block: Don't invalidate pagecache for invalid falloc modes

Only call truncate_bdev_range() if the fallocate mode is
supported. This fixes a bug where data in the pagecache
could be invalidated if the fallocate() was called on the
block device with an invalid mode.

Fixes: 25f4c41 ("block: implement (some of) fallocate for block devices")
Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>

block/fops.c

@@ -648,25 +648,27 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 
 	filemap_invalidate_lock(inode->i_mapping);
 
-	/* Invalidate the page cache, including dirty pages. */
-	error = truncate_bdev_range(bdev, file->f_mode, start, end);
-	if (error)
-		goto fail;
-
+	/*
+	 * Invalidate the page cache, including dirty pages, for valid
+	 * de-allocate mode calls to fallocate().
+	 */
 	switch (mode) {
 	case FALLOC_FL_ZERO_RANGE:
 	case FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE:
-		error = blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
+		error = truncate_bdev_range(bdev, file->f_mode, start, end) ||
+			blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
 					     len >> SECTOR_SHIFT, GFP_KERNEL,
 					     BLKDEV_ZERO_NOUNMAP);
 		break;
 	case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE:
-		error = blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
+		error = truncate_bdev_range(bdev, file->f_mode, start, end) ||
+			blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
 					     len >> SECTOR_SHIFT, GFP_KERNEL,
 					     BLKDEV_ZERO_NOFALLBACK);
 		break;
 	case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE | FALLOC_FL_NO_HIDE_STALE:
-		error = blkdev_issue_discard(bdev, start >> SECTOR_SHIFT,
+		error = truncate_bdev_range(bdev, file->f_mode, start, end) ||
+			blkdev_issue_discard(bdev, start >> SECTOR_SHIFT,
 					     len >> SECTOR_SHIFT, GFP_KERNEL);
 		break;
 	default: