On 8/30/22 08:31, Nikolaus Rath wrote:
Hello,
I am comparing the behavior of FUSE and NBD when attempting to hibernate
the system.
FUSE seems to be mostly compatible, I am able to suspend the system even
when there is ongoing I/O on the fuse filesystem.
....
As far as I can tell, the problem is that while an NBD request is
pending, the atsk that waits for the result (in this case *rsync*) is
refusing to freeze. This happens even when setting a 5 minute timeout
for freezing (which is more than enough time for the NBD request to
complete), so I suspect that the NBD server task (in this case nbdkit)
has already been frozen and is thus unable to make progress.
However, I do not understand why the same is not happening for FUSE
(with FUSE requests being stuck because the FUSE daemon is already
frozen). Was I just very lucky in my tests? Or are tasks waiting for
FUSE request in a different kind of state? Or is NBD a red-herring here,
and the real trouble is with ZFS?
It would be great if someone could shed some light on what's going on.
I guess it is a generic issue also affecting fuse, see this patch
https://lore.kernel.org/lkml/20220511013057.245827-1-dlunev@xxxxxxxxxxxx/
A bit down the thread you can find a reference to this ancient patch
https://linux-kernel.vger.kernel.narkive.com/UeBWfN1V/patch-fuse-make-fuse-daemon-frozen-along-with-kernel-threads
I had also asked about NFS when the server side is down, (and so a
request reply will not come) but didn't get an answer.
- Bernd
