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SubjectRe: mm, something wring in page_lock_anon_vma_read()?
On 2017/5/18 17:46, Xishi Qiu wrote:

> 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!
>

When we alloc anon_vma, we will init the value of anon_vma->root,
so can we set anon_vma->root to NULL when calling
anon_vma_free -> kmem_cache_free(anon_vma_cachep, anon_vma);

anon_vma_free()
...
anon_vma->root = NULL;
kmem_cache_free(anon_vma_cachep, anon_vma);

I find if we do this above, system boot failed, why?

Thanks,
Xishi Qiu

> [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
>
>
> .
>



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