1 files changed, 116 insertions, 12 deletions

diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index a69787e7dd96..1d8332563863 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -40,8 +40,10 @@ static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
 
 	_debug("--- monitor %p %lx ---", page, page->flags);
 
-	if (!PageUptodate(page) && !PageError(page))
-		dump_stack();
+	if (!PageUptodate(page) && !PageError(page)) {
+		/* unlocked, not uptodate and not erronous? */
+		_debug("page probably truncated");
+	}
 
 	/* remove from the waitqueue */
 	list_del(&wait->task_list);
@@ -61,6 +63,84 @@ static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
 }
 
 /*
+ * handle a probably truncated page
+ * - check to see if the page is still relevant and reissue the read if
+ *   possible
+ * - return -EIO on error, -ENODATA if the page is gone, -EINPROGRESS if we
+ *   must wait again and 0 if successful
+ */
+static int cachefiles_read_reissue(struct cachefiles_object *object,
+				   struct cachefiles_one_read *monitor)
+{
+	struct address_space *bmapping = object->backer->d_inode->i_mapping;
+	struct page *backpage = monitor->back_page, *backpage2;
+	int ret;
+
+	kenter("{ino=%lx},{%lx,%lx}",
+	       object->backer->d_inode->i_ino,
+	       backpage->index, backpage->flags);
+
+	/* skip if the page was truncated away completely */
+	if (backpage->mapping != bmapping) {
+		kleave(" = -ENODATA [mapping]");
+		return -ENODATA;
+	}
+
+	backpage2 = find_get_page(bmapping, backpage->index);
+	if (!backpage2) {
+		kleave(" = -ENODATA [gone]");
+		return -ENODATA;
+	}
+
+	if (backpage != backpage2) {
+		put_page(backpage2);
+		kleave(" = -ENODATA [different]");
+		return -ENODATA;
+	}
+
+	/* the page is still there and we already have a ref on it, so we don't
+	 * need a second */
+	put_page(backpage2);
+
+	INIT_LIST_HEAD(&monitor->op_link);
+	add_page_wait_queue(backpage, &monitor->monitor);
+
+	if (trylock_page(backpage)) {
+		ret = -EIO;
+		if (PageError(backpage))
+			goto unlock_discard;
+		ret = 0;
+		if (PageUptodate(backpage))
+			goto unlock_discard;
+
+		kdebug("reissue read");
+		ret = bmapping->a_ops->readpage(NULL, backpage);
+		if (ret < 0)
+			goto unlock_discard;
+	}
+
+	/* but the page may have been read before the monitor was installed, so
+	 * the monitor may miss the event - so we have to ensure that we do get
+	 * one in such a case */
+	if (trylock_page(backpage)) {
+		_debug("jumpstart %p {%lx}", backpage, backpage->flags);
+		unlock_page(backpage);
+	}
+
+	/* it'll reappear on the todo list */
+	kleave(" = -EINPROGRESS");
+	return -EINPROGRESS;
+
+unlock_discard:
+	unlock_page(backpage);
+	spin_lock_irq(&object->work_lock);
+	list_del(&monitor->op_link);
+	spin_unlock_irq(&object->work_lock);
+	kleave(" = %d", ret);
+	return ret;
+}
+
+/*
  * copy data from backing pages to netfs pages to complete a read operation
  * - driven by FS-Cache's thread pool
  */
@@ -92,20 +172,26 @@ static void cachefiles_read_copier(struct fscache_operation *_op)
 
 		_debug("- copy {%lu}", monitor->back_page->index);
 
-		error = -EIO;
+	recheck:
 		if (PageUptodate(monitor->back_page)) {
 			copy_highpage(monitor->netfs_page, monitor->back_page);
 
 			pagevec_add(&pagevec, monitor->netfs_page);
 			fscache_mark_pages_cached(monitor->op, &pagevec);
 			error = 0;
-		}
-
-		if (error)
+		} else if (!PageError(monitor->back_page)) {
+			/* the page has probably been truncated */
+			error = cachefiles_read_reissue(object, monitor);
+			if (error == -EINPROGRESS)
+				goto next;
+			goto recheck;
+		} else {
 			cachefiles_io_error_obj(
 				object,
 				"Readpage failed on backing file %lx",
 				(unsigned long) monitor->back_page->flags);
+			error = -EIO;
+		}
 
 		page_cache_release(monitor->back_page);
 
@@ -114,6 +200,7 @@ static void cachefiles_read_copier(struct fscache_operation *_op)
 		fscache_put_retrieval(op);
 		kfree(monitor);
 
+	next:
 		/* let the thread pool have some air occasionally */
 		max--;
 		if (max < 0 || need_resched()) {
@@ -333,7 +420,8 @@ int cachefiles_read_or_alloc_page(struct fscache_retrieval *op,
 
 	shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
 
-	op->op.flags = FSCACHE_OP_FAST;
+	op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
+	op->op.flags |= FSCACHE_OP_FAST;
 	op->op.processor = cachefiles_read_copier;
 
 	pagevec_init(&pagevec, 0);
@@ -639,7 +727,8 @@ int cachefiles_read_or_alloc_pages(struct fscache_retrieval *op,
 
 	pagevec_init(&pagevec, 0);
 
-	op->op.flags = FSCACHE_OP_FAST;
+	op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
+	op->op.flags |= FSCACHE_OP_FAST;
 	op->op.processor = cachefiles_read_copier;
 
 	INIT_LIST_HEAD(&backpages);
@@ -801,7 +890,8 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page)
 	struct cachefiles_cache *cache;
 	mm_segment_t old_fs;
 	struct file *file;
-	loff_t pos;
+	loff_t pos, eof;
+	size_t len;
 	void *data;
 	int ret;
 
@@ -835,15 +925,29 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page)
 		ret = -EIO;
 		if (file->f_op->write) {
 			pos = (loff_t) page->index << PAGE_SHIFT;
+
+			/* we mustn't write more data than we have, so we have
+			 * to beware of a partial page at EOF */
+			eof = object->fscache.store_limit_l;
+			len = PAGE_SIZE;
+			if (eof & ~PAGE_MASK) {
+				ASSERTCMP(pos, <, eof);
+				if (eof - pos < PAGE_SIZE) {
+					_debug("cut short %llx to %llx",
+					       pos, eof);
+					len = eof - pos;
+					ASSERTCMP(pos + len, ==, eof);
+				}
+			}
+
 			data = kmap(page);
 			old_fs = get_fs();
 			set_fs(KERNEL_DS);
 			ret = file->f_op->write(
-				file, (const void __user *) data, PAGE_SIZE,
-				&pos);
+				file, (const void __user *) data, len, &pos);
 			set_fs(old_fs);
 			kunmap(page);
-			if (ret != PAGE_SIZE)
+			if (ret != len)
 				ret = -EIO;
 		}
 		fput(file);