如何使用crash分析vmcore - 之基础思路case1

dmesg查看内核日志

[2493382.671020] systemd-shutdown[1]: Sending SIGKILL to PID 28975 (docker-containe).

[2493382.671078] systemd-shutdown[1]: Sending SIGKILL to PID 29015 (systemd).

[2493420.208723] EXT4-fs (nvme0n1p1): sb orphan head is 140906170

[2493420.209198] sb_info orphan list:

[2493420.209663]   inode nvme0n1p1:140906170 at ffff88490edabfb8: mode 100666, nlink 0, next 149423507

[2493420.210129]   inode nvme0n1p1:149423507 at ffff8801b99391a8: mode 100666, nlink 0, next 17567381

[2493420.210583]   inode nvme0n1p1:17567381 at ffff8806d4a26998: mode 100744, nlink 0, next 17570510

[2493420.211050]   inode nvme0n1p1:17570510 at ffff886387f82ef8: mode 100644, nlink 0, next 17570503

[2493420.211508]   inode nvme0n1p1:17570503 at ffff886a1f15bfb8: mode 100644, nlink 0, next 241700498

[2493420.211966]   inode nvme0n1p1:241700498 at ffff8877481800e8: mode 100644, nlink 0, next 243138756

[2493420.212431]   inode nvme0n1p1:243138756 at ffff88761ad10518: mode 100644, nlink 0, next 241565954

[2493420.212900]   inode nvme0n1p1:241565954 at ffff8870d64bbfb8: mode 100755, nlink 0, next 241566333

[2493420.213366]   inode nvme0n1p1:241566333 at ffff88721ae74c48: mode 100644, nlink 0, next 241050093

[2493420.213833]   inode nvme0n1p1:241050093 at ffff887704958948: mode 100755, nlink 0, next 241567324

[2493420.214545] ------------[ cut here ]------------

[2493420.219336] kernel BUG at fs/ext4/super.c:879!  <<<======这里指明BUG的代码位置

[2493420.223948] invalid opcode: 0000 [#1] SMP

[2493420.228133] Modules linked in: kpatch_D751550(OE) kpatch_D631237(OE) unix_diag(E) af_packet_diag(E) netlink_diag(E) dccp_diag(E) dccp(E) tcp_diag(E) udp_diag(E) inet_diag(E) [last unloaded: aisqos_hotfixes]

[2493420.246846] CPU: 58 PID: 1 Comm: systemd-shutdow Tainted: G        W  OE K 4.9.79-009.ali3000.alios7.x86_64 #1

[2493420.257009] Hardware name: Inventec     AliServer Thor01-2U             /TB800G4-G1      , BIOS A1.20 03/06/2018

[2493420.267339] task: ffff887e45918000 task.stack: ffffc90000014000

[2493420.273425] RIP: 0010:[<ffffffffa031a8df>]  [<ffffffffa031a8df>] ext4_put_super+0x36f/0x3c0 [ext4]  <<<=======这里指明BUG的代码位置

[2493420.282593] RSP: 0018:ffffc90000017de8  EFLAGS: 00010206

[2493420.288079] RAX: ffff88490edabf50 RBX: ffff887e43299000 RCX: 00000001949b336d

[2493420.295384] RDX: 0000000000000000 RSI: 0000000000000206 RDI: 0000000000000206

[2493420.302682] RBP: ffffc90000017e18 R08: 00000000000081a4 R09: 0000000000000000

[2493420.309988] R10: 0000000000000cb8 R11: 0000000000001e92 R12: ffff887e43299278

[2493420.317293] R13: ffff887e43298800 R14: ffff887e43299278 R15: ffffffffa034ff88

[2493420.324598] FS:  00007f3241ccf840(0000) GS:ffff887e78480000(0000) knlGS:0000000000000000

[2493420.332850] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033

[2493420.338767] CR2: 00007f5e1372fbd0 CR3: 00000004daa52000 CR4: 00000000007606f0

[2493420.346065] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

[2493420.353361] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

[2493420.360660] PKRU: 55555554

[2493420.363536] Stack:

[2493420.365721]  9cbae75a00000000 ffff887e43298800 ffffffffa034a5e0 ffff887e3818c7b8

[2493420.373365]  0000000000000000 ffff887e45918bb0 ffffc90000017e38 ffffffff81244aaf

[2493420.380991]  0000000000000083 ffff887e357b8680 ffffc90000017e58 ffffffff81244e37

[2493420.388617] Call Trace:

[2493420.391239]  [<ffffffff81244aaf>] generic_shutdown_super+0x6f/0x100

[2493420.397676]  [<ffffffff81244e37>] kill_block_super+0x27/0x70

[2493420.403508]  [<ffffffff81244f73>] deactivate_locked_super+0x43/0x70

[2493420.409945]  [<ffffffff8124547a>] deactivate_super+0x5a/0x60

[2493420.415770]  [<ffffffff81264b2f>] cleanup_mnt+0x3f/0x90

[2493420.421169]  [<ffffffff81264bc2>] __cleanup_mnt+0x12/0x20

[2493420.426733]  [<ffffffff810a7b50>] task_work_run+0x80/0xa0

[2493420.432306]  [<ffffffff810032ba>] exit_to_usermode_loop+0xaa/0xb0

[2493420.438572]  [<ffffffff81003baa>] syscall_return_slowpath+0xaa/0xb0

[2493420.445011]  [<ffffffff8171a783>] entry_SYSCALL_64_fastpath+0xc3/0xc5

[2493420.451623] Code: 60 04 00 00 48 8b 80 e0 00 00 <0f> 0b 49 c7 c7 88 ff 34 a0 49 8b

[2493420.459829] RIP  [<ffffffffa031a8df>] ext4_put_super+0x36f/0x3c0 [ext4]

[2493420.466633]  RSP <ffffc90000017de8>

crash>

通过dmesg日志，我们可以通过两个方法判断 bug的代码位置：

1. [2493420.219336] kernel BUG at fs/ext4/super.c:879!

2. [2493420.273425] RIP: 0010:[<ffffffffa031a8df>]  [<ffffffffa031a8df>] ext4_put_super+0x36f/0x3c0 [ext4]

其中（0x36f代表和ext4_put_super函数入口的偏移量，0x3c0是基准地址 ）

从2找到代码crash的具体位置：

(gdb) p 0x36f

$11 = 879

反汇编函数，找到位置

crash> dis -l ext4_put_super

在crash中查看代码

crash本身是可以查看代码的，前提是你需要加载模块，比如：

加载模块ext4：

crash> mod -s ext4

crash> mod  <<----列出所有的模块

第879行：

crash> l *ext4_put_super+0x36f

0xffffffffa031a8df is in ext4_put_super (fs/ext4/super.c:879).

874              * isn't empty.  The on-disk one can be non-empty if we've

875              * detected an error and taken the fs readonly, but the

876              * in-memory list had better be clean by this point. */

877             if (!list_empty(&sbi->s_orphan))

878                     dump_orphan_list(sb, sbi);

879             J_ASSERT(list_empty(&sbi->s_orphan));

880

881             sync_blockdev(sb->s_bdev);

882             invalidate_bdev(sb->s_bdev);

883             if (sbi->journal_bdev && sbi->journal_bdev != sb->s_bdev) {

只有当我们找到具体的代码，才能进一步分析代码，究竟为什么会crash，比如，这个函数的参数（可能是某个struct）的值到底是什么？

bt打印栈

bt栈[exception RIP: ext4_put_super+879] 有可以看到是在函数ext4_put_super 的第879行

crash> bt

PID: 1      TASK: ffff887e45918000  CPU: 58  COMMAND: "systemd-shutdow"

 #0 [ffffc90000017a58] machine_kexec at ffffffff810603e8

 #1 [ffffc90000017ab8] __crash_kexec at ffffffff811211cd

 #2 [ffffc90000017b80] __crash_kexec at ffffffff811212a5

 #3 [ffffc90000017b98] crash_kexec at ffffffff811212eb

 #4 [ffffc90000017bb8] oops_end at ffffffff81030905

 #5 [ffffc90000017be0] die at ffffffff81030ddb

 #6 [ffffc90000017c10] do_trap at ffffffff8102df02

 #7 [ffffc90000017c60] do_error_trap at ffffffff8102e2d9

 #8 [ffffc90000017d20] do_invalid_op at ffffffff8102e830

 #9 [ffffc90000017d30] invalid_op at ffffffff8171b63e

    [exception RIP: ext4_put_super+879]

    RIP: ffffffffa031a8df  RSP: ffffc90000017de8  RFLAGS: 00010206

    RAX: ffff88490edabf50  RBX: ffff887e43299000  RCX: 00000001949b336d

    RDX: 0000000000000000  RSI: 0000000000000206  RDI: 0000000000000206

    RBP: ffffc90000017e18   R8: 00000000000081a4   R9: 0000000000000000

    R10: 0000000000000cb8  R11: 0000000000001e92  R12: ffff887e43299278

    R13: ffff887e43298800  R14: ffff887e43299278  R15: ffffffffa034ff88

    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018

#10 [ffffc90000017de0] ext4_put_super at ffffffffa031a91c [ext4]

#11 [ffffc90000017e20] generic_shutdown_super at ffffffff81244aaf

#12 [ffffc90000017e40] kill_block_super at ffffffff81244e37

#13 [ffffc90000017e60] deactivate_locked_super at ffffffff81244f73

#14 [ffffc90000017e80] deactivate_super at ffffffff8124547a

#15 [ffffc90000017e98] cleanup_mnt at ffffffff81264b2f

#16 [ffffc90000017eb0] __cleanup_mnt at ffffffff81264bc2

#17 [ffffc90000017ec0] task_work_run at ffffffff810a7b50

#18 [ffffc90000017f00] exit_to_usermode_loop at ffffffff810032ba

#19 [ffffc90000017f30] syscall_return_slowpath at ffffffff81003baa

#20 [ffffc90000017f50] entry_SYSCALL_64_fastpath at ffffffff8171a783

    RIP: 00007f3241195c47  RSP: 00007fffb3db5438  RFLAGS: 00000246

    RAX: 0000000000000000  RBX: 0000560b87fbd920  RCX: 00007f3241195c47

    RDX: 0000000000000000  RSI: 0000000000000000  RDI: 0000560b87fbdd10

    RBP: 0000560b87fbda00   R8: 0000000000000000   R9: 00007f32410e416d

    R10: 0000000000000021  R11: 0000000000000246  R12: 0000560b87fbdd10

    R13: 00007fffb3db5538  R14: 00007fffb3db5523  R15: 0000000000000000

    ORIG_RAX: 00000000000000a6  CS: 0033  SS: 002b

crash>

反汇编上下函数

当我们，分析到了出错的具体的代码行，下一步需要分析，传入的参数和struct

首先，我们需要看下函数 ext4_put_super的原型，发现是static void ext4_put_super(struct super_block *sb),只有一个参数，而且是一个结构体struct super_block, 现在我们需要知道 *sb 指针的地址是多少呢？那这个地址肯定是上个函数 generic_shutdown_super 传递给它的.

现在分析的关键是，我们需要知道,当generic_shutdown_super在 ffffffff81244aaf 处，调用到 ext4_put_super的时候，传给 ext4_put_super 的指针地址是多少？

首先，需要反汇编函数generic_shutdown_super 找到地址ffffffff81244aaf

crash> dis -l generic_shutdown_super

/usr/src/debug/kernel-4.9.79-009.ali3000/linux-4.9.79-009.ali3000.alios7.x86_64/fs/super.c: 436

0xffffffff81244aa0 <generic_shutdown_super+96>: mov    0x30(%r12),%rax

0xffffffff81244aa5 <generic_shutdown_super+101>:        test   %rax,%rax

0xffffffff81244aa8 <generic_shutdown_super+104>:        je     0xffffffff81244aaf <generic_shutdown_super+111>

/usr/src/debug/kernel-4.9.79-009.ali3000/linux-4.9.79-009.ali3000.alios7.x86_64/fs/super.c: 437

0xffffffff81244aaa <generic_shutdown_super+106>:        mov    %rbx,%rdi   <===rbx 和 rdi 数据一致

0xffffffff81244aad <generic_shutdown_super+109>:        callq  *%rax     <===在这里调用下个函数

/usr/src/debug/kernel-4.9.79-009.ali3000/linux-4.9.79-009.ali3000.alios7.x86_64/include/linux/compiler.h: 243

0xffffffff81244aaf <generic_shutdown_super+111>:        mov    0x608(%rbx),%rax

/usr/src/debug/kernel-4.9.79-009.ali3000/linux-4.9.79-009.ali3000.alios7.x86_64/fs/super.c: 439

0xffffffff81244ab6 <generic_shutdown_super+118>:        lea    0x608(%rbx),%rdx

0xffffffff81244abd <generic_shutdown_super+125>:        cmp    %rax,%rdx

0xffffffff81244ac0 <generic_shutdown_super+128>:        jne    0xffffffff81244b1f <generic_shutdown_super+223>

接着，反汇编ext4_put_super , 你会发现push了很多的寄存器的值到stack

crash> dis -l ext4_put_super

/usr/src/debug/kernel-4.9.79-009.ali3000/linux-4.9.79-009.ali3000.alios7.x86_64/fs/ext4/super.c: 824

0xffffffffa031a570 <ext4_put_super>:    nopl   0x0(%rax,%rax,1) [FTRACE NOP]

0xffffffffa031a575 <ext4_put_super+5>:  push   %rbp

0xffffffffa031a576 <ext4_put_super+6>:  mov    %rsp,%rbp

0xffffffffa031a579 <ext4_put_super+9>:  push   %r15   <===第1个寄存器入栈

0xffffffffa031a57b <ext4_put_super+11>: push   %r14   <===第2个寄存器入栈

0xffffffffa031a57d <ext4_put_super+13>: push   %r13   <===第3个寄存器入栈

0xffffffffa031a57f <ext4_put_super+15>: push   %r12   <===第4个寄存器入栈

0xffffffffa031a581 <ext4_put_super+17>: mov    %rdi,%r13

0xffffffffa031a584 <ext4_put_super+20>: push   %rbx   <===第5个寄存器入栈（rbx是在上个函数的时候，就有值的，所以，ext4_put_super函数的第一个参数的指针的地址就是这个寄存器的值）

0xffffffffa031a585 <ext4_put_super+21>: sub    $0x8,%rsp

0xffffffffa031a589 <ext4_put_super+25>: mov    0x460(%rdi),%rbx

/usr/src/debug/kernel-4.9.79-009.ali3000/linux-4.9.79-009.ali3000.alios7.x86_64/fs/ext4/super.c: 826

0xffffffffa031a590 <ext4_put_super+32>: mov    0xe0(%rbx),%r14

/usr/src/debug/kernel-4.9.79-009.ali3000/linux-4.9.79-009.ali3000.alios7.x86_64/fs/ext4/super.c: 830

0xffffffffa031a597 <ext4_put_super+39>: callq  0xffffffffa03133f0 <ext4_unregister_li_request>

crash> bt -f

#10 [ffffc90000017de0] ext4_put_super at ffffffffa031a91c [ext4]

    ffffc90000017de8: 9cbae75a00000000(           ) ffff887e43298800(第5个寄存器的值)

    ffffc90000017df8: ffffffffa034a5e0(第4个寄存器的值) ffff887e3818c7b8(第3个寄存器的值)

    ffffc90000017e08: 0000000000000000(第2个寄存器的值) ffff887e45918bb0(第1个寄存器的值)

    ffffc90000017e18: ffffc90000017e38 ffffffff81244aaf(这两个是不代表寄存器的)

#11 [ffffc90000017e20] generic_shutdown_super at ffffffff81244aaf

    ffffc90000017e28: 0000000000000083 ffff887e357b8680

    ffffc90000017e38: ffffc90000017e58 ffffffff81244e37

crash> struct super_block ffff887e43298800

struct super_block {

  s_list = {

    next = 0xffffffff81cb3db0 <super_blocks>,    <=======这里也验证了，就是地址ffff887e43298800表示的就是 struct super_block

    prev = 0xffff887e43968800

  },

  s_dev = 271581185,

  s_blocksize_bits = 12 '\f',

  s_blocksize = 4096,

  s_maxbytes = 17592186040320,

  s_type = 0xffffffffa03589c0 <ext4_fs_type>,

  s_op = 0xffffffffa034a5e0 <ext4_sops>,

  dq_op = 0xffffffffa034a720 <ext4_quota_operations>,

  s_qcop = 0xffffffff81843f60 <dquot_quotactl_sysfile_ops>,

  s_export_op = 0xffffffffa034a580 <ext4_export_ops>,

  s_flags = 805371904,

  s_iflags = 1,

  s_magic = 61267,

  s_root = 0x0,

  s_umount = {

    count = {

      counter = -4294967295

    },

    wait_list = {

      next = 0xffff887e43298878,

      prev = 0xffff887e43298878

    },

    wait_lock = {

      raw_lock = {

        val = {

          counter = 0

        }

      }

Refers

https://blog.csdn.net/u013982161/article/details/51347944