[PATCH] mm: fix a race condition under SMC + COW

[linux-2.6-microblaze.git] / mm / memory.c

diff --git a/mm/memory.c b/mm/memory.c
index f2ef1dc..160f5b5 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1577,7 +1577,14 @@ gotten:
                entry = mk_pte(new_page, vma->vm_page_prot);
                entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                lazy_mmu_prot_update(entry);
-               ptep_establish(vma, address, page_table, entry);
+               /*
+                * Clear the pte entry and flush it first, before updating the
+                * pte with the new entry. This will avoid a race condition
+                * seen in the presence of one thread doing SMC and another
+                * thread doing COW.
+                */
+               ptep_clear_flush(vma, address, page_table);
+               set_pte_at(mm, address, page_table, entry);
                update_mmu_cache(vma, address, entry);
                lru_cache_add_active(new_page);
                page_add_new_anon_rmap(new_page, vma, address);
@@ -2604,3 +2611,56 @@ int in_gate_area_no_task(unsigned long addr)
 }
 
 #endif /* __HAVE_ARCH_GATE_AREA */
+
+/*
+ * Access another process' address space.
+ * Source/target buffer must be kernel space,
+ * Do not walk the page table directly, use get_user_pages
+ */
+int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
+{
+       struct mm_struct *mm;
+       struct vm_area_struct *vma;
+       struct page *page;
+       void *old_buf = buf;
+
+       mm = get_task_mm(tsk);
+       if (!mm)
+               return 0;
+
+       down_read(&mm->mmap_sem);
+       /* ignore errors, just check how much was sucessfully transfered */
+       while (len) {
+               int bytes, ret, offset;
+               void *maddr;
+
+               ret = get_user_pages(tsk, mm, addr, 1,
+                               write, 1, &page, &vma);
+               if (ret <= 0)
+                       break;
+
+               bytes = len;
+               offset = addr & (PAGE_SIZE-1);
+               if (bytes > PAGE_SIZE-offset)
+                       bytes = PAGE_SIZE-offset;
+
+               maddr = kmap(page);
+               if (write) {
+                       copy_to_user_page(vma, page, addr,
+                                         maddr + offset, buf, bytes);
+                       set_page_dirty_lock(page);
+               } else {
+                       copy_from_user_page(vma, page, addr,
+                                           buf, maddr + offset, bytes);
+               }
+               kunmap(page);
+               page_cache_release(page);
+               len -= bytes;
+               buf += bytes;
+               addr += bytes;
+       }
+       up_read(&mm->mmap_sem);
+       mmput(mm);
+
+       return buf - old_buf;
+}