linux-kernel - Re: [PATCH v4 2/2] FUSE: Retire superblock on force unmount

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Date:   Mon, 18 Jul 2022 11:56:17 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Daniil Lunev <dlunev@...omium.org>
Cc:     linux-fsdevel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        "Theodore Ts'o" <tytso@....edu>, linux-kernel@...r.kernel.org,
        fuse-devel <fuse-devel@...ts.sourceforge.net>,
        Daniil Lunev <dlunev@...gle.com>
Subject: Re: [PATCH v4 2/2] FUSE: Retire superblock on force unmount

On Wed, 1 Jun 2022 at 03:11, Daniil Lunev <dlunev@...omium.org> wrote:
>
> From: Daniil Lunev <dlunev@...omium.org>
>
> Force unmount of FUSE severes the connection with the user space, even
> if there are still open files. Subsequent remount tries to re-use the
> superblock held by the open files, which is meaningless in the FUSE case
> after disconnect - reused super block doesn't have userspace counterpart
> attached to it and is incapable of doing any IO.
>
> Signed-off-by: Daniil Lunev <dlunev@...omium.org>
>
> Signed-off-by: Daniil Lunev <dlunev@...gle.com>

Why the double sign-off?

> ---
>
> (no changes since v3)
>
> Changes in v3:
> - No changes
>
> Changes in v2:
> - Use an exported function instead of directly modifying superblock
>
>  fs/fuse/inode.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 8c0665c5dff88..8875361544b2a 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -476,8 +476,11 @@ static void fuse_umount_begin(struct super_block *sb)
>  {
>         struct fuse_conn *fc = get_fuse_conn_super(sb);
>
> -       if (!fc->no_force_umount)
> -               fuse_abort_conn(fc);
> +       if (fc->no_force_umount)
> +               return;
> +
> +       fuse_abort_conn(fc);
> +       retire_super(sb);

And this is called for both block and non-block supers.  Which means
that the bdi will be unregistered, yet the sb could still be reused
(see fuse_test_super()).

Thanks,
Miklos