linux-kernel - Re: [PATCH v3] kexec: Make a pair of map and unmap reserved pages when kdump fails to start

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Message-ID: <20150710102850.06041275@holzheu>
Date:	Fri, 10 Jul 2015 10:28:50 +0200
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Minfei Huang <mnfhuang@...il.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, ebiederm@...ssion.com,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
	linux390@...ibm.com, linux-s390@...r.kernel.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] kexec: Make a pair of map and unmap reserved pages
 when kdump fails to start

On Fri, 10 Jul 2015 12:05:27 +0800
Minfei Huang <mnfhuang@...il.com> wrote:

> On 07/09/15 at 05:54P, Michael Holzheu wrote:
> > On Tue, 7 Jul 2015 17:18:40 -0400
> > Vivek Goyal <vgoyal@...hat.com> wrote:
> > 
> > > On Thu, Jul 02, 2015 at 09:45:52AM +0800, Minfei Huang wrote:
> > 
> > [snip]
> > 
> > > I am thinking of moving kernel loading code in a separate function to
> > > make things little simpler. Right now it is confusing.
> > > 
> > > Can you please test attached patch. I have only compile tested it. This
> > > is primarily doing what you are doing but in a separate function. It
> > > seems more readable now.
> > 
> > The patch looks good to me. What about the following patch on top
> > to make things even more readable?
> > ---
> >  kernel/kexec.c |   50 +++++++++++++++++---------------------------------
> >  1 file changed, 17 insertions(+), 33 deletions(-)
> > 
> > --- a/kernel/kexec.c
> > +++ b/kernel/kexec.c
> > @@ -1236,14 +1236,18 @@ int kexec_load_disabled;
> >  
> >  static DEFINE_MUTEX(kexec_mutex);
> >  
> > -static int __kexec_load(struct kimage **rimage, unsigned long entry,
> > -			unsigned long nr_segments,
> > +static int __kexec_load(unsigned long entry, unsigned long nr_segments,
> >  			struct kexec_segment __user * segments,
> >  			unsigned long flags)
> >  {
> > +	struct kimage *image, **dest_image;
> >  	unsigned long i;
> >  	int result;
> > -	struct kimage *image;
> > +
> > +	dest_image = (flags & KEXEC_ON_CRASH) ? &kexec_crash_image : &kexec_image;
> > +
> > +	if (nr_segments == 0)
> > +		return 0;
> 
> It is fine, if nr_segments is 0. So we should deal with this case like
> original kexec code.
> 
> >  
> >  	if (flags & KEXEC_ON_CRASH) {
> >  		/*
> > @@ -1251,7 +1255,6 @@ static int __kexec_load(struct kimage **
> >  		 * crashes.  Free any current crash dump kernel before
> >  		 * we corrupt it.
> >  		 */
> > -
> >  		kimage_free(xchg(&kexec_crash_image, NULL));
> >  	}
> >  
> > @@ -1267,30 +1270,29 @@ static int __kexec_load(struct kimage **
> >  
> >  	result = machine_kexec_prepare(image);
> >  	if (result)
> > -		goto out;
> > +		goto fail;
> >  
> >  	for (i = 0; i < nr_segments; i++) {
> >  		result = kimage_load_segment(image, &image->segment[i]);
> >  		if (result)
> > -			goto out;
> > +			goto fail;
> >  	}
> > -
> >  	kimage_terminate(image);
> > -	*rimage = image;
> > -out:
> > +	/* Install the new kernel, and  uninstall the old */
> > +	kimage_free(xchg(dest_image, image));
> >  	if (flags & KEXEC_ON_CRASH)
> >  		crash_unmap_reserved_pages();
> > -
> > -	/* Free image if there was an error */
> > -	if (result)
> > -		kimage_free(image);
> > +	return 0;
> > +fail:
> > +	if (flags & KEXEC_ON_CRASH)
> > +		crash_unmap_reserved_pages();
> > +	kimage_free(image);
> 
> Kernel release image again

Again? This is only done in the error case.

> , and will crash in here, since we do not
> assign the image to NULL when we release the image above.

Good catch, I should have set image=NULL at the beginning of __kexec_load().

Michael

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