linux-kernel - Re: [PATCH 2/5] x86/intel_rdt: Add diagnostics when writing the schemata file

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Date:   Tue, 26 Sep 2017 00:12:46 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Luck, Tony" <tony.luck@...el.com>
cc:     linux-kernel@...r.kernel.org, Boris Petkov <bp@...e.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vikas Shivappa <vikas.shivappa@...el.com>
Subject: Re: [PATCH 2/5] x86/intel_rdt: Add diagnostics when writing the
 schemata file

On Mon, 25 Sep 2017, Luck, Tony wrote:
> On Mon, Sep 25, 2017 at 04:04:07PM +0200, Thomas Gleixner wrote:
> > On Mon, 18 Sep 2017, Luck, Tony wrote:
> > > @@ -208,14 +241,19 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
> > >  	char *tok, *resname;
> > >  	int closid, ret = 0;
> > >  
> > > +	seq_buf_clear(&last_cmd_status);
> > > +
> > >  	/* Valid input requires a trailing newline */
> > > -	if (nbytes == 0 || buf[nbytes - 1] != '\n')
> > > +	if (nbytes == 0 || buf[nbytes - 1] != '\n') {
> > > +		seq_buf_puts(&last_cmd_status, "no trailing newline\n");
> > >  		return -EINVAL;
> > > +	}
> > >  	buf[nbytes - 1] = '\0';
> > 
> > In all other instances you access last_cmd_status within the
> > rdtgroup_kn_lock_live() protected section, which also serializes the show()
> > function via rdtgroup_mutex. Here you do it outside for obvious reasons,
> > but that opens a can of evil worms ...
> 
> Indeed.
> 
> > Can you please provide and use two helpers - last_cmd_buf_clear() and
> > last_cmd_buf_puts() - which both have a
> > lockdep_assert_held(&rdtgroup_mutex) inside to make sure that we don't end
> > up with unprotected access accidentally?
> 
> Sure. In progress. But I also need a last_cmd_printf(), which for some
> reason is giving me grief.  In the header file I put:
> 
> +static inline void last_cmd_printf(const char *fmt, ...)
> +{
> +       va_list ap;
> +
> +       va_start(ap, fmt);
> +       lockdep_assert_held(&rdtgroup_mutex);
> +       seq_buf_printf(&last_cmd_status, fmt, ap);

seq_buf_vprintf() is your friend. It takes va_list as last argument.

While at it can you please make it a proper function? No point for inlining
that.

Thanks,

	tglx