Why dump_stack results different so much?

[Xin Zhao <uszhaoxin@gmail.com>]

I tried to use dump_stack to dump the calling trace in the kernel.
What I did is  adding a dump_stack() call in the sys_open function.

Below is the dump out result:
Jul 28 17:33:31 normal kernel:  [<c0151601>] sys_open+0xa6/0xb7
Jul 28 17:33:31 normal kernel:  [<c0108e2c>] syscall_call+0x7/0xb

However, if I insert a new kernel module which does nothing but
pointing the orignal sys_open to our_sys_open(), and in
our_system_open(), I simply do return sys_open();

I supprisely noticed that the dump_stack results are quite different!
Why did I get the calling traces below our_ssy_open() and above
syscall_call()?  Any thought on this? Many thanks!

Jul 28 17:33:42 normal kernel:  [<c0151601>] sys_open+0xa6/0xb7
Jul 28 17:33:42 normal kernel:  [<d080f02c>] our_sys_open+0x2c/0x33 [trace]
Jul 28 17:33:42 normal kernel:  [<c0114984>] __wake_up+0x41/0x81
Jul 28 17:33:42 normal kernel:  [<c02c5e44>] sbf_read+0x5a/0x6f
Jul 28 17:33:42 normal kernel:  [<c01c4e12>] journal_stop+0x159/0x279
Jul 28 17:33:42 normal kernel:  [<c01b7aff>] ext3_mark_iloc_dirty+0x25/0x2f
Jul 28 17:33:42 normal kernel:  [<c02c5e44>] sbf_read+0x5a/0x6f
Jul 28 17:33:42 normal kernel:  [<c01b7bef>] ext3_mark_inode_dirty+0x3d/0x44
Jul 28 17:33:42 normal kernel:  [<c02c5e44>] sbf_read+0x5a/0x6f
Jul 28 17:33:42 normal kernel:  [<c01c583a>] __journal_file_buffer+0xbb/0x282
Jul 28 17:33:42 normal kernel:  [<c01546ed>] bh_lru_install+0xc3/0xdf
Jul 28 17:33:42 normal kernel:  [<c01c4169>] do_get_write_access+0x36f/0x5ea
Jul 28 17:33:42 normal kernel:  [<c01c583a>] __journal_file_buffer+0xbb/0x282
Jul 28 17:33:42 normal kernel:  [<c01c4a39>] journal_dirty_metadata+0xf4/0x16d
Jul 28 17:33:42 normal kernel:  [<c0114984>] __wake_up+0x41/0x81
Jul 28 17:33:42 normal kernel:  [<c01c4e12>] journal_stop+0x159/0x279
Jul 28 17:33:42 normal kernel:  [<c01b7aff>] ext3_mark_iloc_dirty+0x25/0x2f
Jul 28 17:33:42 normal kernel:  [<c01b7bef>] ext3_mark_inode_dirty+0x3d/0x44
Jul 28 17:33:42 normal kernel:  [<c01bc111>] __ext3_journal_stop+0x1e/0x44
Jul 28 17:33:42 normal kernel:  [<c01b7c5c>] ext3_dirty_inode+0x66/0x7b
Jul 28 17:33:42 normal kernel:  [<c01736fc>] __mark_inode_dirty+0xec/0x1ce
Jul 28 17:33:42 normal kernel:  [<c011cbd4>] current_fs_time+0x4d/0x5b
Jul 28 17:33:42 normal kernel:  [<c0107606>] __switch_to+0x2a/0x365
Jul 28 17:33:42 normal kernel:  [<c0107606>] __switch_to+0x2a/0x365
Jul 28 17:33:42 normal kernel:  [<c0132c3d>] find_get_page+0x30/0x6a
Jul 28 17:33:42 normal kernel:  [<c015f35b>] do_lookup+0x24/0x89
Jul 28 17:33:42 normal kernel:  [<c01686fc>] dput+0x95/0x252
Jul 28 17:33:42 normal kernel:  [<c015ff9d>] link_path_walk+0xbdd/0xe86
Jul 28 17:33:42 normal kernel:  [<c0121778>] free_uid+0x1c/0x6d
Jul 28 17:33:42 normal kernel:  [<c01e63de>] copy_to_user+0x3c/0x4a
Jul 28 17:33:42 normal kernel:  [<c015b519>] cp_new_stat64+0xf5/0x105
Jul 28 17:33:42 normal kernel:  [<c015b55a>] sys_stat64+0x31/0x36
Jul 28 17:33:42 normal kernel:  [<c0108e2c>] syscall_call+0x7/0xb
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