crash使用总结

根据栈，确定相关函数在源码中的具体位置

想要知道该down_read所处的位置

crash> bt 1620
PID: 1620   TASK: ffff88812edb4a00  CPU: 6   COMMAND: "mount_clear_soc"
 #0 [ffffc900005e3c88] __schedule at ffffffff82248906
 #1 [ffffc900005e3d18] schedule at ffffffff82249262
 #2 [ffffc900005e3d28] rwsem_down_read_slowpath at ffffffff8224e094
 #3 [ffffc900005e3dd0] down_read at ffffffff8224e676     #想要知道该down_read所处的位置
 #4 [ffffc900005e3de0] __get_super at ffffffff8145f7a3   #执行dis -l ffffffff8145f7a3
 #5 [ffffc900005e3e18] get_super at ffffffff8145f814
 #6 [ffffc900005e3e20] __invalidate_device at ffffffff814ca4ec
 #7 [ffffc900005e3e40] nbd_ioctl at ffffffff81cd1725
 #8 [ffffc900005e3ea8] blkdev_ioctl at ffffffff81a65cbf
 #9 [ffffc900005e3ef0] block_ioctl at ffffffff814ca42a
#10 [ffffc900005e3ef8] ksys_ioctl at ffffffff8147dcb0
#11 [ffffc900005e3f30] __x64_sys_ioctl at ffffffff8147dd6e
#12 [ffffc900005e3f38] do_syscall_64 at ffffffff81003f1b
#13 [ffffc900005e3f50] entry_SYSCALL_64_after_hwframe at ffffffff82400078
    RIP: 00007f568032c577  RSP: 00007ffc7b1d6d58  RFLAGS: 00000202
    RAX: ffffffffffffffda  RBX: 0000000000000000  RCX: 00007f568032c577
    RDX: 0000000000000000  RSI: 000000000000ab04  RDI: 0000000000000003
    RBP: 0000000000001388   R8: 00007f568080c440   R9: 0000000000000000
    R10: 0000000000000003  R11: 0000000000000202  R12: 0000000000000003
    R13: 00007ffc7b1d747b  R14: 0000000000000653  R15: 0000000000000000
    ORIG_RAX: 0000000000000010  CS: 0033  SS: 002b

crash> dis -l ffffffff8145f7a3
/home/sunke/git/linux/fs/super.c: 759
0xffffffff8145f7a3 <__get_super+339>:   addq   $0x1,0x4fc9315(%rip)        # 0xffffffff86428ac0 <__gcov0.__get_super+64>

根据结构体地址，推断结构体成员的地址

已知super_block的地址为ffff88812ef99800

求成员struct rw_semaphore s_umount的地址，并分析其内容

crash> whatis -o super_block
struct super_block {
     [0] struct list_head s_list;
    [16] dev_t s_dev;
    [20] unsigned char s_blocksize_bits;
    [24] unsigned long s_blocksize;
    [32] loff_t s_maxbytes;
    [40] struct file_system_type *s_type;
    [48] const struct super_operations *s_op;
    [56] const struct dquot_operations *dq_op;
    [64] const struct quotactl_ops *s_qcop;
    [72] const struct export_operations *s_export_op;
    [80] unsigned long s_flags;
    [88] unsigned long s_iflags;
    [96] unsigned long s_magic;
   [104] struct dentry *s_root;
   [112] struct rw_semaphore s_umount;                #相对偏移为112，也就是0x70
   [152] int s_count;
   [156] atomic_t s_active;
   [160] const struct xattr_handler **s_xattr;
    ...

推测出s_umount的地址为ffff88812ef99870

然后可以看其内容了

crash> rw_semaphore ffff88812ef99870
struct rw_semaphore {
  count = {
    counter = 3
  }, 
  owner = {
    counter = -131386559987712
  }, 
  osq = {
    tail = {
      counter = 0
    }
  }, 
  wait_lock = {
    raw_lock = {
      {
        val = {
          counter = 0
        }, 
        {
          locked = 0 '\000', 
          pending = 0 '\000'
        }, 
        {
          locked_pending = 0, 
          tail = 0
        }
      }
    }
  }, 
  wait_list = {
    next = 0xffffc9000650bd60, 
    prev = 0xffffc9000650bd60
  }
}