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

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Date:   Mon, 02 Nov 2020 09:25:57 -0500
From:   Qian Cai <cai@...hat.com>
To:     Miklos Szeredi <miklos@...redi.hu>
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 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.