Fix incoherent LDT at mmap exit.

We should _not_ update the current LDT if it's not the current
MM that we are tearing down.

arch/i386/kernel/ldt.c

@@ -107,7 +107,8 @@ int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 void release_segments(struct mm_struct *mm)
 {
 	if (mm->context.size) {
-		clear_LDT();
+		if (mm == current->active_mm)
+			clear_LDT();
 		if (mm->context.size*LDT_ENTRY_SIZE > PAGE_SIZE)
 			vfree(mm->context.ldt);
 		else

arch/x86_64/kernel/ldt.c

@@ -132,7 +132,8 @@ int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 void release_segments(struct mm_struct *mm)
 {
 	if (mm->context.size) {
-		clear_LDT();
+		if (mm == current->active_mm)
+			clear_LDT();
 		if (mm->context.size*LDT_ENTRY_SIZE > PAGE_SIZE)
 			vfree(mm->context.ldt);
 		else