ia64: Make flush_tlb_mm() work for multi-threaded address-spaces on SMP machines.

arch/ia64/kernel/smp.c

@@ -210,6 +210,18 @@ smp_flush_tlb_all (void)
 	local_flush_tlb_all();
 }
 
+void
+smp_flush_tlb_mm (struct mm_struct *mm)
+{
+	local_flush_tlb_mm(mm);
+
+	/* this happens for the common case of a single-threaded fork():  */
+	if (likely(mm == current->active_mm && atomic_read(&mm->mm_users) == 1))
+		return;
+
+	smp_call_function((void (*)(void *))local_flush_tlb_mm, mm, 1, 1);
+}
+
 /*
  * Run a function on another CPU
  *  <func>	The function to run. This must be fast and non-blocking.

include/asm-ia64/tlbflush.h

@@ -26,25 +26,42 @@ extern void local_flush_tlb_all (void);
 
 #ifdef CONFIG_SMP
   extern void smp_flush_tlb_all (void);
+  extern void smp_flush_tlb_mm (struct mm_struct *mm);
 # define flush_tlb_all()	smp_flush_tlb_all()
 #else
 # define flush_tlb_all()	local_flush_tlb_all()
 #endif
 
+static inline void
+local_flush_tlb_mm (struct mm_struct *mm)
+{
+	if (mm == current->active_mm) {
+		get_new_mmu_context(mm);
+		reload_context(mm);
+	}
+}
+
 /*
- * Flush a specified user mapping
+ * Flush a specified user mapping.  This is called, e.g., as a result of fork() and
+ * exit().  fork() ends up here because the copy-on-write mechanism needs to write-protect
+ * the PTEs of the parent task.
  */
 static inline void
 flush_tlb_mm (struct mm_struct *mm)
 {
-	if (mm) {
-		mm->context = 0;
-		if (mm == current->active_mm) {
-			/* This is called, e.g., as a result of exec().  */
-			get_new_mmu_context(mm);
-			reload_context(mm);
-		}
-	}
+	if (!mm)
+		return;
+
+	mm->context = 0;
+
+	if (atomic_read(&mm->mm_users) == 0)
+		return;		/* happens as a result of exit_mmap() */
+
+#ifdef CONFIG_SMP
+	smp_flush_tlb_mm(mm);
+#else
+	local_flush_tlb_mm(mm);
+#endif
 }
 
 extern void flush_tlb_range (struct vm_area_struct *vma, unsigned long start, unsigned long end);