Re: [PATCH 1/8] ftrace: add ftrace_init_nop()

From: Steven Rostedt <rostedt@goodmis.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, amit.kachhap@arm.com,
	ard.biesheuvel@linaro.org, catalin.marinas@arm.com,
	deller@gmx.de, duwe@suse.de, james.morse@arm.com,
	jeyu@kernel.org, jpoimboe@redhat.com, jthierry@redhat.com,
	mingo@redhat.com, peterz@infradead.org, svens@stackframe.org,
	takahiro.akashi@linaro.org, will@kernel.org
Subject: Re: [PATCH 1/8] ftrace: add ftrace_init_nop()
Date: Tue, 22 Oct 2019 08:54:28 -0400	[thread overview]
Message-ID: <20191022085428.75cfaad6@gandalf.local.home> (raw)
In-Reply-To: <20191022112811.GA11583@lakrids.cambridge.arm.com>

On Tue, 22 Oct 2019 12:28:11 +0100
Mark Rutland <mark.rutland@arm.com> wrote:

> > To make the name even better, let's just rename it to:
> > 
> >  ftrace_nop_initialization()
> > 
> > I think that may be the best description for it.  
> 
> Perhaps ftrace_nop_initialize(), so that it's not a noun?
> 
> I've made it ftrace_nop_initialization() in my branch for now.

I'm fine with ftrace_nop_initialize().

> 
> > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > > index f296d89be757..afd7e210e595 100644
> > > --- a/kernel/trace/ftrace.c
> > > +++ b/kernel/trace/ftrace.c
> > > @@ -2493,15 +2493,22 @@ struct dyn_ftrace *ftrace_rec_iter_record(struct ftrace_rec_iter *iter)
> > >  	return &iter->pg->records[iter->index];
> > >  }
> > >  
> > > +#ifndef ftrace_init_nop
> > > +static int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
> > > +{
> > > +	return ftrace_make_nop(mod, rec, MCOUNT_ADDR);
> > > +}
> > > +#endif  
> > 
> > Can you place the above in the ftrace.h header. That's where that would
> > belong.
> > 
> > #ifndef ftrace_init_nop
> > struct module;
> > static inline int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
> > {
> > 	return ftrace_make_nop(mod, rec, MCOUNT_ADDR);
> > }
> > #endif  
> 
> True.
> 
> I've put this immediately after ftrace_make_nop() in the header, and
> given it a kerneldoc comment. There's a declaration for struct module at
> the top of the header, so I've just relied on that
> 
> That looks like:
> 
> | /**
> |  * ftrace_init_nop - initialize a nop call site
> |  * @mod: module structure if called by module load initialization
> |  * @rec: the mcount call site record

Perhaps say "mcount/fentry"

> |  *
> |  * This is a very sensitive operation and great care needs
> |  * to be taken by the arch.  The operation should carefully
> |  * read the location, check to see if what is read is indeed
> |  * what we expect it to be, and then on success of the compare,
> |  * it should write to the location.
> |  *
> |  * The code segment at @rec->ip should be as initialized by the

"should be as" is a bit confusing. What about?

 "The code segment at @rec->ip should contain the contents created by
  the compiler".

-- Steve

> |  * compiler
> |  *
> |  * Return must be:
> |  *  0 on success
> |  *  -EFAULT on error reading the location
> |  *  -EINVAL on a failed compare of the contents
> |  *  -EPERM  on error writing to the location
> |  * Any other value will be considered a failure.
> |  */
> | #ifndef ftrace_init_nop
> | static int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
> | {
> | 	return ftrace_make_nop(mod, rec, MCOUNT_ADDR);
> | }
> | #endif
> 
> Thanks,
> Mark.