mm/map: limit the count of memory mapping for the task

No memory map count limit that will exhaust memory and cause
the system hang. Also that fix pass LTP posix case mmap/24-1.c

Signed-off-by: fangxinyong <fangxinyong@xiaomi.com>

mm/map/Make.defs

@@ -26,7 +26,7 @@ ifeq ($(CONFIG_ARCH_VMA_MAPPING),y)
 CSRCS += vm_region.c
 endif
 
-# Add the shared memory directory to the build
+# Add the map directory to the build
 
 DEPPATH += --dep-path map
 VPATH += :map

mm/map/mm_map.c

@@ -93,6 +93,7 @@ void mm_map_initialize(FAR struct mm_map_s *mm, bool kernel)
 {
   sq_init(&mm->mm_map_sq);
   nxrmutex_init(&mm->mm_map_mutex);
+  mm->map_count = 0;
 
   /* Create the virtual pages allocator for user process */
 
@@ -148,9 +149,13 @@ void mm_map_destroy(FAR struct mm_map_s *mm)
             }
         }
 
+      mm->map_count--;
+
       kmm_free(entry);
     }
 
+  DEBUGASSERT(mm->map_count == 0);
+
   nxrmutex_destroy(&mm->mm_map_mutex);
 
   /* Release the virtual pages allocator */
@@ -198,6 +203,17 @@ int mm_map_add(FAR struct mm_map_s *mm, FAR struct mm_map_entry_s *entry)
       return ret;
     }
 
+  /* Too many mappings? */
+
+  if (mm->map_count >= CONFIG_MM_MAP_COUNT_MAX)
+    {
+      kmm_free(new_entry);
+      nxrmutex_unlock(&mm->mm_map_mutex);
+      return -ENOMEM;
+    }
+
+  mm->map_count++;
+
   sq_addfirst((sq_entry_t *)new_entry, &mm->mm_map_sq);
 
   nxrmutex_unlock(&mm->mm_map_mutex);
@@ -309,6 +325,7 @@ int mm_map_remove(FAR struct mm_map_s *mm,
   if (entry == prev_entry)
     {
       sq_remfirst(&mm->mm_map_sq);
+      mm->map_count--;
       removed_entry = prev_entry;
     }
   else
@@ -321,6 +338,7 @@ int mm_map_remove(FAR struct mm_map_s *mm,
           if (entry == removed_entry)
             {
               sq_remafter((sq_entry_t *)prev_entry, &mm->mm_map_sq);
+              mm->map_count--;
               break;
             }