Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:6 as permitted sender) client-ip=2620:137:e000::3:6;
Message-ID: <4b641f48-7673-9d55-0963-35b52189b6ad@axentia.se>
Date:   Thu, 19 Oct 2023 11:26:41 +0200
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101
 Thunderbird/102.6.0
Subject: Re: [PATCH 3/3] i2c: muxes: i2c-mux-gpmux: Use
 of_get_i2c_adapter_by_node()
Content-Language: sv-SE
To:     Herve Codina <herve.codina@bootlin.com>,
        Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc:     linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        Allan Nielsen <allan.nielsen@microchip.com>,
        Horatiu Vultur <horatiu.vultur@microchip.com>,
        Steen Hegelund <steen.hegelund@microchip.com>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>
References: <20231019073533.386563-1-herve.codina@bootlin.com>
 <20231019073533.386563-4-herve.codina@bootlin.com>
From:   Peter Rosin <peda@axentia.se>
In-Reply-To: <20231019073533.386563-4-herve.codina@bootlin.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?L0RSRnBOZkZXcFJyUkZkdy94bHVuRHRpdHN2L1g1M3VjUDFuYk9oa0J4dE1V?=
 =?utf-8?B?NGErZVRGSlcwbURZOXlHblUyOEZaMXlGQk41KzdYZ2dHZmJ2bXpUalFDdHNF?=
 =?utf-8?B?SWRrbEUrcUtGcGtFQkVOQks3YjVzQ2NrUTZYOGVtelBvSUo3QnB4QWNFVVR5?=
 =?utf-8?B?L2Erck5mK29LdzVsNUxNeDhwTDRhYmk2ak4rWGRXQXQrUUdIeEU1MzVsWlBj?=
 =?utf-8?B?MEdINzlCM1ZMSWd0STNqSFVFRHlwZXJLUlUxbjF5bWUzL2VvSHFrQ0lVS0pJ?=
 =?utf-8?B?cW9mcFBaanVrMUJYR04zSmd3VkE4WThXOUpySExmWUxzVjNJNW9TemFKSStk?=
 =?utf-8?B?V0l1TWpWRWJkSlgwd2JucEZyMDNFN1JmZGdodXZQSi9xN0NVS3dxQXhjVzZr?=
 =?utf-8?B?cmxpTmRrOHJzM0szZGFLRDN4eDhkQjkrVURtOG5xVXAycUN0ejdCZ1NteVhm?=
 =?utf-8?B?YVVYTWdBUXRSblQvNUVaNTlaYkF3YkdtZjc2T3VSS0JvaUdLTHhtNjBtSXlo?=
 =?utf-8?B?Z0lxMy95T09xQmJTaWRXTDdRVjc2NVBvZGhBa2hIcVRJUkNoa2llNTRha2pN?=
 =?utf-8?B?MmVvSWNIemtMNWJrKytqa0d1RytFT2NycXBGcVdWZVBuUFh3T3RUMHNHaFlP?=
 =?utf-8?B?SUMrcDh6UEYzbkFFZllFamRISy95NE1HVzVFSThwODJQUXl1VjAzL0RDczlE?=
 =?utf-8?B?ZjVkWFk1cFI2NlcwTGJWczdVSnV0WE0xRWhHeWxaQVAxK05oVVhzWis5cUIz?=
 =?utf-8?B?ekgwSjdncnJ1bFFib21LTUtQazIrZHppZ3Nlcko3YzduZEs2VnUzbVlPNlpU?=
 =?utf-8?B?c1FRbEJXT3k5MWJmclZiR0N1RnY0Kzc5VlpjRjd1WnIydTgwNURsQVdhY1p3?=
 =?utf-8?B?ekl5Z2phYk9GZ3lBKzRwN0o0a2QvRWFPQmZlVWk1eFQ2MXpQWjBMclE1bFdK?=
 =?utf-8?B?eFhEbGVCRmZtNGtOekxaWkgzazM4R1VkLytYc0NURGtsOEhRTmlGdUpDR2tO?=
 =?utf-8?B?QXNLNGN0Ry8yNHBYZ055TFYyQmJkSHQzUmVrcHRkRUsrcXNxc09TRk1Bcnc0?=
 =?utf-8?B?MVNxMUF5WTByTUNNaTFVeTNXNWNLOWJCcGUyRThJeHZTWXhOelZINGJmeHlk?=
 =?utf-8?B?Ny9uUlZ0b2E5bzN2RVgyb2g3ODd5YzdLMDExcG94MTgyN2E2RlMyeUlYOWo0?=
 =?utf-8?B?TE4xTUEvVWVsQk1NZlM0Y3dLQUhTZXYrRWw0VXQ5UGtEYkMrZVVxc3hMOTBQ?=
 =?utf-8?B?anYwSG9YeEw3R3AvWmpHSEdkRDFIdG1lMlRzMmpsNS94ZlhLRFdVV2tkaEZ6?=
 =?utf-8?B?L2R3MHljNVNUVzFzMlhvZGdTU2IrUVhNZkpOdGVpdllXQkdSVTFSWWpZZHRT?=
 =?utf-8?B?WXJXcnFvR1lYNFNhSjMrSGJDRkl5ZHRFTnJvVEhDVGgrU01HMTlzNVQraVp3?=
 =?utf-8?B?YmNSU2xLT1Z0b3U2UUJ0d3Q3M01EbVc3am1VdVU2ZmpzakpwNjh4eHlkZHlN?=
 =?utf-8?B?cklTQVpZWGtRay9nWkFPUkdMNllNZTJoUi9sclgvNktyOEJEdmc4Vk1HVkhG?=
 =?utf-8?B?NlR6K0Y1Y2ZBYzcvWDk4QklTYVo3Tmt0cXZtVzZZSEJQVkRxUUNxNGRjcDdk?=
 =?utf-8?B?QStlWXBwNXpKZjdMM2hCelpKK2xzMHpyakNnOXNzMENpWFFYT3AwNXhZVE1C?=
 =?utf-8?B?SGpZK3hKdktNTjdyNHdFM1NkaURFVStCOVNPMW1DVGl1ZVJidWdTeHVNMHdE?=
 =?utf-8?B?WXdlTkd0dWxmQ0YvZmV6ZWVmT3pLRlV0ZU9pRzNzU1NIbFBhOG5uZXlDLytH?=
 =?utf-8?B?Znlsdmd3YXh1TmV3ZHlHNU1nUHFsLzVZdUZwK3pwQzVKMitMd3BXVlBpdXlq?=
 =?utf-8?B?TzlzU1pMaUhSM3IzM0dQMms3ODhxdm9senV1dVhXc2xka0NUamNBMWg4WThD?=
 =?utf-8?B?YWVBbUdjbGV1T0dSckRFc1haYk5KTkdvbXNsNm5xYU9GWEh0OSsrU3RqUEZ1?=
 =?utf-8?B?dzl1RElSbUNpQUl6RkRaWmppeWZTcjBxc04wenkzc0hBWnQ3Nlg1Uy91cExB?=
 =?utf-8?B?WnpQdlpCMStMTmYwVXliMnNyOUx4M0N3eWpzSmFKVElQZ1VrTk5uUndSMlFH?=
 =?utf-8?Q?+/zDgnsXbrs+QWc1t5e2SdUJu?=
X-OriginatorOrg: axentia.se
X-MS-Exchange-CrossTenant-Network-Message-Id: 318fe675-b526-43c3-0b78-08dbd08581af
X-MS-Exchange-CrossTenant-AuthSource: AM0PR02MB4436.eurprd02.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Oct 2023 09:26:42.9107
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4ee68585-03e1-4785-942a-df9c1871a234
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: 5pDXRLQWnwIH5dUYDWdr8XOb/BeGn1/NR+1whhJ/Ji0s/XKGktQyHzF5ogbozA5N
X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR02MB5854
X-Spam-Status: No, score=-4.2 required=5.0 tests=DKIM_SIGNED,DKIM_VALID,
	DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,
	NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS autolearn=unavailable
	autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on pete.vger.email
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (pete.vger.email [0.0.0.0]); Thu, 19 Oct 2023 02:27:07 -0700 (PDT)

Hi!

2023-10-19 at 09:35, Herve Codina wrote:
> i2c-mux-gpmux uses the pair of_find_i2c_adapter_by_node() /
> i2c_put_adapter(). These pair alone is not correct to properly lock the
> I2C parent adapter.
> 
> Indeed, i2c_put_adapter() decrements the module refcount while
> of_find_i2c_adapter_by_node() does not increment it. This leads to an
> overflow over zero of the parent adapter user counter.

Perhaps "... underflow of the parent module refcount."?

> 
> Use the dedicated function, of_get_i2c_adapter_by_node(), to handle
> correctly the module refcount.
> 
> Signed-off-by: Herve Codina <herve.codina@bootlin.com>

Good find, and sorry about that!

Fixes: ac8498f0ce53 ("i2c: i2c-mux-gpmux: new driver")
Acked-by: Peter Rosin <peda@axentia.se>

Cheers,
Peter

> ---
>  drivers/i2c/muxes/i2c-mux-gpmux.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-mux-gpmux.c b/drivers/i2c/muxes/i2c-mux-gpmux.c
> index baccf4bfaf02..8305661e1253 100644
> --- a/drivers/i2c/muxes/i2c-mux-gpmux.c
> +++ b/drivers/i2c/muxes/i2c-mux-gpmux.c
> @@ -52,7 +52,7 @@ static struct i2c_adapter *mux_parent_adapter(struct device *dev)
>  		dev_err(dev, "Cannot parse i2c-parent\n");
>  		return ERR_PTR(-ENODEV);
>  	}
> -	parent = of_find_i2c_adapter_by_node(parent_np);
> +	parent = of_get_i2c_adapter_by_node(parent_np);
>  	of_node_put(parent_np);
>  	if (!parent)
>  		return ERR_PTR(-EPROBE_DEFER);