Re: [PATCH] printk: fix discarding message when recursion_bug

[Ingo Molnar <mingo@elte.hu>]

* Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com> wrote:

> Ingo Molnar wrote:
> > * Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com> wrote:
> > 
> >> From: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
> >>
> >> Impact: fix
> >>
> >> When recursion_bug is true, kernel discards original message because printk_buf
> >> contains recursion_bug_msg with NULL terminator. The sizeof(recursion_bug_msg)
> >> makes this, use strlen() to get correct length without NULL terminator.
> >>
> >> Reported-by: Toshikazu Nakayama <nakayama.ts@ncos.nec.co.jp>
> >> Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
> >> ---
> >>  kernel/printk.c |    2 +-
> >>  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > Good one - applied to tip/core/printk, thanks!
> > 
> > Btw., i'm curious: in what situation was such recursion observed, and how 
> > did the kernel behave? You saw a truncated recursion message in dmesg - or 
> > was it worse?
> 
> I'm not sure about the real situation. I've heard this issue was found 
> in printing messages in NMI handler, maybe with artificial kernel stuck.

yeah, accidental NMI recursion back into printk could indeed cause the 
recursion message to pop up.

	Ingo