linux-kernel - Re: WARN_ON(fuse_insert_writeback(root, wpa)) in tree

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Message-ID: <CAJfpegsuYAW+W7xN3QGdfzEHROdMhVOJS5K=u8JQe-_WaY8VsA@mail.gmail.com>
Date:   Fri, 6 Nov 2020 10:29:28 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Qian Cai <cai@...hat.com>
Cc:     Vivek Goyal <vgoyal@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        virtio-fs-list <virtio-fs@...hat.com>
Subject: Re: WARN_ON(fuse_insert_writeback(root, wpa)) in tree_insert()

On Mon, Nov 2, 2020 at 3:26 PM Qian Cai <cai@...hat.com> wrote:
>
> On Thu, 2020-10-29 at 16:20 +0100, Miklos Szeredi wrote:
> > On Thu, Oct 29, 2020 at 4:02 PM Qian Cai <cai@...hat.com> wrote:
> > > On Wed, 2020-10-07 at 16:08 -0400, Qian Cai wrote:
> > > > Running some fuzzing by a unprivileged user on virtiofs could trigger the
> > > > warning below. The warning was introduced not long ago by the commit
> > > > c146024ec44c ("fuse: fix warning in tree_insert() and clean up writepage
> > > > insertion").
> > > >
> > > > From the logs, the last piece of the fuzzing code is:
> > > >
> > > > fgetxattr(fd=426, name=0x7f39a69af000, value=0x7f39a8abf000, size=1)
> > >
> > > I can still reproduce it on today's linux-next. Any idea on how to debug it
> > > further?
> >
> > Can you please try the attached patch?
>
> It has survived the testing over the weekend. There is a issue that virtiofsd
> hung, but it looks like a separate issue.

Thanks very much for the testing.   Queued up the patch.

Miklos