linux-kernel - Re: [PATCH v5 12/18] x86/intel_rdt: Add "info" files to resctrl file system

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Date:   Thu, 27 Oct 2016 20:25:57 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
cc:     "H. Peter Anvin" <h.peter.anvin@...el.com>,
        Ingo Molnar <mingo@...e.hu>, Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Nilay Vaish <nilayvaish@...il.com>, Shaohua Li <shli@...com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Sai Prakhya <sai.praneeth.prakhya@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v5 12/18] x86/intel_rdt: Add "info" files to resctrl file
 system



On Thu, 27 Oct 2016, Fenghua Yu wrote:

> On Wed, Oct 26, 2016 at 04:45:50PM +0200, Thomas Gleixner wrote:
> > On Sat, 22 Oct 2016, Fenghua Yu wrote:
> > > +/*
> > > + * Forcibly remove all of subdirectories under root.
> > > + */
> > > +static void rmdir_all_sub(void)
> > > +{
> > > +	kernfs_remove(kn_info);
> > 
> > What clears kn_info?
> 
> Is the question "Why clears kn_info?"
> 
> kn_info is created during mount time and has different contents
> under "info" directory with CDP enabled or disabled by mount parameter "cdp".
> 
> umount needs to remove kn_info so that it's ready to be created next time
> during mount time. So user can do CAT mount, check "info", umount, and then
> CDP mount, check "info". The user will see different contents in two "info"
> checks.

Lemme rephrase. What does: kn_info = NULL; ?

We should clear static variables for correctness sake. The current code has
no problem with that, but 5 month down the road something is going to trip
over the stale reference.

Thanks,

	tglx