mm, something wring in page_lock_anon_vma_read()?

[Xishi Qiu]

Hi, my system triggers this bug, and the vmcore shows the anon_vma seems be freed.
The kernel is RHEL 7.2, and the bug is hard to reproduce, so I don't know if it
exists in mainline, any reply is welcome!

[35030.332666] general protection fault: 0000 [#1] SMP
[35030.333016] Modules linked in: veth ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 xt_addrtype iptable_filter xt_conntrack nf_nat nf_conntrack bridge stp llc dm_thin_pool dm_persistent_data dm_bio_prison dm_bufio libcrc32c rtos_kbox_panic(OE) ipmi_devintf ipmi_si ipmi_msghandler signo_catch(O) cirrus syscopyarea sysfillrect sysimgblt ttm crc32_pclmul ghash_clmulni_intel drm_kms_helper aesni_intel ppdev drm lrw gf128mul parport_pc glue_helper ablk_helper serio_raw cryptd i2c_piix4 parport pcspkr sg floppy i2c_core dm_mod sha512_generic ip_tables sd_mod crc_t10dif crct10dif_generic sr_mod cdrom virtio_console virtio_scsi virtio_net ata_generic pata_acpi crct10dif_pclmul crct10dif_common crc32c_intel virtio_pci virtio_ring virtio ata_piix libata ext4 mbcache
[35030.333016]  jbd2
[35030.333016] CPU: 3 PID: 48 Comm: kswapd0 Tainted: G           OE  ---- -------   3.10.0-327.36.58.4.x86_64 #1
[35030.333016] Hardware name: OpenStack Foundation OpenStack Nova, BIOS rel-1.8.1-0-g4adadbd-20160826_044443-hghoulaslx112 04/01/2014
[35030.333016] task: ffff8801b2d20000 ti: ffff8801b4c38000 task.ti: ffff8801b4c38000
[35030.333016] RIP: 0010:[<ffffffff810acac5>]  [<ffffffff810acac5>] down_read_trylock+0x5/0x50
[35030.333016] RSP: 0000:ffff8801b4c3ba90  EFLAGS: 00010282
[35030.333016] RAX: 0000000000000000 RBX: ffff8801b3e2a100 RCX: 0000000000000000
[35030.333016] RDX: 0000000000000000 RSI: 0000000000000000 RDI: deb604d497705c5d
[35030.333016] RBP: ffff8801b4c3bab8 R08: ffffea0002c34460 R09: ffff8801b3d7e8a0
[35030.333016] R10: 0000000000000004 R11: fff00000fe000000 R12: ffff8801b3e2a101
[35030.333016] R13: ffffea0002c34440 R14: deb604d497705c5d R15: ffffea0002c34440
[35030.333016] FS:  0000000000000000(0000) GS:ffff8801bed80000(0000) knlGS:0000000000000000
[35030.333016] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[35030.333016] CR2: 000000c422011080 CR3: 0000000001976000 CR4: 00000000001407e0
[35030.333016] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[35030.333016] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[35030.333016] Stack:
[35030.333016]  ffffffff811b2795 ffffea0002c34440 0000000000000000 000000000000000f
[35030.333016]  0000000000000001 ffff8801b4c3bb30 ffffffff811b2a17 ffff8800a712d640
[35030.333016]  000000000c4229e2 ffff8801b4c3bb80 0000000100000000 000000000c41fe38
[35030.333016] Call Trace:
[35030.333016]  [<ffffffff811b2795>] ? page_lock_anon_vma_read+0x55/0x110
[35030.333016]  [<ffffffff811b2a17>] page_referenced+0x1c7/0x350
[35030.333016]  [<ffffffff8118d9b4>] shrink_active_list+0x1e4/0x400
[35030.333016]  [<ffffffff8118e08d>] shrink_lruvec+0x4bd/0x770
[35030.333016]  [<ffffffff8118e3b6>] shrink_zone+0x76/0x1a0
[35030.333016]  [<ffffffff8118f6cc>] balance_pgdat+0x49c/0x610
[35030.333016]  [<ffffffff8118f9b3>] kswapd+0x173/0x450
[35030.333016]  [<ffffffff810a8a00>] ? wake_up_atomic_t+0x30/0x30
[35030.333016]  [<ffffffff8118f840>] ? balance_pgdat+0x610/0x610
[35030.333016]  [<ffffffff810a79bf>] kthread+0xcf/0xe0
[35030.333016]  [<ffffffff810a78f0>] ? kthread_create_on_node+0x120/0x120
[35030.333016]  [<ffffffff81665bd8>] ret_from_fork+0x58/0x90
[35030.333016]  [<ffffffff810a78f0>] ? kthread_create_on_node+0x120/0x120
[35030.333016] Code: 00 ba ff ff ff ff 48 89 d8 f0 48 0f c1 10 79 05 e8 31 06 27 00 5b 5d c3 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 <48> 8b 07 48 89 c2 48 83 c2 01 7e 07 f0 48 0f b1 17 75 f0 48 f7
[35030.333016] RIP  [<ffffffff810acac5>] down_read_trylock+0x5/0x50
[35030.333016]  RSP <ffff8801b4c3ba90>
[35030.333016] ------------[ cut here ]------------

struct page {
  flags = 9007194960298056,
  mapping = 0xffff8801b3e2a101,
  {
    {
      index = 34324593617,
      freelist = 0x7fde7bbd1,
      pfmemalloc = 209,
      thp_mmu_gather = {
        counter = -35144751
      },
      pmd_huge_pte = 0x7fde7bbd1
    },
    {
      counters = 8589934592,
      {
        {
          _mapcount = {
            counter = 0
          },
          {
            inuse = 0,
            objects = 0,
            frozen = 0
          },
          units = 0
        },
        _count = {
          counter = 2
        }
      }
    }
  },
  {
    lru = {
      next = 0xdead000000100100,
      prev = 0xdead000000200200
    },
    {
      next = 0xdead000000100100,
      pages = 2097664,
      pobjects = -559087616
    },
    list = {
      next = 0xdead000000100100,
      prev = 0xdead000000200200
    },
    slab_page = 0xdead000000100100
  },
  {
    private = 0,
    ptl = {
      {
        rlock = {
          raw_lock = {
            {
              head_tail = 0,
              tickets = {
                head = 0,
                tail = 0
              }
            }
          }
        }
      }
    },
    slab_cache = 0x0,
    first_page = 0x0
  }
}



crash> struct anon_vma 0xffff8801b3e2a100
struct anon_vma {
  root = 0xdeb604d497705c55,
  rwsem = {
    count = -8192007903225070328,
    wait_lock = {
      raw_lock = {
        {
          head_tail = 2955503940,
          tickets = {
            head = 26948,
            tail = 45097
          }
        }
      }
    },
    wait_list = {
      next = 0x559f9107c1b47439,
      prev = 0x3de13f709bfa043b
    }
  },
  refcount = {
    counter = -13243516
  },
  rb_root = {
    rb_node = 0x11dd18f9ce0bb2e9
  }
}

This address 0xffff8801b3e2a100 can not find in "kmem -S anon_vma"

The page flags is
crash> kmem -g 0x1FFFFF00080048
FLAGS: 1fffff00080048
  PAGE-FLAG        BIT  VALUE
  PG_uptodate        3  0000008
  PG_active          6  0000040
  PG_swapbacked     19  0080000