Re: [PATCH 6/6] eventfs: clean up dentry ops and add revalidate function

[Al Viro]

On Tue, Jan 30, 2024 at 06:37:49PM -0800, Linus Torvalds wrote:
> On Tue, 30 Jan 2024 at 17:12, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> >
> > > + *
> > > + * Note that d_revalidate is called potentially under RCU,
> > > + * so it can't take the eventfs mutex etc. It's fine - if
> > > + * we open a file just as it's marked dead, things will
> > > + * still work just fine, and just see the old stale case.
> >
> > Looks like use after free, unless freeing ei is RCU-delayed...
> 
> We hold the ref to the ei in the very dentry that is doing d_revalidate().

What's to stop ->d_revalidate() from being called in parallel with
__dentry_kill()?