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

    Thanks.

    Tycho

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