Re: [PATCH v4 04/17] context_tracking: Add ct_state and CT_WARN_ON

Ingo Molnar
2015-06-30T12:54:00Z

* Borislav Petkov <bp@alien8.de> wrote:

> On Mon, Jun 29, 2015 at 12:33:36PM -0700, Andy Lutomirski wrote:
> > This will let us sprinkle sanity checks around the kernel without
> > making too much of a mess.
> >
> > Signed-off-by: Andy Lutomirski <luto@kernel.org>
> > ---
> > include/linux/context_tracking.h | 15 +++++++++++++++
> > include/linux/context_tracking_state.h | 1 +
> > 2 files changed, 16 insertions(+)
> >
> > diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
> > index b96bd299966f..008fc67d0d96 100644
> > --- a/include/linux/context_tracking.h
> > +++ b/include/linux/context_tracking.h
> > @@ -49,13 +49,28 @@ static inline void exception_exit(enum ctx_state prev_ctx)
> > }
> > }
> >
> > +
> > +/**
> > + * ct_state() - return the current context tracking state if known
> > + *
> > + * Returns the current cpu's context tracking state if context tracking
>
> CPU's
>
> > + * is enabled. If context tracking is disabled, returns
> > + * CONTEXT_DISABLED. This should be used primarily for debugging.
> > + */
> > +static inline enum ctx_state ct_state(void)
> > +{
> > + return context_tracking_is_enabled() ?
> > + this_cpu_read(context_tracking.state) : CONTEXT_DISABLED;
> > +}
> > #else
> > static inline void user_enter(void) { }
> > static inline void user_exit(void) { }
> > static inline enum ctx_state exception_enter(void) { return 0; }
> > static inline void exception_exit(enum ctx_state prev_ctx) { }
> > +static inline enum ctx_state ct_state(void) { return CONTEXT_DISABLED; }
> > #endif /* !CONFIG_CONTEXT_TRACKING */
> >
> > +#define CT_WARN_ON(cond) WARN_ON(context_tracking_is_enabled() && (cond))
>
> Btw, that "CT_" prefix makes this look like it is the software
> controlling this thing:
>
> https://upload.wikimedia.org/wikipedia/commons/thumb/2/27/UPMCEast_CTscan.jpg/1280px-UPMCEast_CTscan.jpg
>
> :-)
>
> Other kernel code uses "cxt" or "ctxt" abbreviations. Maybe
>
> CTXT_WARN_ON(cond)

So this really looks too much like 'TXT' - which is very far from what it tries to
express.

So we should either use a CTX_TRACK_ prefix that is unambiguous, or live with CT_
and its ambiguity. (There's another ambiguity it has: 'ct' stands for 'connection
tracking' in the networking code.)

Thanks,

Ingo