On Fri, Apr 06, 2018 at 01:08:02PM -0700, Andrew Morton wrote: > On Fri, 6 Apr 2018 00:03:48 +0300 "Michael S. Tsirkin" <m...@redhat.com> > wrote: > > > Turns out get_user_pages_fast and __get_user_pages_fast return different > > values on error when given a single page: __get_user_pages_fast returns > > 0. get_user_pages_fast returns either 0 or an error. > > > > Callers of get_user_pages_fast expect an error so fix it up to return an > > error consistently. > > > > Stress the difference between get_user_pages_fast and __get_user_pages_fast > > to make sure callers aren't confused. > > > > A term which is missing from all these changelogs is "vhost" :(
vhost has a BUG_ON for unexpected handling so it catches the bug, but it's not the only site affected. > This patchset fixes a user-affecting bug, does it not? If so, please > fully describe that bug so that we can decide which kernel version(s) > need the patchset. OK, I'll try to write up something. > And yes, this return value asymmetry is sad. Did you scope out what > would be needed to fix up the callers so we can avoid this? Yes - there is a very small number of callers for __get_user_pages_fast so it's easy to teach them all to treat any value <=0 as 0. There seems to be some opposition to changing the API, I'd like to look into this after the bugfix patchset is merged. -- MST
