Free swap negative?

[Laura Abbott <labbott@redhat.com>]

Hi,

Fedora got a bug report of an OOM which listed a negative number of swap
pages on 4.16-rc4

[ 2201.781891] localhost-live kernel: Free swap  = -245804kB
[ 2201.781892] localhost-live kernel: Total swap = 0kB
[ 2201.781894] localhost-live kernel: 458615 pages RAM

The setup itself was unusual, virt with 1792M RAM + 2G swap.
This apparently used to work but the test case was installation
media which is a bit painful to bisect. Full oom output is below:

  anaconda invoked oom-killer: gfp_mask=0x14200ca(GFP_HIGHUSER_MOVABLE), nodemask=(null), order=0, oom_score_adj=0
  anaconda cpuset=/ mems_allowed=0
  CPU: 1 PID: 4928 Comm: anaconda Not tainted 4.16.0-0.rc4.git0.1.fc28.x86_64 #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-2.fc27 04/01/2014
  Call Trace:
   dump_stack+0x5c/0x85
   dump_header+0x6e/0x275
   oom_kill_process.cold.28+0xb/0x3c9
   oom_badness+0xe1/0x160
   ? out_of_memory+0x1ca/0x4c0
   ? __alloc_pages_slowpath+0xca5/0xd80
   ? __alloc_pages_nodemask+0x28e/0x2b0
   ? alloc_pages_vma+0x74/0x1e0
   ? __read_swap_cache_async+0x14c/0x220
   ? read_swap_cache_async+0x28/0x60
   ? try_to_unuse+0x135/0x760
   ? swapcache_free_entries+0x11d/0x180
   ? drain_slots_cache_cpu.constprop.1+0x8a/0xd0
   ? SyS_swapoff+0x1d6/0x6b0
   ? do_syscall_64+0x74/0x180
   ? entry_SYSCALL_64_after_hwframe+0x3d/0xa2
  Mem-Info:
  active_anon:98024 inactive_anon:167006 isolated_anon:0
             active_file:138 inactive_file:226 isolated_file:0
             unevictable:118208 dirty:0 writeback:0 unstable:0
             slab_reclaimable:7506 slab_unreclaimable:18839
             mapped:1889 shmem:2744 pagetables:10605 bounce:0
             free:12856 free_pcp:235 free_cma:0
  Node 0 active_anon:392096kB inactive_anon:668024kB active_file:552kB inactive_file:904kB unevictable:472832kB isolated(anon):0kB isolated(file):0kB mapped:7556kB dirty:0kB writeback:0kB shmem:10976kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
  Node 0 DMA free:7088kB min:412kB low:512kB high:612kB active_anon:2428kB inactive_anon:3120kB active_file:0kB inactive_file:0kB unevictable:2428kB writepending:0kB present:15992kB managed:15908kB mlocked:0kB kernel_stack:0kB pagetables:40kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
  lowmem_reserve[]: 0 1670 1670 1670 1670
  Node 0 DMA32 free:44336kB min:44640kB low:55800kB high:66960kB active_anon:389668kB inactive_anon:664904kB active_file:552kB inactive_file:984kB unevictable:470404kB writepending:0kB present:1818468kB managed:1766292kB mlocked:16kB kernel_stack:7840kB pagetables:42380kB bounce:0kB free_pcp:940kB local_pcp:736kB free_cma:0kB
  lowmem_reserve[]: 0 0 0 0 0
  Node 0 DMA: 6*4kB (UME) 19*8kB (UME) 12*16kB (UE) 4*32kB (UE) 29*64kB (ME) 11*128kB (UME) 3*256kB (ME) 3*512kB (UME) 1*1024kB (M) 0*2048kB 0*4096kB = 7088kB
  Node 0 DMA32: 986*4kB (UMEH) 815*8kB (UMEH) 359*16kB (UMEH) 113*32kB (UMEH) 229*64kB (UMEH) 51*128kB (UMEH) 7*256kB (UMEH) 3*512kB (ME) 0*1024kB 0*2048kB 0*4096kB = 44336kB
  Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
  122508 total pagecache pages
  1176 pages in swap cache
  Swap cache stats: add 222119, delete 220943, find 18522/25378
  Free swap  = -245804kB
  Total swap = 0kB
  458615 pages RAM
  0 pages HighMem/MovableOnly
  13065 pages reserved
  0 pages cma reserved
  0 pages hwpoisoned

Any suggestions?

Thanks,
Laura