linux-kernel - RE: [PATCH][v6] PM / hibernate: Print the possible panic reason when resuming with inconsistent e820 map

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Date:   Sun, 28 Aug 2016 13:08:02 +0000
From:   "Chen, Yu C" <yu.c.chen@...el.com>
To:     Pavel Machek <pavel@....cz>
CC:     joeyli <jlee@...e.com>, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH][v6] PM / hibernate: Print the possible panic reason
 when resuming with inconsistent e820 map

> -----Original Message-----
> From: Pavel Machek [mailto:pavel@....cz]
> Sent: Sunday, August 28, 2016 8:48 PM
> To: Chen, Yu C
> Cc: joeyli; Rafael J. Wysocki; linux-pm@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCH][v6] PM / hibernate: Print the possible panic reason when
> resuming with inconsistent e820 map
> 
> On Sun 2016-08-28 10:07:10, Chen Yu wrote:
> > Hi,
> > On Fri, Aug 26, 2016 at 09:56:54PM +0200, Pavel Machek wrote:
> > > Hi!
> > >
> > > > > > > What's the progress of this patch? Looks already have experts
> review it.
> > > > > > > Why this patch didn't accept?
> > > > > > This patch is a little overkilled, and I have saved another
> > > > > > simpler version to only check the md5 hash (as people suggested) for
> it. I can post it later.
> > > > > >
> > > > >
> > > > > I am happy to test and review it.
> > > > >
> > > > Here it is. As Rafael is on travel, it would be grateful if you
> > > > can give some advance on this, thanks!
> > >
> > > Better than last one.
> > >
> > > > +		return -ENOMEM;
> > > > +
> > > > +	req = ahash_request_alloc(tfm, GFP_ATOMIC);
> > >
> > > what context is this called from? GFP_ATOMIC allocations like to fail...
> > >
> > It is in normal process context, OK, I'll change it to GFP_KERNEL.
> > > > +static int hibernation_e820_check(void *buf) {
> > > > +	int ret;
> > > > +	char result[MD5_HASH_SIZE] = {0};
> > > > +
> > > > +	ret = get_e820_md5(&e820_saved, result);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	if (memcmp(result, buf, MD5_HASH_SIZE))
> > > > +		e820_conflict = true;
> > >
> > > Passing return value using global variable is ugly. Can you just
> > > print the warning and kill the box here?
> > Do you mean get rid of the panic hooker and just print the warning
> > here?
> 
> Yep, I'd do that... (And you probably want to rise the severity).
Sometime the users might not be able to see the warning during resume(too fast)
and got a system panic later, so I was thinking if it might help user to see the warning
in panic too, how about this:

if (memcmp(result, buf, MD5_DIGEST_SIZE)) {
	pr_err("PM: e820 map conflict detected!\n");
	register_die_notifier(&hibernation_die_notifier);
} 
So we can print warning in hibernation_die_notifier without introducing a global variable?

Thanks,
Yu