linux-kernel - Re: [PATCH 2/2] of: __of_detach_node()

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Date:   Fri, 14 Dec 2018 11:20:01 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     mwb@...ux.vnet.ibm.com,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        tlfalcon@...ux.vnet.ibm.com, minkim@...ibm.com,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] of: __of_detach_node() - remove node from phandle cache

On Fri, Dec 14, 2018 at 12:43 AM <frowand.list@...il.com> wrote:
>
> From: Frank Rowand <frank.rowand@...y.com>
>
> Non-overlay dynamic devicetree node removal may leave the node in
> the phandle cache.  Subsequent calls to of_find_node_by_phandle()
> will incorrectly find the stale entry.  Remove the node from the
> cache.
>
> Add paranoia checks in of_find_node_by_phandle() as a second level
> of defense (do not return cached node if detached, do not add node
> to cache if detached).
>
> Reported-by: Michael Bringmann <mwb@...ux.vnet.ibm.com>
> Signed-off-by: Frank Rowand <frank.rowand@...y.com>
> ---
>  drivers/of/base.c       | 29 ++++++++++++++++++++++++++++-
>  drivers/of/dynamic.c    |  3 +++
>  drivers/of/of_private.h |  4 ++++
>  3 files changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index d599367cb92a..34a5125713c8 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -162,6 +162,27 @@ int of_free_phandle_cache(void)
>  late_initcall_sync(of_free_phandle_cache);
>  #endif
>
> +/*
> + * Caller must hold devtree_lock.
> + */
> +void __of_free_phandle_cache_entry(phandle handle)
> +{
> +       phandle masked_handle;
> +
> +       if (!handle)
> +               return;
> +
> +       masked_handle = handle & phandle_cache_mask;
> +
> +       if (phandle_cache) {
> +               if (phandle_cache[masked_handle] &&
> +                   handle == phandle_cache[masked_handle]->phandle) {
> +                       of_node_put(phandle_cache[masked_handle]);
> +                       phandle_cache[masked_handle] = NULL;
> +               }
> +       }
> +}
> +
>  void of_populate_phandle_cache(void)
>  {
>         unsigned long flags;
> @@ -1209,11 +1230,17 @@ struct device_node *of_find_node_by_phandle(phandle handle)
>                 if (phandle_cache[masked_handle] &&
>                     handle == phandle_cache[masked_handle]->phandle)
>                         np = phandle_cache[masked_handle];
> +               if (np && of_node_check_flag(np, OF_DETACHED)) {
> +                       of_node_put(np);
> +                       phandle_cache[masked_handle] = NULL;

This should never happen, right? Any time we set OF_DETACHED, the
entry should get removed from the cache. I think we want a WARN here
in case we're in an unexpected state.

Rob