Re: WARN_ON(fuse_insert_writeback(root, wpa)) in tree_insert()

[Qian Cai]

On Thu, 2020-10-29 at 16:20 +0100, Miklos Szeredi wrote:
> On Thu, Oct 29, 2020 at 4:02 PM Qian Cai <cai@xxxxxxxxxx> 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.