After upgrading to PHP 7 I started getting "storage folder isn't writable by PHP" errors I just recently upgraded to PHP 7. The browser is now showing following error

/home/xxx/craft/storage isn't writable by PHP. Please fix that


Have not changed any permissions on any of the folders. How to fix this problem?
Try resetting the permissions of the storage folder:

https://craftcms.com/docs/installing#step-2-set-the-permissions

(It's possible that PHP was running with higher-than-default permissions in the previous setup, in which case everything may have worked even if you hadn't explicitly made the storage folder writable.)