Re: [PATCH 5/8] fuse: don't use ->d_time

[Al Viro]

On Wed, Jun 22, 2016 at 04:35:07PM +0200, Miklos Szeredi wrote:
> Store in memory pointed to by ->d_fsdata.  Use ->d_allocate() to allocate
> the storage.
> 
> We could cast ->d_fsdata directly on 64bit archs, but I don't think this is
> worth the extra complexity.

Now, _that_ is interesting:

> +static void fuse_dentry_release(struct dentry *dentry)
> +{
> +	kfree(dentry->d_fsdata);
> +}

What happens to fuse_dentry_revalidate() called on dentry in process of
getting dropped?  Unlike freeing struct dentry itself, ->d_release() is
not RCU-delayed.  So you are risking dereference of ->d_fsdata after
kfree(); at the very least, it needs RCU-delayed freeing...