linux-kernel - Re: [PATCH 5/6] fuse: fix synchronous case of fuse_file

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Message-ID: <CAJfpegsWoaqR1vQRq8QpYdwUX9Ace9XTe77eOkOUy2VyHUeEdQ@mail.gmail.com>
Date:	Fri, 22 Aug 2014 16:08:19 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Maxim Patlasov <MPatlasov@...allels.com>
Cc:	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	Anand Avati <avati@...ster.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] fuse: fix synchronous case of fuse_file_put()

On Thu, Aug 21, 2014 at 6:09 PM, Maxim Patlasov <MPatlasov@...allels.com> wrote:
> If fuse_file_put() is called with sync==true, the user may be blocked for
> a while, until userspace ACKs our FUSE_RELEASE request. This blocking must be
> uninterruptible. Otherwise request could be interrupted, but file association
> in user space remains.
>
> Signed-off-by: Maxim Patlasov <mpatlasov@...allels.com>
> ---
>  fs/fuse/file.c |    4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index cd55488..b92143a 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -136,6 +136,10 @@ static void fuse_file_put(struct fuse_file *ff, bool sync)
>                         path_put(&req->misc.release.path);
>                         fuse_put_request(ff->fc, req);
>                 } else if (sync) {
> +                       /* Must force. Otherwise request could be interrupted,
> +                        * but file association in user space remains.
> +                        */
> +                       req->force = 1;
>                         req->background = 0;
>                         fuse_request_send(ff->fc, req);
>                         path_put(&req->misc.release.path);
>


Some thought needs to go into this:  if RELEASE is interrupted, then
we should possibly allow that, effectively backgrounding the request.

The synchronous nature is just an optimization and we really don't
know where we are being interrupted, possibly in a place which very
much *should* allow interruption.

Also fuse really should distinguish fatal and non-fatal interruptions
and handle them accordingly...

Thanks,
Miklos
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