signal can be already dequeued. Although mostly this works.

> + const char *msg = "";
> + sigset_t *mask = &father->pending.signal;
> + /* Only force_sig()ned signals kill init */
> + if (sigismember(mask, SIGSEGV))
> + msg = " SIGSEGV";
> + if (sigismember(mask, SIGBUS))
> + msg = " SIGBUS";
> + if (sigismember(mask, SIGILL))
> + msg = " SIGILL";
> + if (sigismember(mask, SIGFPE))
> + msg = " SIGFPE";

This doesn't look right too. Again, if it was killed by SIGSEGV
this signal can be dequeued and not pending.

> + /* (do we want to check SIGTRAP too?) */
> + printk(KERN_ERR
> + "init received fatal signal%s\n", msg);
> + }

I'd suggest this trivial change instead,

- panic("Attempted to kill init!");
+ panic("Attempted to kill init! code=%08x\n",
+ father->signal->group_exit_code ?: father->exit_code);

Oleg.



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