Hi, I am writing a driver module. Now I have some questions about blocked I/O. my_read() is the read function in the file_operations struct in my module. my_read() is just as simple as this: ssize_t my_read(....) { if(wait_event_interruptible(dev->queue, a == b)) return -ERESTARTSYS; return count; } Then I write a simple program to open and read the device. Obviously the program will be blocked. Now I still can open a new shell window and log in ( I use xshell). However, then I implement my_mmap(), the mmap function in the file_operations struct in my module, like this: int my_mmap(....) { if(wait_event_interruptible(dev->queue, a == b)) return -ERESTARTSYS; return 0; } Then I write a simple program to open and mmap() the device. Obviously the program will be blocked again. However, when I open a new shell window in xshell and try to connect to the linux, it displays like this: Connecting to 192.168.146.118:22... Connection established. To escape to local shell, press 'Ctrl+Alt+]'. And I can't log in! Then after a while, in the syslog, there is one message like this: [38306.614103] INFO: task landscape-sysin:17616 blocked for more than 120 seconds. [38306.614114] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [38306.614120] landscape-sysin D ffffffff8180fb60 0 17616 17609 0x00000000 [38306.614125] ffff88031d609c90 0000000000000082 ffff88032fffdb08 0000000000000000 [38306.614130] ffff8803130bdc40 ffff88031d609fd8 ffff88031d609fd8 ffff88031d609fd8 [38306.614133] ffff88062150c530 ffff8803130bdc40 0000004100000000 ffff8803130bdc40 [38306.614137] Call Trace: [38306.614147] [<ffffffff816b2c49>] schedule+0x29/0x70 [38306.614151] [<ffffffff816b3acd>] rwsem_down_read_failed+0x9d/0xf0 [38306.614157] [<ffffffff81341824>] call_rwsem_down_read_failed+0x14/0x30 [38306.614160] [<ffffffff816b1644>] ? down_read+0x24/0x2b [38306.614166] [<ffffffff81153661>] __access_remote_vm+0x41/0x1f0 [38306.614170] [<ffffffff81153ddb>] access_process_vm+0x5b/0x80 [38306.614175] [<ffffffff811ea423>] proc_pid_cmdline+0x93/0x120 [38306.614178] [<ffffffff811eb425>] proc_info_read+0xa5/0xf0 [38306.614182] [<ffffffff81186e84>] vfs_read+0xb4/0x180 [38306.614185] [<ffffffff81187102>] SyS_read+0x52/0xa0 [38306.614189] [<ffffffff816bc8c2>] system_call_fastpath+0x16/0x1b If I terminate the program by force, then I can log in right now. So, are there any differences between the read and the mmap function to the wait_event_interruptible()? Why? If I want to block mmap() just like blocking read(), what should I do? Or it is impossible? Thanks!