On 10/04/17 08:19, Rob Herring wrote:
> On Mon, Oct 2, 2017 at 10:53 PM, <frowand.list@xxxxxxxxx> wrote:
>> From: Frank Rowand <frank.rowand@xxxxxxxx>
>>
>> The process of applying an overlay consists of:
>> - unflatten an overlay FDT (flattened device tree) into an
>> EDT (expanded device tree)
>> - fixup the phandle values in the overlay EDT to fit in a
>> range above the phandle values in the live device tree
>> - create the overlay changeset to reflect the contents of
>> the overlay EDT
>> - apply the overlay changeset, to modify the live device tree,
>> potentially changing the maximum phandle value in the live
>> device tree
>>
>> There is currently no protection against two overlay applies
>> concurrently determining what range of phandle values are in use
>> in the live device tree, and subsequently changing that range.
>> Add a mutex to prevent multiple overlay applies from occurring
>> simultaneously.
>>
>> Ignoring 2 checkpatch warnings: Prefer using '"%s...", __func__'
>> so that the WARN() string will be more easily grepped.
>>
>> Signed-off-by: Frank Rowand <frank.rowand@xxxxxxxx>
>> ---
>> drivers/gpu/drm/tilcdc/tilcdc_slave_compat.c | 7 +++++++
>> drivers/of/overlay.c | 22 ++++++++++++++++++++++
>> drivers/of/unittest.c | 21 +++++++++++++++++++++
>> include/linux/of.h | 19 +++++++++++++++++++
>> 4 files changed, 69 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/tilcdc/tilcdc_slave_compat.c b/drivers/gpu/drm/tilcdc/tilcdc_slave_compat.c
>> index 7a7be0515bfd..c99f7924b1c6 100644
>> --- a/drivers/gpu/drm/tilcdc/tilcdc_slave_compat.c
>> +++ b/drivers/gpu/drm/tilcdc/tilcdc_slave_compat.c
>> @@ -221,6 +221,11 @@ static void __init tilcdc_convert_slave_node(void)
>> goto out;
>> }
>>
>> + /*
>> + * protect from of_resolve_phandles() through of_overlay_apply()
>> + */
>> + of_overlay_mutex_lock();
>> +
>
> We can't be relying on callers to get the locking right...
Agreed.
>
>> overlay = tilcdc_get_overlay(&kft);
>> if (!overlay)
>> goto out;
>> @@ -256,6 +261,8 @@ static void __init tilcdc_convert_slave_node(void)
>> pr_info("%s: ti,tilcdc,slave node successfully converted\n",
>> __func__);
>> out:
>> + of_overlay_mutex_unlock();
>> +
>> kfree_table_free(&kft);
>> of_node_put(i2c);
>> of_node_put(slave);
>> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
>> index a0d3222febdc..4ed372af6ce7 100644
>> --- a/drivers/of/overlay.c
>> +++ b/drivers/of/overlay.c
>> @@ -71,6 +71,28 @@ static int build_changeset_next_level(struct overlay_changeset *ovcs,
>> const struct device_node *overlay_node,
>> bool is_symbols_node);
>>
>> +/*
>> + * of_resolve_phandles() finds the largest phandle in the live tree.
>> + * of_overlay_apply() may add a larger phandle to the live tree.
>> + * Do not allow race between two overlays being applied simultaneously:
>> + * mutex_lock(&of_overlay_phandle_mutex)
>> + * of_resolve_phandles()
>> + * of_overlay_apply()
>> + * mutex_unlock(&of_overlay_phandle_mutex)
>
> Why do these need to be separate functions? I think I mentioned it
> before, but essentially overlay_data_add() should be part of the
> overlay API. We may need to allow for callers to do each step, but
> generally I think the interface should just be "apply this fdt blob".
Yes, that is where I want to end up.
>
> Rob
>
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