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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Wed, 11 May 2022 09:54:07 +0200
Message-ID: <CAJfpegvUZheWb3eJwVrpBDYzwQH=zQsuq9R8mpcXb3fqzzEdiQ@mail.gmail.com>
Subject: Re: [PATCH 0/2] Prevent re-use of FUSE superblock after force unmount
To:     Daniil Lunev <dlunev@chromium.org>
Cc:     linux-fsdevel@vger.kernel.org,
        fuse-devel <fuse-devel@lists.sourceforge.net>,
        linux-kernel@vger.kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>
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On Wed, 11 May 2022 at 09:36, Daniil Lunev <dlunev@chromium.org> wrote:
>
> On Wed, May 11, 2022 at 5:07 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > On Wed, 11 May 2022 at 03:31, Daniil Lunev <dlunev@chromium.org> wrote:
> > >
> > > Force unmount of fuse severes the connection between FUSE driver and its
> > > userspace counterpart.
> >
> > Why is forced umount being used in the first place?
>
> To correctly suspend-resume. We have been using this force unmount historically
> to circumvent the suspend-resume issues which periodically occur with fuse.
> We observe FUSE rejecting to remount the device because of the issue this
> patchset attempts to address after the resume if there are still open
> file handles
> holding old super blocks. I am not sure if fuse's interaction with suspend is
> something that has been resolved systematically (we are also trying to
> figure that
> out).

No progress has been made in the past decade with regard to suspend.
I mainly put that down to lack of interest.

>  Regardless of that, doing force unmount of a mount point is a legitimate
> operation, and with FUSE it may leave the system in a state that is returning
> errors for other legitimate operations.

It is a legitimate operation, but one that is not guaranteed to leave
the system in a clean state.

Thanks,
Miklos