x86, kexec: fix crashdump panic with CONFIG_KEXEC_JUMP

Tim Starling reported that crashdump will panic with kernel compiled
with CONFIG_KEXEC_JUMP due to null pointer deference in
machine_kexec_32.c: machine_kexec(), when deferencing
kexec_image. Refering to:

http://bugzilla.kernel.org/show_bug.cgi?id=13265

This patch fixes the BUG via replacing global variable reference:
kexec_image in machine_kexec() with local variable reference: image,
which is more appropriate, and will not be null.

Same BUG is in machine_kexec_64.c too, so fixed too in the same way.

[ Impact: fix crash on kexec ]

Reported-by: Tim Starling <tstarling@wikimedia.org>
Signed-off-by: Huang Ying <ying.huang@intel.com>
LKML-Reference: <1241751101.6259.85.camel@yhuang-dev.sh.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/machine_kexec_32.c

@@ -194,7 +194,7 @@ void machine_kexec(struct kimage *image)
 				       unsigned int preserve_context);
 
 #ifdef CONFIG_KEXEC_JUMP
-	if (kexec_image->preserve_context)
+	if (image->preserve_context)
 		save_processor_state();
 #endif
 
@@ -253,7 +253,7 @@ void machine_kexec(struct kimage *image)
 					   image->preserve_context);
 
 #ifdef CONFIG_KEXEC_JUMP
-	if (kexec_image->preserve_context)
+	if (image->preserve_context)
 		restore_processor_state();
 #endif
 

arch/x86/kernel/machine_kexec_64.c

@@ -274,7 +274,7 @@ void machine_kexec(struct kimage *image)
 	int save_ftrace_enabled;
 
 #ifdef CONFIG_KEXEC_JUMP
-	if (kexec_image->preserve_context)
+	if (image->preserve_context)
 		save_processor_state();
 #endif
 
@@ -333,7 +333,7 @@ void machine_kexec(struct kimage *image)
 				       image->preserve_context);
 
 #ifdef CONFIG_KEXEC_JUMP
-	if (kexec_image->preserve_context)
+	if (image->preserve_context)
 		restore_processor_state();
 #endif