On Fri, Jan 24, 2020 at 03:46:43PM +0100, Michal Hocko wrote: >On Fri 24-01-20 22:15:38, Wei Yang wrote: >> On Fri, Jan 24, 2020 at 08:21:27AM +0100, Michal Hocko wrote: >> >[Sorry I have missed this patch previously] >> > >> >> No problem, thanks for your comment. >> >> >On Sun 19-01-20 14:57:53, Wei Yang wrote: >> >> If we get here after successfully adding page to list, err would be >> >> 1 to indicate the page is queued in the list. >> >> >> >> Current code has two problems: >> >> >> >> * on success, 0 is not returned >> >> * on error, if add_page_for_migratioin() return 1, and the following err1 >> >> from do_move_pages_to_node() is set, the err1 is not returned since err >> >> is 1 >> > >> >This made my really scratch my head to grasp. So essentially err > 0 >> >will happen when we reach the end of the loop and rely on the >> >out_flush flushing to migrate the batch. Then err contains the >> >add_page_for_migratioin return value. And that would leak to the >> >userspace. >> > >> >What would you say about the following wording instead? >> >" >> >out_flush part of do_pages_move is responsible for migrating the last >> >batch that accumulated while processing the input in the loop. >> >do_move_pages_to_node return value is supposed to override any >> >preexisting error (e.g. when the user input is garbage) but the current >> >> I am afraid I have a different understanding here. >> >> If we jump to out_flush on the test of node_isset(), err is -EACCESS. Current >> logic would return this instead of the error from do_move_pages_to_node(). >> Seems we don't override -EACCESS. > >And this is the expected logic. The unexpected behavior is the one you >have fixed by this patch because err = 1 wouldn't get overriden and that >should have been. Ok, if the sentence cover this case, the wording looks good to me. Thanks :-) >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me
