Re: [PATCH] [RFC] vfs: don't revalidate dentries that serve as mountpoints

[Shirish Pargaonkar <shirishpargaonkar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

For a similar issue in cifs vfs (samba bugzilla 8950), I was going to try
unset the bit DCACHE_OP_REVALIDATE of d_flags of the
dentry.  Would something like work for the mountpoint dentry?



On Mon, Nov 4, 2013 at 7:16 PM, Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> We had a couple of reports of people that are mounting NFS filesystems,
> and then bind mounting certain local files onto dentries in that nfs
> mount (sort of like a poor-man's unionmount).
>
> This all works well until the dentry serving as the mountpoint fails
> d_revalidate. The dentry will end up being invalidated which makes the
> bind mount unreachable via pathwalk.
>
> It doesn't make much sense to me to allow dentries to serve as
> mountpoints to end up invalidated, so there's no real point in
> attempting to d_revalidate them at all.
>
> Reported-by: Patrick McLean <chutzpah-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org>
> Reported-by: Guang Cheng Li <liguangc-vtt25B2cwJLQT0dZR+AlfA@public.gmane.org>
> Signed-off-by: Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
>  fs/namei.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index caa2805..5b10ad0 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -585,6 +585,9 @@ drop_root_mnt:
>
>  static inline int d_revalidate(struct dentry *dentry, unsigned int flags)
>  {
> +       /* dentries that serve as mountpoints are always considered valid */
> +       if (d_mountpoint(dentry))
> +               return 1;
>         return dentry->d_op->d_revalidate(dentry, flags);
>  }
>
> --
> 1.8.3.1
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html