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:[
    
     ]  [
     
      ] 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]  [
      
       ] generic_shutdown_super+0x6f/0x100[2493420.397676]  [
       
        ] kill_block_super+0x27/0x70[2493420.403508]  [
        
         ] deactivate_locked_super+0x43/0x70[2493420.409945]  [
         
          ] deactivate_super+0x5a/0x60[2493420.415770] [
          
           ] cleanup_mnt+0x3f/0x90[2493420.421169] [
           
            ] __cleanup_mnt+0x12/0x20[2493420.426733] [
            
             ] task_work_run+0x80/0xa0[2493420.432306] [
             
              ] exit_to_usermode_loop+0xaa/0xb0[2493420.438572] [
              
               ] syscall_return_slowpath+0xaa/0xb0[2493420.445011] [
               
                ] 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 [
                
                 ] ext4_put_super+0x36f/0x3c0 [ext4][2493420.466633] RSP 
                 
                  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:[
    
     ]  [
     
      ] 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 ext4crash> mod  <<----列出所有的模块

第879行：

crash> l *ext4_put_super+0x36f0xffffffffa031a8df is in ext4_put_super (fs/ext4/super.c:879).874              * isn't empty.  The on-disk one can be non-empty if we've875              * detected an error and taken the fs readonly, but the876              * 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));880881             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> btPID: 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: 002bcrash>

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: 4360xffffffff81244aa0 
    
     : mov    0x30(%r12),%rax0xffffffff81244aa5 
     
      :        test   %rax,%rax0xffffffff81244aa8 
      
       :        je     0xffffffff81244aaf 
       
        /usr/src/debug/kernel-4.9.79-009.ali3000/linux-4.9.79-009.ali3000.alios7.x86_64/fs/super.c: 4370xffffffff81244aaa 
        
         :        mov    %rbx,%rdi   <===rbx 和 rdi 数据一致0xffffffff81244aad 
         
          : 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: 2430xffffffff81244aaf 
          
           : 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: 4390xffffffff81244ab6 
           
            : lea 0x608(%rbx),%rdx0xffffffff81244abd 
            
             : cmp %rax,%rdx0xffffffff81244ac0 
             
              : jne 0xffffffff81244b1f 
              
             
            
           
          
         
        
       
      
     
    

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: 8240xffffffffa031a570 
    
     :    nopl   0x0(%rax,%rax,1) [FTRACE NOP]0xffffffffa031a575 
     
      :  push   %rbp0xffffffffa031a576 
      
       :  mov    %rsp,%rbp0xffffffffa031a579 
       
        :  push   %r15   <===第1个寄存器入栈0xffffffffa031a57b 
        
         : push   %r14   <===第2个寄存器入栈0xffffffffa031a57d 
         
          : push %r13 <===第3个寄存器入栈0xffffffffa031a57f 
          
           : push %r12 <===第4个寄存器入栈0xffffffffa031a581 
           
            : mov %rdi,%r130xffffffffa031a584 
            
             : 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 
             
              : sub $0x8,%rsp0xffffffffa031a589 
              
               : 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: 8260xffffffffa031a590 
               
                : 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: 8300xffffffffa031a597 
                
                 : callq 0xffffffffa03133f0 
                 
                
               
              
             
            
           
          
         
        
       
      
     
    

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 ffff887e43298800struct super_block {  s_list = {    next = 0xffffffff81cb3db0 
    
     ,    <=======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 
     
      ,  s_op = 0xffffffffa034a5e0 
      
       ,  dq_op = 0xffffffffa034a720 
       
        ,  s_qcop = 0xffffffff81843f60 
        
         ,  s_export_op = 0xffffffffa034a580 
         
          , 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