[PATCH] virtio-balloon: fix managed page counts when migrating pages between zones

From: David Hildenbrand
Date: Wed Dec 04 2019 - 15:48:22 EST

In case we have to migrate a ballon page to a newpage of another zone, the
managed page count of both zones is wrong. Paired with memory offlining
(which will adjust the managed page count), we can trigger kernel crashes
and all kinds of different symptoms.

One way to reproduce:
1. Start a QEMU guest with 4GB, no NUMA
2. Hotplug a 1GB DIMM and only the memory to ZONE_NORMAL
3. Inflate the balloon to 1GB
4. Unplug the DIMM (be quick, otherwise unmovable data ends up on it)
5. Observe /proc/zoneinfo
Node 0, zone Normal
pages free 16810
min 24848885473806
low 18471592959183339
high 36918337032892872
spanned 262144
present 262144
managed 18446744073709533486
6. Do anything that requires some memory (e.g., inflate the balloon some
more). The OOM goes crazy and the system crashes
[ 238.324946] Out of memory: Killed process 537 (login) total-vm:27584kB, anon-rss:860kB, file-rss:0kB, shmem-rss:00
[ 238.338585] systemd invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0, oom_score_adj=0
[ 238.339420] CPU: 0 PID: 1 Comm: systemd Tainted: G D W 5.4.0-next-20191204+ #75
[ 238.340139] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu4
[ 238.341121] Call Trace:
[ 238.341337] dump_stack+0x8f/0xd0
[ 238.341630] dump_header+0x61/0x5ea
[ 238.341942] oom_kill_process.cold+0xb/0x10
[ 238.342299] out_of_memory+0x24d/0x5a0
[ 238.342625] __alloc_pages_slowpath+0xd12/0x1020
[ 238.343024] __alloc_pages_nodemask+0x391/0x410
[ 238.343407] pagecache_get_page+0xc3/0x3a0
[ 238.343757] filemap_fault+0x804/0xc30
[ 238.344083] ? ext4_filemap_fault+0x28/0x42
[ 238.344444] ext4_filemap_fault+0x30/0x42
[ 238.344789] __do_fault+0x37/0x1a0
[ 238.345087] __handle_mm_fault+0x104d/0x1ab0
[ 238.345450] handle_mm_fault+0x169/0x360
[ 238.345790] do_user_addr_fault+0x20d/0x490
[ 238.346154] do_page_fault+0x31/0x210
[ 238.346468] async_page_fault+0x43/0x50
[ 238.346797] RIP: 0033:0x7f47eba4197e
[ 238.347110] Code: Bad RIP value.
[ 238.347387] RSP: 002b:00007ffd7c0c1890 EFLAGS: 00010293
[ 238.347834] RAX: 0000000000000002 RBX: 000055d196a20a20 RCX: 00007f47eba4197e
[ 238.348437] RDX: 0000000000000033 RSI: 00007ffd7c0c18c0 RDI: 0000000000000004
[ 238.349047] RBP: 00007ffd7c0c1c20 R08: 0000000000000000 R09: 0000000000000033
[ 238.349660] R10: 00000000ffffffff R11: 0000000000000293 R12: 0000000000000001
[ 238.350261] R13: ffffffffffffffff R14: 0000000000000000 R15: 00007ffd7c0c18c0
[ 238.350878] Mem-Info:
[ 238.351085] active_anon:3121 inactive_anon:51 isolated_anon:0
[ 238.351085] active_file:12 inactive_file:7 isolated_file:0
[ 238.351085] unevictable:0 dirty:0 writeback:0 unstable:0
[ 238.351085] slab_reclaimable:5565 slab_unreclaimable:10170
[ 238.351085] mapped:3 shmem:111 pagetables:155 bounce:0
[ 238.351085] free:720717 free_pcp:2 free_cma:0
[ 238.353757] Node 0 active_anon:12484kB inactive_anon:204kB active_file:48kB inactive_file:28kB unevictable:0kB iss
[ 238.355979] Node 0 DMA free:11556kB min:36kB low:48kB high:60kB reserved_highatomic:0KB active_anon:152kB inactivB
[ 238.358345] lowmem_reserve[]: 0 2955 2884 2884 2884
[ 238.358761] Node 0 DMA32 free:2677864kB min:7004kB low:10028kB high:13052kB reserved_highatomic:0KB active_anon:0B
[ 238.361202] lowmem_reserve[]: 0 0 72057594037927865 72057594037927865 72057594037927865
[ 238.361888] Node 0 Normal free:193448kB min:99395541895224kB low:73886371836733356kB high:147673348131571488kB reB
[ 238.364765] lowmem_reserve[]: 0 0 0 0 0
[ 238.365101] Node 0 DMA: 7*4kB (U) 5*8kB (UE) 6*16kB (UME) 2*32kB (UM) 1*64kB (U) 2*128kB (UE) 3*256kB (UME) 2*512B
[ 238.366379] Node 0 DMA32: 0*4kB 1*8kB (U) 2*16kB (UM) 2*32kB (UM) 2*64kB (UM) 1*128kB (U) 1*256kB (U) 1*512kB (U)B
[ 238.367654] Node 0 Normal: 1985*4kB (UME) 1321*8kB (UME) 844*16kB (UME) 524*32kB (UME) 300*64kB (UME) 138*128kB (B
[ 238.369184] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[ 238.369915] 130 total pagecache pages
[ 238.370241] 0 pages in swap cache
[ 238.370533] Swap cache stats: add 0, delete 0, find 0/0
[ 238.370981] Free swap = 0kB
[ 238.371239] Total swap = 0kB
[ 238.371488] 1048445 pages RAM
[ 238.371756] 0 pages HighMem/MovableOnly
[ 238.372090] 306992 pages reserved
[ 238.372376] 0 pages cma reserved
[ 238.372661] 0 pages hwpoisoned

In another instance (older kernel), I was able to observe this
(negative page count :/):
[ 180.896971] Offlined Pages 32768
[ 182.667462] Offlined Pages 32768
[ 184.408117] Offlined Pages 32768
[ 186.026321] Offlined Pages 32768
[ 187.684861] Offlined Pages 32768
[ 189.227013] Offlined Pages 32768
[ 190.830303] Offlined Pages 32768
[ 190.833071] Built 1 zonelists, mobility grouping on. Total pages: -36920272750453009

In another instance (older kernel), I was no longer able to start any
process:
[root@vm ~]# [ 214.348068] Offlined Pages 32768
[ 215.973009] Offlined Pages 32768
cat /proc/meminfo
-bash: fork: Cannot allocate memory
[root@vm ~]# cat /proc/meminfo
-bash: fork: Cannot allocate memory

Fix it by properly adjusting the managed page count when migrating. The
managed page count of the zones now looks after unplug of the DIMM
(and after deflating the balloon) just like before inflating the balloon
(and plugging+onlining the DIMM).

Reported-by: Yumei Huang <yuhuang@xxxxxxxxxx>
Fixes: 3dcc0571cd64 ("mm: correctly update zone->managed_pages")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.11+
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Jiang Liu <liuj97@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
drivers/virtio/virtio_balloon.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 15b7f1d8c334..1089b07679cf 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -742,6 +742,12 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,

mutex_unlock(&vb->balloon_lock);

+ /* fixup the managed page count (esp. of the zone) */
+ if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
+ adjust_managed_page_count(page, 1);
+ adjust_managed_page_count(newpage, -1);
+ }
+
put_page(page); /* balloon reference */

return MIGRATEPAGE_SUCCESS;
--
2.21.0