From: Wei Yang <richard.weiyang@xxxxxxxxx> Subject: mm/page_alloc.c: fix calculation of pgdat->nr_zones init_currently_empty_zone() will adjust pgdat->nr_zones and set it to 'zone_idx(zone) + 1' unconditionally. This is correct in the normal case, while not exact in hot-plug situation. This function is used in two places: * free_area_init_core() * move_pfn_range_to_zone() In the first case, we are sure zone index increase monotonically. While in the second one, this is under users control. One way to reproduce this is: ---------------------------- 1. create a virtual machine with empty node1 -m 4G,slots=32,maxmem=32G \ -smp 4,maxcpus=8 \ -numa node,nodeid=0,mem=4G,cpus=0-3 \ -numa node,nodeid=1,mem=0G,cpus=4-7 2. hot-add cpu 3-7 cpu-add [3-7] 2. hot-add memory to nod1 object_add memory-backend-ram,id=ram0,size=1G device_add pc-dimm,id=dimm0,memdev=ram0,node=1 3. online memory with following order echo online_movable > memory47/state echo online > memory40/state After this, node1 will have its nr_zones equals to (ZONE_NORMAL + 1) instead of (ZONE_MOVABLE + 1). Michal said: : Having an incorrect nr_zones might result in all sorts of problems which : would be quite hard to debug (e.g. reclaim not considering the movable : zone). I do not expect many users would suffer from this it but still : this is trivial and obviously right thing to do so backporting to the : stable tree shouldn't be harmful (last famous words). Link: http://lkml.kernel.org/r/20181117022022.9956-1-richard.weiyang@xxxxxxxxx Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_alloc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/mm/page_alloc.c~mm-page_alloc-fix-calculation-of-pgdat-nr_zones +++ a/mm/page_alloc.c @@ -5813,8 +5813,10 @@ void __meminit init_currently_empty_zone unsigned long size) { struct pglist_data *pgdat = zone->zone_pgdat; + int zone_idx = zone_idx(zone) + 1; - pgdat->nr_zones = zone_idx(zone) + 1; + if (zone_idx > pgdat->nr_zones) + pgdat->nr_zones = zone_idx; zone->zone_start_pfn = zone_start_pfn; _
