Re: [PATCH] printk/tracing: Do not trace printk_nmi_enter()

[Steven Rostedt]

On Fri, 7 Sep 2018 17:35:38 +0900
Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> wrote:

> Should't printk_nmi_enter()/printk_nmi_exit() still be notrace?
> Like you and Steven said - it's still before ftrace_nmi_enter()
> and should be notrace regardless.

Correct. My patch fixes both issues.

The patch that Peter is posting is in case for some reason in the future
printk_nmi_enter/exit() do something with interrupts or locking.

And the printk_nmi_enter/exit() is placed where it is, in case for some
reason lockdep_off/on() does a printk.

The printk_nmi_enter/exit() and lockdep_off/on() are only changing
state variables. Neither of them should be traced by ftrace.

My patch solved the problem and was not just fixing a symptom.

It could have been solved either way, but as Petr said, the
printk_nmi_enter/exit() should have been notrace, because it was before
ftrace_nmi_enter/exit(). Lockdep actually found this bug because the
lockdep_on/off() was not first.

-- Steve