linux-kernel - Re: [PATCH 0/2] Prevent re-use of FUSE superblock after force unmount

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Message-ID: <692c1682-ce10-7136-675b-2975f6a1aa01@fastmail.fm>
Date:   Wed, 11 May 2022 13:38:41 +0200
From:   Bernd Schubert <bernd.schubert@...tmail.fm>
To:     Daniil Lunev <dlunev@...omium.org>,
        Miklos Szeredi <miklos@...redi.hu>
Cc:     linux-fsdevel@...r.kernel.org,
        fuse-devel <fuse-devel@...ts.sourceforge.net>,
        linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 0/2] Prevent re-use of FUSE superblock after force unmount



On 5/11/22 13:19, Daniil Lunev wrote:
>> At a glance it's a gross hack.   I can think of more than one way in
>> which this could be achieved without adding a new field to struct
>> super_block.
> Can you advise what would be a better way to achieve that?
> 
>> But...  what I'd really prefer is if the underlying issue of fuse vs.
>> suspend was properly addressed instead of adding band-aids.  And that
>> takes lots more resources, for sure, and the result is not guaranteed.
>> But you could at least give it a try.
> We do have a limited success with userspace level sequencing of processes,
> but on the kernel level - it is all quite untrivial, as you mentioned.
> I did some
> research, and what I found pretty much a 9 years old thread which went
> nowhere at the end [1]. We would also prefer if suspend just worked (and
> we have a person looking into what is actually breaking with suspend), but
> there is an unbounded amount of time for how long the investigation and
> search for a solution may be ongoing given the complexity of the problem,
> and in the meantime there is no way to work around the problem.
> 
> Thanks,
> Daniil
> 
> [1] https://linux-kernel.vger.kernel.narkive.com/UeBWfN1V/patch-fuse-make-fuse-daemon-frozen-along-with-kernel-threads

So that sounds like anything that is waiting for a response cannot be 
frozen? Assuming there is an outstanding NFS request and the NFS server 
is down, suspend would not work until the NFS server comes back?

Thanks,
Bernd