linux-kernel - Re: [PATCH v2 6/7] EDAC: add edac_check_mc

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Date:   Fri, 4 Aug 2017 21:35:05 +0000
From:   "Kani, Toshimitsu" <toshi.kani@....com>
To:     "bp@...en8.de" <bp@...en8.de>
CC:     "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 6/7] EDAC: add edac_check_mc_owner() to check MC owner

On Fri, 2017-08-04 at 10:30 +0200, Borislav Petkov wrote:
> On Thu, Aug 03, 2017 at 03:57:52PM -0600, Toshi Kani wrote:
> > Only a single edac driver can be enabled for EDAC MC.  When
> > ghes_edac is enabled, a regular edac driver for the CPU type /
> > platform still attempts to register itself and fails in
> > edac_mc_add_mc().
> > 
> > Add edac_check_mc_owner() so that regular edac drivers can check
> > the owner of EDAC MC at the beginning of initialization.
> > 
> > Also change the owner check to string comparison from address
> > check.
> > 
> > Signed-off-by: Toshi Kani <toshi.kani@....com>
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
> > Cc: Tony Luck <tony.luck@...el.com>
> > ---
> >  drivers/edac/edac_mc.c |   15 ++++++++++++++-
> >  drivers/edac/edac_mc.h |   12 ++++++++++++
> >  2 files changed, 26 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/edac/edac_mc.c b/drivers/edac/edac_mc.c
> > index 4800721..52d8d5e 100644
> > --- a/drivers/edac/edac_mc.c
> > +++ b/drivers/edac/edac_mc.c
> > @@ -701,6 +701,19 @@ struct mem_ctl_info *edac_mc_find(int idx)
> >  }
> >  EXPORT_SYMBOL(edac_mc_find);
> >  
> > +/*
> > + * Returns:
> > + *	1 when EDAC MC is free or owned by the module name
> 
> 1 for free OR owned?!? WTF?

1 means the caller's init function can continue its initialization --
such conditions are free or owned by itself.

> > + *	0 when EDAC MC is owned by other module
> > + */
> > +int edac_check_mc_owner(const char *mod_name)
> > +{
> > +	if (edac_mc_owner && strcmp(edac_mc_owner, mod_name))
> 
> strncmp() of course, with sensible maximal string length.

strcmp() breaks when either edac_mc_owner or mod_name string ends. 
strncmp() assumes mod_name string is valid for a given length.  Hence,
the caller needs to supply the length to this function by adding a new
arg 'length', which does not make it any safer.  I think using
strncmp() would require all edac drivers to declare a pre-defined
length of module name...

> > +		return 0;
> > +
> > +	return 1;
> > +}
> > +EXPORT_SYMBOL(edac_check_mc_owner);
> 
> EXPORT_SYMBOL_GPL

Will do.

> >  
> >  /* FIXME - should a warning be printed if no error detection?
> > correction? */
> >  int edac_mc_add_mc_with_groups(struct mem_ctl_info *mci,
> > @@ -742,7 +755,7 @@ int edac_mc_add_mc_with_groups(struct
> > mem_ctl_info *mci,
> >  #endif
> >  	mutex_lock(&mem_ctls_mutex);
> >  
> > -	if (edac_mc_owner && edac_mc_owner != mci->mod_name) {
> > +	if (!edac_check_mc_owner(mci->mod_name)) {
> >  		ret = -EPERM;
> >  		goto fail0;
> >  	}
> > diff --git a/drivers/edac/edac_mc.h b/drivers/edac/edac_mc.h
> > index 5357800..0e95eba 100644
> > --- a/drivers/edac/edac_mc.h
> > +++ b/drivers/edac/edac_mc.h
> > @@ -128,6 +128,18 @@ struct mem_ctl_info *edac_mc_alloc(unsigned
> > mc_num,
> >  				   unsigned sz_pvt);
> >  
> >  /**
> > + *
> > + * edac_check_mc_owner - Check the owner of EDAC MC
> > + *
> > + * @mod_name: pointer to the module name
> > + *
> > + * Returns:
> > + *	1 when EDAC MC is free or owned by the module name
> > + *	0 when EDAC MC is owned by other module
> > + */
> 
> Documenting that function only once is enough.

I personally prefer to document in .c, but since other funcs documented
in dac_mc.h, I will keep the same style.  Will remove the document in
edac_mc.c. 

> > +extern int edac_check_mc_owner(const char *mod_name);
> > +
> > +/*
> >   * edac_mc_add_mc_with_groups() - Insert the @mci structure into
> > the mci
> >   *	global list and create sysfs entries associated with
> > @mci structure.
> >   *

Thanks,
-Toshi