linux-kernel - Re: [PATCH v4] kexec: Make a pair of map and unmap reserved pages when kdump fails to start

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Message-ID: <20150710090322.GA5138@dhcp-128-21.nay.redhat.com>
Date:	Fri, 10 Jul 2015 17:03:22 +0800
From:	Minfei Huang <mnfhuang@...il.com>
To:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Cc:	ebiederm@...ssion.com, vgoyal@...hat.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 v4] kexec: Make a pair of map and unmap reserved pages
 when kdump fails to start

On 07/10/15 at 10:54P, Michael Holzheu wrote:
> On Fri, 10 Jul 2015 13:12:17 +0800
> Minfei Huang <mnfhuang@...il.com> wrote:
> 
> > For some arch, kexec shall map the reserved pages, then use them, when
> > we try to start the kdump service.
> > 
> > Now kexec will never unmap the reserved pages, once it fails to continue
> > starting the kdump service. So we make a pair of map/unmap reserved
> > pages whatever kexec fails or not in code path.
> > 
> > In order to make code readable, wrap a new function __kexec_load which
> > contains all of the logic to deal with the image loading.
> > 
> > Signed-off-by: Minfei Huang <mnfhuang@...il.com>
> > ---
> > v3:
> > - reconstruct the patch, wrap a new function to deal with the code logic, based on Vivek and Michael's patch
> > v2:
> > - replace the "failure" label with "fail_unmap_pages"
> > v1:
> > - reconstruct the patch code
> > ---
> >  kernel/kexec.c | 112 ++++++++++++++++++++++++++++++++-------------------------
> >  1 file changed, 63 insertions(+), 49 deletions(-)
> > 
> > diff --git a/kernel/kexec.c b/kernel/kexec.c
> > index a785c10..2232c90 100644
> > --- a/kernel/kexec.c
> > +++ b/kernel/kexec.c
> > @@ -1247,10 +1247,71 @@ int kexec_load_disabled;
> > 
> >  static DEFINE_MUTEX(kexec_mutex);
> > 
> > +static int __kexec_load(unsigned long entry, unsigned long nr_segments,
> > +			struct kexec_segment __user *segments,
> > +			unsigned long flags)
> > +{
> > +	int result = 0;
> > +	struct kimage **dest_image, *image;
> > +
> > +	dest_image = &kexec_image;
> > +
> > +	if (flags & KEXEC_ON_CRASH)
> > +		dest_image = &kexec_crash_image;
> > +
> > +	if (nr_segments == 0) {
> > +		/* Install the new kernel, and  Uninstall the old */
> > +		image = xchg(dest_image, image);
> > +		kimage_free(image);
> 
> Well this is wrong and should probably be:
> 
>         if (nr_segments == 0) {
>                 /* Uninstall image */
>                 image = xchg(dest_image, NULL);
>                 kimage_free(image);
> 

You are right. It should be what you commented.

> > +	} else {
> > +		unsigned long i;
> > +
> > +		if (flags & KEXEC_ON_CRASH) {
> > +			/*
> 
> [snip]
> 
> > +			result = kimage_load_segment(image, &image->segment[i]);
> > +			if (result)
> > +				goto failure_unmap_mem;
> > +		}
> > +
> > +		kimage_terminate(image);
> > +
> > +		/* Install the new kernel, and  Uninstall the old */
> 
> Perhaps fix the comment: Remove superfluous blank and lowercase "uninstall"?
> 

Thanks.
Minfei
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