fix: preventing "double-free" condition of a frame

kernel/mem/frame.c

@@ -42,7 +42,7 @@ static void frame_mark_free(int frame) {
     allocator.nb_frames_used--;
 }
 
-static bool is_frame_free(int frame) {
+bool is_frame_free(int frame) {
     int idx_bmp = frame / 8;
     return !(allocator.bitmap[idx_bmp] & (1 << (frame % 8)));
 }
@@ -71,8 +71,10 @@ void frame_init(uint_t RAM_in_KB) {
 }
 
 void frame_free(void *frame_addr) {
+    if (!is_frame_free(ADDR_TO_FRAME_NB(frame_addr))) {
         frame_mark_free(ADDR_TO_FRAME_NB(frame_addr));
     }
+}
 
 uint_t frame_total_free(void) {
     return BITMAP_SIZE * 8 - allocator.nb_frames_used;
@@ -117,25 +119,3 @@ void dbg_frame_allocator(struct terminal_t *term) {
         return;
     }
 }
-
-/*void dbg_frame_bmp(struct terminal_t *term) {*/
-/*    if (term_set_colours(term, YELLOW, BLACK) != 0) {*/
-/*        return;*/
-/*    }*/
-/**/
-/*    int alloc = 0;*/
-/*    for (uint_t i = 0; i < BITMAP_SIZE; i++) {*/
-/*        if (!allocator.bitmap[i]) {*/
-/*            break;*/
-/*        }*/
-/**/
-/*        alloc += allocator.bitmap[i];*/
-/*        kprintf(term, "%d ", allocator.bitmap[i]);*/
-/*    }*/
-/**/
-/*    kprintf(term, "Number of frames allocated = %d\n", alloc);*/
-/**/
-/*    if (term_set_colours(term, WHITE, BLACK) != 0) {*/
-/*        return;*/
-/*    }*/
-/*}*/