WebSVN – HelenOS-historic – Diff – /kernel/trunk/generic/src/mm/as.c

+{
     as_area_t *area;
     ipl_t ipl;
     ipl = interrupts_disable();
-    spinlock_lock(&as->lock);
+    page_table_lock(as, true);
     area = find_area_and_lock(as, page);
     if (!area) {
         panic("page not part of any as_area\n");
+    }
     page_mapping_insert(as, page, frame, get_area_flags(area));
     spinlock_unlock(&area->lock);
-    spinlock_unlock(&as->lock);
+    page_table_unlock(as, true);
     interrupts_restore(ipl);
+}
 /** Handle page fault within the current address space.
+ *
+ *
  * @return 0 on page fault, 1 on success.
  */
 int as_page_fault(__address page)
+{
+    pte_t *pte;
     as_area_t *area;
     __address frame;
     ASSERT(AS);
     spinlock_lock(&AS->lock);
     area = find_area_and_lock(AS, page);
     if (!area) {
         /*
          * No area contained mapping for 'page'.
          * Signal page fault to low-level handler.
          */
         spinlock_unlock(&AS->lock);
         return 0;
+    }
+    page_table_lock(AS, false);
+    /*
+     * To avoid race condition between two page faults
+     * on the same address, we need to make sure
+     * the mapping has not been already inserted.
+     */
+    if ((pte = page_mapping_find(AS, page))) {
+        if (PTE_PRESENT(pte)) {
+            page_table_unlock(AS, false);
+            spinlock_unlock(&area->lock);
+            spinlock_unlock(&AS->lock);
+            return 1;
+        }
+    }
     /*
      * In general, there can be several reasons that
      * can have caused this fault.
+     *
      * - non-existent mapping: the area is a scratch
      * Map 'page' to 'frame'.
      * Note that TLB shootdown is not attempted as only new information is being
      * inserted into page tables.
      */
     page_mapping_insert(AS, page, frame, get_area_flags(area));
+    page_table_unlock(AS, false);
     spinlock_unlock(&area->lock);
     spinlock_unlock(&AS->lock);
     return 1;
+}
 /** Switch address spaces.
+ *
         ASSERT(as_operations->page_table_create);
         return as_operations->page_table_create(flags);
+}
+/** Lock page table.
+ *
+ * This function should be called before any page_mapping_insert(),
+ * page_mapping_remove() and page_mapping_find().
+ *
+ * Locking order is such that address space areas must be locked
+ * prior to this call. Address space can be locked prior to this
+ * call in which case the lock argument is false.
+ *
+ * @param as Address space.
+ * @param as_locked If false, do not attempt to lock as->lock.
+ */
+void page_table_lock(as_t *as, bool lock)
+{
+    ASSERT(as_operations);
+    ASSERT(as_operations->page_table_lock);
+    as_operations->page_table_lock(as, lock);
+}
+/** Unlock page table.
+ *
+ * @param as Address space.
+ * @param as_locked If false, do not attempt to unlock as->lock.
+ */
+void page_table_unlock(as_t *as, bool unlock)
+{
+    ASSERT(as_operations);
+    ASSERT(as_operations->page_table_unlock);
+    as_operations->page_table_unlock(as, unlock);
+}
 /** Find address space area and change it.
+ *
  * @param as Address space.
  * @param address Virtual address belonging to the area to be changed. Must be page-aligned.
  * @param size New size of the virtual memory block starting at address.
             pte_t *pte;
             /*
              * Releasing physical memory.
              * This depends on the fact that the memory was allocated using frame_alloc().
              */
+            page_table_lock(as, false);
             pte = page_mapping_find(as, area->base + i*PAGE_SIZE);
             if (pte && PTE_VALID(pte)) {
+                __address frame;
                 ASSERT(PTE_PRESENT(pte));
-                frame_free(ADDR2PFN(PTE_GET_FRAME(pte)));
+                frame = PTE_GET_FRAME(pte);
                 page_mapping_remove(as, area->base + i*PAGE_SIZE);
+                page_table_unlock(as, false);
+                frame_free(ADDR2PFN(frame));
+            } else {
+                page_table_unlock(as, false);
+            }
+        }
         /*
          * Invalidate TLB's.
          */

Subversion Repositories HelenOS-historic

(root)/kernel/trunk/generic/src/mm/as.c – Rev 1026 → 1044