Re: [PATCH -printk] printk, tracing: fix console tracepoint

From: Paul E. McKenney
Date: Tue Jul 12 2022 - 09:49:26 EST

On Tue, Jul 12, 2022 at 09:39:40AM -0400, Steven Rostedt wrote:
> On Tue, 12 Jul 2022 04:49:54 -0700
> "Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote:
> > > But a quick fix that stopped the bleeding and allowed printk() to
> > > progress would be useful in the short term, regardless of whether or
> > > not in the longer term it makes sense to make srcu_read_lock_trace()
> > > and srcu_read_unlock_trace() NMI-safe.
> >
> > Except that doesn't rcuidle && in_nmi() imply a misplaced trace event?
> >
> > Isn't it still the case that you are not supposed to have trace events
> > in NMI handlers before RCU is watching or after it is no longer watching,
> > just as for entry/exit code in general? Once in the body of the handler,
> > rcuidle should be false and all should be well.
> >
> > Or am I missing something here?
> I guess the question is, can we have printk() in such a place? Because this
> tracepoint is attached to printk and where ever printk is done so is this
> tracepoint.

As I understand it, code in such a place should be labeled noinstr.
Then the call to printk() would be complained about as an illegal
noinstr-to-non-noinstr call.

But where exactly is that printk()?

Thanx, Paul