[PATCH v18 04/13] arm64/kexec: Add pr_debug output

On Wed, 2016-06-15 at 18:14 +0100, James Morse wrote:

On 09/06/16 21:08, Geoff Levand wrote:

quoted

To aid in debugging kexec problems or when adding new functionality to kexec add
a new routine kexec_image_info() and several inline pr_debug statements.

quoted

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
+/**
+ * kexec_is_dtb - Helper routine to check the device tree header signature.
+ */
+static bool kexec_is_dtb(const void *dtb)
+{
+> > 	> > __be32 magic;
+
+> > 	> > if (get_user(magic, (__be32 *)dtb))
+> > 	> > 	> > return false;
+

You pass this function 'kimage->segment[i].buf', this looks like the user space
memory that contained the dtb when kexec-tools first ran to load the image.

This will work when you call it from machine_kexec_prepare(), but by the time we
get to machine_kexec() that process is long gone, and this pointer should be
considered junk.

I don't think its possible to find this information from machine_kexec(), as the
DTB will be split up into page size chunks and scattered through memory.

That's correct.  I don't think it that important to print the
dtb segment, so I'll just remove this kexec_is_dtb() routine.

quoted

+
 void machine_kexec_cleanup(struct kimage *kimage)
 {
 > > 	> > /* Empty routine needed to avoid build errors. */

@@ -65,6 +107,8 @@ int machine_kexec_prepare(struct kimage *kimage)
 > > 	> > 	> > }
 > > 	> > }
 
+> > 	> > kexec_image_info(kimage);
+

You want to put this at the start of machine_kexec_prepare(), otherwise we may
return from:

quoted

#ifdef CONFIG_HOTPLUG_CPU
	> > /* any_cpu as we don't mind being preempted */
	> > int any_cpu = raw_smp_processor_id();

	> > if (cpu_ops[any_cpu]->cpu_die)
	> > 	> > return 0;
#endif /* CONFIG_HOTPLUG_CPU */

This maybe-return-an-error block needs to be the last thing in the function.

OK.

I'm not sure if the debug output is actually useful this early: kexec-tools
prints out exactly the same information shortly after this function returns.

I thought it good to do it here, kexec-tools is not the only user
of kexec see https://github.com/antonblanchard/kexec-lite.

Thanks for checking.

-Geoff