linux-kernel - Re: [PATCH v4 3/9] media: i2c: ds90ub960: Protect alias_use

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Message-ID: <73dd31df-cce6-445e-bf69-67b9854e9444@ideasonboard.com>
Date: Mon, 6 Jan 2025 11:38:43 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Romain Gantois <romain.gantois@...tlin.com>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 Kory Maincent <kory.maincent@...tlin.com>, linux-i2c@...r.kernel.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-media@...r.kernel.org, linux-gpio@...r.kernel.org,
 Wolfram Sang <wsa+renesas@...g-engineering.com>,
 Luca Ceresoli <luca.ceresoli@...tlin.com>, Andi Shyti
 <andi.shyti@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Derek Kiernan <derek.kiernan@....com>,
 Dragan Cvetic <dragan.cvetic@....com>, Arnd Bergmann <arnd@...db.de>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Linus Walleij <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>
Subject: Re: [PATCH v4 3/9] media: i2c: ds90ub960: Protect alias_use_mask with
 a mutex

Hi,

On 30/12/2024 15:22, Romain Gantois wrote:
> The aliased_addrs list represents the occupation of an RX port's hardware
> alias table. This list and the underlying hardware table are only accessed
> in the attach/detach_client() callbacks.
> 
> These functions are only called from a bus notifier handler in i2c-atr.c,
> which is always called with the notifier chain's semaphore held. This
> indirectly prevents concurrent access to the aliased_addrs list.
> However, more explicit and direct locking is preferable. Moreover, with the
> introduction of dynamic address translation in a future patch, the
> attach/detach_client() callbacks will be called from outside of the
> notifier chain's read section.
> 
> Introduce a mutex to protect access to the aliased_addrs list and its
> underlying hardware table.
> 
> Signed-off-by: Romain Gantois <romain.gantois@...tlin.com>
> ---
>   drivers/media/i2c/ds90ub960.c | 23 ++++++++++++++++++++---
>   1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/i2c/ds90ub960.c b/drivers/media/i2c/ds90ub960.c
> index 7534ddf2079fef466d3a114f0be98599427639fa..0510427ac4e9214132bcdf3fa18873ec78c48a5e 100644
> --- a/drivers/media/i2c/ds90ub960.c
> +++ b/drivers/media/i2c/ds90ub960.c
> @@ -467,6 +467,8 @@ struct ub960_rxport {
>   		};
>   	} eq;
>   
> +	/* lock for aliased_addrs and associated registers */
> +	struct mutex aliased_addrs_lock;
>   	u16 aliased_addrs[UB960_MAX_PORT_ALIASES];
>   };
>   
> @@ -1030,6 +1032,9 @@ static int ub960_atr_attach_client(struct i2c_atr *atr, u32 chan_id,
>   	struct ub960_rxport *rxport = priv->rxports[chan_id];
>   	struct device *dev = &priv->client->dev;
>   	unsigned int reg_idx;
> +	int ret = 0;
> +
> +	mutex_lock(&rxport->aliased_addrs_lock);

A mutex guard could be used here and below.

  Tomi

>   
>   	for (reg_idx = 0; reg_idx < UB960_MAX_PORT_ALIASES; reg_idx++) {
>   		if (!rxport->aliased_addrs[reg_idx])
> @@ -1038,7 +1043,8 @@ static int ub960_atr_attach_client(struct i2c_atr *atr, u32 chan_id,
>   
>   	if (reg_idx == UB960_MAX_PORT_ALIASES) {
>   		dev_err(dev, "rx%u: alias pool exhausted\n", rxport->nport);
> -		return -EADDRNOTAVAIL;
> +		ret = -EADDRNOTAVAIL;
> +		goto out_unlock;
>   	}
>   
>   	rxport->aliased_addrs[reg_idx] = client->addr;
> @@ -1051,7 +1057,9 @@ static int ub960_atr_attach_client(struct i2c_atr *atr, u32 chan_id,
>   	dev_dbg(dev, "rx%u: client 0x%02x assigned alias 0x%02x at slot %u\n",
>   		rxport->nport, client->addr, alias, reg_idx);
>   
> -	return 0;
> +out_unlock:
> +	mutex_unlock(&rxport->aliased_addrs_lock);
> +	return ret;
>   }
>   
>   static void ub960_atr_detach_client(struct i2c_atr *atr, u32 chan_id,
> @@ -1062,6 +1070,8 @@ static void ub960_atr_detach_client(struct i2c_atr *atr, u32 chan_id,
>   	struct device *dev = &priv->client->dev;
>   	unsigned int reg_idx;
>   
> +	mutex_lock(&rxport->aliased_addrs_lock);
> +
>   	for (reg_idx = 0; reg_idx < UB960_MAX_PORT_ALIASES; reg_idx++) {
>   		if (rxport->aliased_addrs[reg_idx] == client->addr)
>   			break;
> @@ -1070,7 +1080,7 @@ static void ub960_atr_detach_client(struct i2c_atr *atr, u32 chan_id,
>   	if (reg_idx == UB960_MAX_PORT_ALIASES) {
>   		dev_err(dev, "rx%u: client 0x%02x is not mapped!\n",
>   			rxport->nport, client->addr);
> -		return;
> +		goto out_unlock;
>   	}
>   
>   	rxport->aliased_addrs[reg_idx] = 0;
> @@ -1079,6 +1089,9 @@ static void ub960_atr_detach_client(struct i2c_atr *atr, u32 chan_id,
>   
>   	dev_dbg(dev, "rx%u: client 0x%02x released at slot %u\n", rxport->nport,
>   		client->addr, reg_idx);
> +
> +out_unlock:
> +	mutex_unlock(&rxport->aliased_addrs_lock);
>   }
>   
>   static const struct i2c_atr_ops ub960_atr_ops = {
> @@ -3181,6 +3194,8 @@ static void ub960_rxport_free_ports(struct ub960_data *priv)
>   		fwnode_handle_put(rxport->source.ep_fwnode);
>   		fwnode_handle_put(rxport->ser.fwnode);
>   
> +		mutex_destroy(&rxport->aliased_addrs_lock);
> +
>   		kfree(rxport);
>   		priv->rxports[nport] = NULL;
>   	}
> @@ -3401,6 +3416,8 @@ static int ub960_parse_dt_rxport(struct ub960_data *priv, unsigned int nport,
>   	if (ret)
>   		goto err_put_remote_fwnode;
>   
> +	mutex_init(&rxport->aliased_addrs_lock);
> +
>   	return 0;
>   
>   err_put_remote_fwnode:
>