Re: [PATCH] fuse: In fuse_flush only wait if someone wants the return code

Tycho Andersen
2022-09-26T15:32:13Z

Hi,

On Mon, Sep 19, 2022 at 09:03:47AM -0600, Tycho Andersen wrote:
> Hi Miklos,
>
> On Thu, Sep 01, 2022 at 08:06:47AM -0600, Tycho Andersen wrote:
> > From: "Eric W. Biederman" <ebiederm@xmission.com>
> >
> > In my very light testing this resolves a hang where a thread of the
> > fuse server was accessing the fuse filesystem (the fuse server is
> > serving up), when the fuse server is killed.
> >
> > The practical problem is that the fuse server file descriptor was
> > being closed after the file descriptor into the fuse filesystem so
> > that the fuse filesystem operations were being blocked for instead of
> > being aborted. Simply skipping the unnecessary wait resolves this
> > issue.
> >
> > This is just a proof of concept and someone should look to see if the
> > fuse max_background limit could cause a problem with this approach.
> >
> > Additionally testing PF_EXITING is a very crude way to tell if someone
> > wants the return code from the vfs flush operation. As such in the
> > long run it probably makes sense to get some direct vfs support for
> > knowing if flush needs to block until all of the flushing is complete
> > and a status/return code can be returned.
> >
> > Unless I have missed something this is a generic optimization that can
> > apply to many network filesystems.
> >
> > Al, vfs folks? (igrab/iput sorted so as not to be distractions).
> >
> > Perhaps a .flush_async method without a return code and a
> > filp_close_async function without a return code to take advantage of
> > this in the general sense.
> >
> > Waiting potentially indefinitely for user space in do_exit seems like a
> > bad idea. Especially when all that the wait is for is to get a return
> > code that will never be examined.
> >
> > Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> > [tycho: small fixups for releasing fuse file + nocred flag]
> > Signed-off-by: Tycho Andersen <tycho@tycho.pizza>
> > Reported-by: Tycho Andersen <tycho@tycho.pizza>
> > Tested-by: "Serge E. Hallyn" <serge@hallyn.com>
>
> Any chance you're willing to take this patch? We're still seeing this
> a lot and it would be great to get it fixed.

Another ping here, can someone take this? Miklos?

Thanks,

Tycho