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: <20150708120638.GA8672@dhcp-128-42.nay.redhat.com>
Date:	Wed, 8 Jul 2015 20:06:38 +0800
From:	Minfei Huang <mnfhuang@...il.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	ebiederm@...ssion.com, schwidefsky@...ibm.com,
	heiko.carstens@...ibm.com, linux390@...ibm.com,
	holzheu@...ux.vnet.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 07/07/15 at 05:18P, Vivek Goyal wrote:
> On Thu, Jul 02, 2015 at 09:45:52AM +0800, Minfei Huang 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.
> > 
> > Make a pair of reserved pages in kdump starting path, whatever kexec
> > fails or not.
> > 
> > Signed-off-by: Minfei Huang <mnfhuang@...il.com>
> > ---
> > v2:
> > - replace the "failure" label with "fail_unmap_pages"
> > v1:
> > - reconstruct the patch code
> > ---
> >  kernel/kexec.c | 26 ++++++++++++++------------
> >  1 file changed, 14 insertions(+), 12 deletions(-)
> > 
> 
> Hi Minfei,
> 
> I am thinking of moving kernel loading code in a separate function to
> make things little simpler. Right now it is confusing.

In my patch, I think maybe the label confuses with the reviewer, which
does not express the intention clearly. 

> 
> 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 passed the simple testcase. Since it does change the code
logic, I think there is no risky.

Thanks
Minfei

> Thanks
> Vivek
> 
> 
> ---
>  kernel/kexec.c |   90 +++++++++++++++++++++++++++++++++++----------------------
>  1 file changed, 56 insertions(+), 34 deletions(-)
> 
> Index: rhvgoyal-linux/kernel/kexec.c
> ===================================================================
> --- rhvgoyal-linux.orig/kernel/kexec.c	2015-07-06 13:59:35.088129148 -0400
> +++ rhvgoyal-linux/kernel/kexec.c	2015-07-07 17:14:23.593175644 -0400
> @@ -1247,6 +1247,57 @@ int kexec_load_disabled;
>  
>  static DEFINE_MUTEX(kexec_mutex);
>  
> +static int __kexec_load(struct kimage **rimage, unsigned long entry,
> +			unsigned long nr_segments,
> +			struct kexec_segment __user * segments,
> +			unsigned long flags)
> +{
> +	unsigned long i;
> +	int result;
> +	struct kimage *image;
> +
> +	if (flags & KEXEC_ON_CRASH) {
> +		/*
> +		 * Loading another kernel to switch to if this one
> +		 * crashes.  Free any current crash dump kernel before
> +		 * we corrupt it.
> +		 */
> +
> +		kimage_free(xchg(&kexec_crash_image, NULL));
> +	}
> +
> +	result = kimage_alloc_init(&image, entry, nr_segments, segments, flags);
> +	if (result)
> +		return result;
> +
> +	if (flags & KEXEC_ON_CRASH)
> +		crash_map_reserved_pages();
> +
> +	if (flags & KEXEC_PRESERVE_CONTEXT)
> +		image->preserve_context = 1;
> +
> +	result = machine_kexec_prepare(image);
> +	if (result)
> +		goto out;
> +
> +	for (i = 0; i < nr_segments; i++) {
> +		result = kimage_load_segment(image, &image->segment[i]);
> +		if (result)
> +			goto out;
> +	}
> +
> +	kimage_terminate(image);
> +	*rimage = image;
> +out:
> +	if (flags & KEXEC_ON_CRASH)
> +		crash_unmap_reserved_pages();
> +
> +	/* Free image if there was an error */
> +	if (result)
> +		kimage_free(image);
> +	return result;
> +}
> +
>  SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
>  		struct kexec_segment __user *, segments, unsigned long, flags)
>  {
> @@ -1292,44 +1343,15 @@ SYSCALL_DEFINE4(kexec_load, unsigned lon
>  	dest_image = &kexec_image;
>  	if (flags & KEXEC_ON_CRASH)
>  		dest_image = &kexec_crash_image;
> -	if (nr_segments > 0) {
> -		unsigned long i;
>  
> -		if (flags & KEXEC_ON_CRASH) {
> -			/*
> -			 * Loading another kernel to switch to if this one
> -			 * crashes.  Free any current crash dump kernel before
> -			 * we corrupt it.
> -			 */
> -
> -			kimage_free(xchg(&kexec_crash_image, NULL));
> -			result = kimage_alloc_init(&image, entry, nr_segments,
> -						   segments, flags);
> -			crash_map_reserved_pages();
> -		} else {
> -			/* Loading another kernel to reboot into. */
> -
> -			result = kimage_alloc_init(&image, entry, nr_segments,
> -						   segments, flags);
> -		}
> -		if (result)
> -			goto out;
> -
> -		if (flags & KEXEC_PRESERVE_CONTEXT)
> -			image->preserve_context = 1;
> -		result = machine_kexec_prepare(image);
> +	/* Load new kernel */
> +	if (nr_segments > 0) {
> +		result = __kexec_load(&image, entry, nr_segments, segments,
> +				      flags);
>  		if (result)
>  			goto out;
> -
> -		for (i = 0; i < nr_segments; i++) {
> -			result = kimage_load_segment(image, &image->segment[i]);
> -			if (result)
> -				goto out;
> -		}
> -		kimage_terminate(image);
> -		if (flags & KEXEC_ON_CRASH)
> -			crash_unmap_reserved_pages();
>  	}
> +
>  	/* Install the new kernel, and  Uninstall the old */
>  	image = xchg(dest_image, image);
>  
--
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