[IA64] fix stack unwinder.

The stack unwinder can be called in interrupt context. On the other
hand xmalloc() can't be called in interrupt context.
Don't call xmalloc() if in the interrupt context.

Signed-off-by: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>

diff -r 63107bf2c6e4 xen/arch/ia64/linux-xen/unwind.c
--- a/xen/arch/ia64/linux-xen/unwind.c	Thu Aug 07 18:27:44 2008 +0900
+++ b/xen/arch/ia64/linux-xen/unwind.c	Thu Aug 07 18:29:31 2008 +0900
@@ -91,9 +91,9 @@
 #endif
 
 #ifdef XEN
-#define alloc_reg_state()	xmalloc(struct unw_reg_state)
+#define alloc_reg_state()	({in_irq()? NULL: xmalloc(struct unw_reg_state);})
 #define free_reg_state(usr)	xfree(usr)
-#define alloc_labeled_state()	xmalloc(struct unw_labeled_state)
+#define alloc_labeled_state()	({in_irq()? NULL: xmalloc(struct unw_labeled_state);})
 #define free_labeled_state(usr)	xfree(usr)
 #else
 #define alloc_reg_state()	kmalloc(sizeof(struct unw_reg_state), GFP_ATOMIC)