---

yaml
---
r: 144362
b: refs/heads/master
c: b827e49
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: a5fc1abe438b87a9d128beebc377f78e2681a76d
+refs/heads/master: b827e496c893de0c0f142abfaeb8730a2fd6b37f

trunk/Documentation/filesystems/Locking

@@ -512,16 +512,24 @@ locking rules:
 		BKL	mmap_sem	PageLocked(page)
 open:		no	yes
 close:		no	yes
-fault:		no	yes
-page_mkwrite:	no	yes		no
+fault:		no	yes		can return with page locked
+page_mkwrite:	no	yes		can return with page locked
 access:		no	yes
 
-	->page_mkwrite() is called when a previously read-only page is
-about to become writeable. The file system is responsible for
-protecting against truncate races. Once appropriate action has been
-taking to lock out truncate, the page range should be verified to be
-within i_size. The page mapping should also be checked that it is not
-NULL.
+	->fault() is called when a previously not present pte is about
+to be faulted in. The filesystem must find and return the page associated
+with the passed in "pgoff" in the vm_fault structure. If it is possible that
+the page may be truncated and/or invalidated, then the filesystem must lock
+the page, then ensure it is not already truncated (the page lock will block
+subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
+locked. The VM will unlock the page.
+
+	->page_mkwrite() is called when a previously read-only pte is
+about to become writeable. The filesystem again must ensure that there are
+no truncate/invalidate races, and then return with the page locked. If
+the page has been truncated, the filesystem should not look up a new page
+like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
+will cause the VM to retry the fault.
 
 	->access() is called when get_user_pages() fails in
 acces_process_vm(), typically used to debug a process through

trunk/fs/buffer.c

@@ -2397,7 +2397,8 @@ block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 	if ((page->mapping != inode->i_mapping) ||
 	    (page_offset(page) > size)) {
 		/* page got truncated out from underneath us */
-		goto out_unlock;
+		unlock_page(page);
+		goto out;
 	}
 
 	/* page is wholly or partially inside EOF */
@@ -2411,14 +2412,15 @@ block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 		ret = block_commit_write(page, 0, end);
 
 	if (unlikely(ret)) {
+		unlock_page(page);
 		if (ret == -ENOMEM)
 			ret = VM_FAULT_OOM;
 		else /* -ENOSPC, -EIO, etc */
 			ret = VM_FAULT_SIGBUS;
-	}
+	} else
+		ret = VM_FAULT_LOCKED;
 
-out_unlock:
-	unlock_page(page);
+out:
 	return ret;
 }
 

trunk/mm/memory.c

@@ -1971,6 +1971,15 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 				ret = tmp;
 				goto unwritable_page;
 			}
+			if (unlikely(!(tmp & VM_FAULT_LOCKED))) {
+				lock_page(old_page);
+				if (!old_page->mapping) {
+					ret = 0; /* retry the fault */
+					unlock_page(old_page);
+					goto unwritable_page;
+				}
+			} else
+				VM_BUG_ON(!PageLocked(old_page));
 
 			/*
 			 * Since we dropped the lock we need to revalidate
@@ -1980,9 +1989,11 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			 */
 			page_table = pte_offset_map_lock(mm, pmd, address,
 							 &ptl);
-			page_cache_release(old_page);
-			if (!pte_same(*page_table, orig_pte))
+			if (!pte_same(*page_table, orig_pte)) {
+				unlock_page(old_page);
+				page_cache_release(old_page);
 				goto unlock;
+			}
 
 			page_mkwrite = 1;
 		}
@@ -2094,9 +2105,6 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 unlock:
 	pte_unmap_unlock(page_table, ptl);
 	if (dirty_page) {
-		if (vma->vm_file)
-			file_update_time(vma->vm_file);
-
 		/*
 		 * Yes, Virginia, this is actually required to prevent a race
 		 * with clear_page_dirty_for_io() from clearing the page dirty
@@ -2105,16 +2113,41 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		 *
 		 * do_no_page is protected similarly.
 		 */
-		wait_on_page_locked(dirty_page);
-		set_page_dirty_balance(dirty_page, page_mkwrite);
+		if (!page_mkwrite) {
+			wait_on_page_locked(dirty_page);
+			set_page_dirty_balance(dirty_page, page_mkwrite);
+		}
 		put_page(dirty_page);
+		if (page_mkwrite) {
+			struct address_space *mapping = dirty_page->mapping;
+
+			set_page_dirty(dirty_page);
+			unlock_page(dirty_page);
+			page_cache_release(dirty_page);
+			if (mapping)	{
+				/*
+				 * Some device drivers do not set page.mapping
+				 * but still dirty their pages
+				 */
+				balance_dirty_pages_ratelimited(mapping);
+			}
+		}
+
+		/* file_update_time outside page_lock */
+		if (vma->vm_file)
+			file_update_time(vma->vm_file);
 	}
 	return ret;
 oom_free_new:
 	page_cache_release(new_page);
 oom:
-	if (old_page)
+	if (old_page) {
+		if (page_mkwrite) {
+			unlock_page(old_page);
+			page_cache_release(old_page);
+		}
 		page_cache_release(old_page);
+	}
 	return VM_FAULT_OOM;
 
 unwritable_page:
@@ -2664,27 +2697,22 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 				int tmp;
 
 				unlock_page(page);
-				vmf.flags |= FAULT_FLAG_MKWRITE;
+				vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
 				tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
 				if (unlikely(tmp &
 					  (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
 					ret = tmp;
-					anon = 1; /* no anon but release vmf.page */
-					goto out_unlocked;
-				}
-				lock_page(page);
-				/*
-				 * XXX: this is not quite right (racy vs
-				 * invalidate) to unlock and relock the page
-				 * like this, however a better fix requires
-				 * reworking page_mkwrite locking API, which
-				 * is better done later.
-				 */
-				if (!page->mapping) {
-					ret = 0;
-					anon = 1; /* no anon but release vmf.page */
-					goto out;
+					goto unwritable_page;
 				}
+				if (unlikely(!(tmp & VM_FAULT_LOCKED))) {
+					lock_page(page);
+					if (!page->mapping) {
+						ret = 0; /* retry the fault */
+						unlock_page(page);
+						goto unwritable_page;
+					}
+				} else
+					VM_BUG_ON(!PageLocked(page));
 				page_mkwrite = 1;
 			}
 		}
@@ -2736,19 +2764,35 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	pte_unmap_unlock(page_table, ptl);
 
 out:
-	unlock_page(vmf.page);
-out_unlocked:
-	if (anon)
-		page_cache_release(vmf.page);
-	else if (dirty_page) {
-		if (vma->vm_file)
-			file_update_time(vma->vm_file);
+	if (dirty_page) {
+		struct address_space *mapping = page->mapping;
 
-		set_page_dirty_balance(dirty_page, page_mkwrite);
+		if (set_page_dirty(dirty_page))
+			page_mkwrite = 1;
+		unlock_page(dirty_page);
 		put_page(dirty_page);
+		if (page_mkwrite && mapping) {
+			/*
+			 * Some device drivers do not set page.mapping but still
+			 * dirty their pages
+			 */
+			balance_dirty_pages_ratelimited(mapping);
+		}
+
+		/* file_update_time outside page_lock */
+		if (vma->vm_file)
+			file_update_time(vma->vm_file);
+	} else {
+		unlock_page(vmf.page);
+		if (anon)
+			page_cache_release(vmf.page);
 	}
 
 	return ret;
+
+unwritable_page:
+	page_cache_release(page);
+	return ret;
 }
 
 static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma,