From: Wei Yang richard.weiyang@gmail.com
[ Upstream commit 8f416836c0d50b198cad1225132e5abebf8980dc ]
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@gmail.com Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") Signed-off-by: Wei Yang richard.weiyang@gmail.com Acked-by: Michal Hocko mhocko@suse.com Reviewed-by: Oscar Salvador osalvador@suse.de Cc: Anshuman Khandual anshuman.khandual@arm.com Cc: Dave Hansen dave.hansen@intel.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org
Signed-off-by: Sasha Levin sashal@kernel.org --- mm/page_alloc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index b721631d78ab..6a62b2421cdf 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5733,8 +5733,10 @@ void __meminit init_currently_empty_zone(struct zone *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;