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From: Nikolaus Rath <>
To: Bernd Schubert <>
	Linux FS Devel <>,
	miklos <>, Wouter Verhelst <>
Subject: Re: Why do NBD requests prevent hibernation, and FUSE requests do not?
Date: Wed, 07 Sep 2022 16:50:17 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <> (Bernd Schubert's message of "Wed, 31 Aug 2022 01:02:16 +0200")

On Aug 31 2022, Bernd Schubert <> wrote:
> 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
> A bit down the thread you can find a reference to this ancient patch

Interesting, thank you for the link! So it seems that I just got lucky
with FUSE.

Does anyone know in which order the kernel freezes processes by default?
Could I perhaps work around the problem by calling the FUSE/NBD daemon
something like "zzzzz_mydaemon"?


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             »Time flies like an arrow, fruit flies like a Banana.«

  reply	other threads:[~2022-09-07 15:50 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-30  6:31 Why do NBD requests prevent hibernation, and FUSE requests do not? Nikolaus Rath
2022-08-30 23:02 ` Bernd Schubert
2022-09-07 15:50   ` Nikolaus Rath [this message]
2022-09-02 12:49 ` Wouter Verhelst
2022-09-07 10:18   ` Nikolaus Rath
2022-09-16  8:05   ` Nikolaus Rath

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