ZFS trim hangs during disconnect

[overflowz]

when issuing zpool trim mypool and for some reason zerofs crashes (ctrl+c or any other reason), trim command hangs forever and cannot be killed.

any thoughts or is this ZFS specific?

[Barre]

Hi,

You're experiencing a classic NBD issue where I/O operations get stuck in an uninterruptible state when the server disconnects unexpectedly.

When the NBD server crashes, any pending I/O operations (like those from zpool trim) end up waiting indefinitely in the kernel, which is why you can't kill the process. This happens because:

1. ZFS issues TRIM operations to the NBD device
2. The NBD server crashes before completing these operations
3. The kernel keeps waiting for a response that will never come

You might be able to forcibly disconnect the NBD device with:

nbd-client -d /dev/nbdX

If this is a concern, you may want to look at the "timeout" option of nbd-client https://manpages.debian.org/testing/nbd-client/nbd-client.8.en.html#t