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SubjectRe: [PATCH v3] virtio-balloon: fix managed page counts when migrating pages between zones
On Wed, Dec 11, 2019 at 12:11:52PM +0100, David Hildenbrand wrote:
> 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 online 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 if
> the zone changed. 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).
>
> We'll temporarily modify the totalram page count. If this ever becomes a
> problem, we can fine tune by providing helpers that don't touch
> the totalram pages (e.g., adjust_zone_managed_page_count()).
>
> Please note that fixing up the managed page count is only necessary when
> we adjusted the managed page count when inflating - only if we
> don't have VIRTIO_BALLOON_F_DEFLATE_ON_OOM. With that feature, the
> managed page count is not touched when inflating/deflating.
>
> Reported-by: Yumei Huang <yuhuang@redhat.com>
> Fixes: 3dcc0571cd64 ("mm: correctly update zone->managed_pages")
> Cc: <stable@vger.kernel.org> # v3.11+
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: Jiang Liu <liuj97@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: virtualization@lists.linux-foundation.org
> Signed-off-by: David Hildenbrand <david@redhat.com>

Looks good, will queue this up, thanks!

> ---
>
> v2 -> v3:
> - Refine comment
> - s/only/online/ in description
> - Clarify why VIRTIO_BALLOON_F_DEFLATE_ON_OOM has to be checked
>
> v1 -> v2:
> - Adjust count before enquing newpage (and it possibly gets free form the
> balloon)
> - Check if the zone changed
>
> ---
> drivers/virtio/virtio_balloon.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 15b7f1d8c334..93f995f6cf36 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -722,6 +722,17 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
>
> get_page(newpage); /* balloon reference */
>
> + /*
> + * When we migrate a page to a different zone and adjusted the
> + * managed page count when inflating, we have to fixup the count of
> + * both involved zones.
> + */
> + if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM) &&
> + page_zone(page) != page_zone(newpage)) {
> + adjust_managed_page_count(page, 1);
> + adjust_managed_page_count(newpage, -1);
> + }
> +
> /* balloon's page migration 1st step -- inflate "newpage" */
> spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
> balloon_page_insert(vb_dev_info, newpage);
> --
> 2.23.0

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