I have a small local network which has a Gentoo box and a Windows box. I mount a share originating on the Windows box onto the Gentoo box with a command like:

mount -t cifs -o username=WindowsUsername,password=thepassword,uid=pistos //192.168.0.103/Users /mnt/windowsbox

Most of the time, everything Just Works, and I can read and write without problems. However, every few weeks or so, the connection or the mount point seems to go dead or hang, such that any process that tries to access the mount point gets stuck in D state (disk, or I/O wait). These processes become impervious to TERM and KILL signals. Disconnecting and reconnecting the Windows box from the network does not help. The frozen state lasts for 5+ minutes. It's really frustrating and gets in the way of normal work, because it freezes Save As dialogues, ls commands, etc. If I issue a umount on the mount point, it either hangs also, or reports that the mount point is in use. Eventually, the dead state resolves itself, and the mount point gets unmounted, or it becomes possible to umount with no delay.

My guess is that this happens when the connection/mount has gone idle, or when the Windows machine has been idle. I am not really sure.

Why is this happening, and what can I do to prevent it? Or how can I successfully kill these D-state processes at will?

Possibly related: CIFS mounts hang on read