读取sd卡上文件，一段时间会重复打印以下内容，每次开机只会出现一次；
[ 522.451312] page:c0ba0040 count:0 mapcount:0 mapping: (null) index:0x0
[ 522.457911] page flags: 0x60000200(arch_1)
[ 522.461965] [<c0185fc8>] (unwind_backtrace+0x0/0xf0) from [<c01e9c1c>] (bad_page+0xb0/0x108)
[ 522.470386] [<c01e9c1c>] (bad_page+0xb0/0x108) from [<c01eae7c>] (get_page_from_freelist+0x478/0x560)
[ 522.479586] [<c01eae7c>] (get_page_from_freelist+0x478/0x560) from [<c01eb228>] (__alloc_pages_nodemask+0xe0/0x758)
[ 522.489969] [<c01eb228>] (__alloc_pages_nodemask+0xe0/0x758) from [<c01ed48c>] (__do_page_cache_readahead+0x120/0x2ac)
[ 522.500625] [<c01ed48c>] (__do_page_cache_readahead+0x120/0x2ac) from [<c01ed8c4>] (ra_submit+0x24/0x2c)
[ 522.510075] [<c01ed8c4>] (ra_submit+0x24/0x2c) from [<c01edbc4>] (page_cache_sync_readahead+0x44/0x64)
[ 522.519349] [<c01edbc4>] (page_cache_sync_readahead+0x44/0x64) from [<c01e6158>] (generic_file_aio_read+0x474/0x834)
[ 522.529844] [<c01e6158>] (generic_file_aio_read+0x474/0x834) from [<c0214414>] (do_sync_read+0xb0/0xd4)
[ 522.539193] [<c0214414>] (do_sync_read+0xb0/0xd4) from [<c0214b94>] (vfs_read+0xb0/0x144)
[ 522.547333] [<c0214b94>] (vfs_read+0xb0/0x144) from [<c0214c68>] (sys_read+0x40/0x70)
[ 522.555141] [<c0214c68>] (sys_read+0x40/0x70) from [<c0180640>] (ret_fast_syscall+0x0/0x30)
