> so an error on the 1st page gets propagated to the caller, > and that get_user_pages_unlocked eventually calls __get_user_pages > so it does return an error sometimes. > > Would it be correct to apply the second part of the patch then > (pasted below for reference) or should get_user_pages_fast > and all its callers be changed to return 0 on error instead? 0 isn't an error. As SuS sees it (ie from the userspace end of the pile) returning the number you asked for means it worked returning a smaller number means it worked partially and that much was consumed (or in some cases more and the rest if so was lost - depends what you are reading/writing) returning 0 means you read nothing as you were at the end of file returning an error code means it broke, or you should try again (EAGAIN/EWOULDBLOCK) The ugly bit there is the try-again semantics needs to exactly match the attached poll() behaviour or you get busy loops. Alan