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Subject: Re: [RFC PATCH v3 3/9] software_node: Fix failure to hold refcount in
 software_node_get_next_child
To:     Sakari Ailus <sakari.ailus@iki.fi>
Cc:     linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        linux.walleij@linaro.org, prabhakar.mahadev-lad.rj@bp.renesas.com,
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        robh@kernel.org, davem@davemloft.net, linux@rasmusvillemoes.dk,
        andriy.shevchenko@linux.intel.com, sergey.senozhatsky@gmail.com,
        rostedt@goodmis.org, pmladek@suse.com, mchehab@kernel.org,
        tian.shu.qiu@intel.com, bingbu.cao@intel.com,
        sakari.ailus@linux.intel.com, yong.zhi@intel.com,
        rafael@kernel.org, gregkh@linuxfoundation.org, kitakar@gmail.com,
        dan.carpenter@oracle.org
References: <20201019225903.14276-1-djrscally@gmail.com>
 <20201019225903.14276-4-djrscally@gmail.com>
 <20201020133148.GB843@valkosipuli.retiisi.org.uk>
From:   Dan Scally <djrscally@gmail.com>
Message-ID: <c1a7beba-faff-e06d-1517-5b30d777b252@gmail.com>
Date:   Wed, 21 Oct 2020 00:25:28 +0100
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Hi Sakari

On 20/10/2020 14:31, Sakari Ailus wrote:
> Hi Daniel,
>
> On Mon, Oct 19, 2020 at 11:58:57PM +0100, Daniel Scally wrote:
>> The software_node_get_next_child() function currently does not hold a kref
>> to the child software_node; fix that.
>>
>> Fixes: 59abd83672f7 ("drivers: base: Introducing software nodes to the firmware node framework")
>> Signed-off-by: Daniel Scally <djrscally@gmail.com>
>> ---
>> Changes in v3:
>> 	- split out from the full software_node_graph*() patch
>>
>>  drivers/base/swnode.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
>> index f01b1cc61..741149b90 100644
>> --- a/drivers/base/swnode.c
>> +++ b/drivers/base/swnode.c
>> @@ -450,7 +450,7 @@ software_node_get_next_child(const struct fwnode_handle *fwnode,
>>  		c = list_next_entry(c, entry);
>>  	else
>>  		c = list_first_entry(&p->children, struct swnode, entry);
>> -	return &c->fwnode;
>> +	return software_node_get(&c->fwnode);
> I believe similarly, the function should drop the reference to the previous
> node, and not expect the caller to do this. The OF equivalent does the
> same.

I think I prefer it this way myself, since the alternative is having to
explicitly call *_node_get() on a returned child if you want to keep it
but also keep iterating. But I agree that it's important to take a
consistent approach. I'll add that too; this will mean
swnode_graph_find_next_port() and
software_node_graph_get_next_endpoint() in patch 4 of this series will
need changing slightly to square away their references.