On Mon 19-06-17 21:05:29, Rasmus Villemoes wrote: > On Mon, Jun 19 2017, Vlastimil Babka <vba...@suse.cz> wrote: > > > On 06/19/2017 03:54 PM, Hao Lee wrote: > >> The variable current_order decreases from MAX_ORDER-1 to order, so the > >> condition current_order <= MAX_ORDER-1 is always true. > >> > >> Signed-off-by: Hao Lee <haolee.sw...@gmail.com> > > > > Sounds right. > > > > Acked-by: Vlastimil Babka <vba...@suse.cz> > > current_order and order are both unsigned, and if order==0, > current_order >= order is always true, and we may decrement > current_order past 0 making it UINT_MAX... A comment would be in order, > though.
Yes, not the first time this has been brought up https://lkml.org/lkml/2016/6/20/493. I guess a comment is long overdue. Or just get rid of the unsigned trap which would be probably more clean. > >> --- > >> mm/page_alloc.c | 5 ++--- > >> 1 file changed, 2 insertions(+), 3 deletions(-) > >> > >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > >> index 2302f25..9120c2b 100644 > >> --- a/mm/page_alloc.c > >> +++ b/mm/page_alloc.c > >> @@ -2215,9 +2215,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int > >> order, int start_migratetype) > >> bool can_steal; > >> > >> /* Find the largest possible block of pages in the other list */ > >> - for (current_order = MAX_ORDER-1; > >> - current_order >= order && current_order <= > >> MAX_ORDER-1; > >> - --current_order) { > >> + for (current_order = MAX_ORDER-1; current_order >= order; > >> + --current_order) { > >> area = &(zone->free_area[current_order]); > >> fallback_mt = find_suitable_fallback(area, current_order, > >> start_migratetype, false, &can_steal); > >> -- Michal Hocko SUSE Labs
