[PATCH] i2c: altera: Fix race between xfer_msg and isr thread

[PATCH] i2c: altera: Fix race between xfer_msg and isr thread

[Atsushi Nemoto]

Use a mutex to protect access to idev->msg_len, idev->buf, etc. which
are modified by both altr_i2c_xfer_msg() and altr_i2c_isr().

Signed-off-by: Atsushi Nemoto <atsushi.nemoto@sord.co.jp>
---
 drivers/i2c/busses/i2c-altera.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-altera.c b/drivers/i2c/busses/i2c-altera.c
index 20ef63820c77..3db7d77c5a1e 100644
--- a/drivers/i2c/busses/i2c-altera.c
+++ b/drivers/i2c/busses/i2c-altera.c
@@ -70,6 +70,7 @@
  * @isr_mask: cached copy of local ISR enables.
  * @isr_status: cached copy of local ISR status.
  * @lock: spinlock for IRQ synchronization.
+ * @mutex: mutex for IRQ thread.
  */
 struct altr_i2c_dev {
 	void __iomem *base;
@@ -86,6 +87,7 @@ struct altr_i2c_dev {
 	u32 isr_mask;
 	u32 isr_status;
 	spinlock_t lock;	/* IRQ synchronization */
+	struct mutex mutex;
 };
 
 static void
@@ -245,10 +247,11 @@ static irqreturn_t altr_i2c_isr(int irq, void *_dev)
 	struct altr_i2c_dev *idev = _dev;
 	u32 status = idev->isr_status;
 
+	mutex_lock(&idev->mutex);
 	if (!idev->msg) {
 		dev_warn(idev->dev, "unexpected interrupt\n");
 		altr_i2c_int_clear(idev, ALTR_I2C_ALL_IRQ);
-		return IRQ_HANDLED;
+		goto out;
 	}
 	read = (idev->msg->flags & I2C_M_RD) != 0;
 
@@ -301,6 +304,8 @@ static irqreturn_t altr_i2c_isr(int irq, void *_dev)
 		complete(&idev->msg_complete);
 		dev_dbg(idev->dev, "Message Complete\n");
 	}
+out:
+	mutex_unlock(&idev->mutex);
 
 	return IRQ_HANDLED;
 }
@@ -312,6 +317,7 @@ static int altr_i2c_xfer_msg(struct altr_i2c_dev *idev, struct i2c_msg *msg)
 	u32 value;
 	u8 addr = i2c_8bit_addr_from_msg(msg);
 
+	mutex_lock(&idev->mutex);
 	idev->msg = msg;
 	idev->msg_len = msg->len;
 	idev->buf = msg->buf;
@@ -336,6 +342,7 @@ static int altr_i2c_xfer_msg(struct altr_i2c_dev *idev, struct i2c_msg *msg)
 		altr_i2c_int_enable(idev, imask, true);
 		altr_i2c_fill_tx_fifo(idev);
 	}
+	mutex_unlock(&idev->mutex);
 
 	time_left = wait_for_completion_timeout(&idev->msg_complete,
 						ALTR_I2C_XFER_TIMEOUT);
@@ -410,6 +417,7 @@ static int altr_i2c_probe(struct platform_device *pdev)
 	idev->dev = &pdev->dev;
 	init_completion(&idev->msg_complete);
 	spin_lock_init(&idev->lock);
+	mutex_init(&idev->mutex);
 
 	val = device_property_read_u32(idev->dev, "fifo-size",
 				       &idev->fifo_size);
-- 
2.11.0

Re: [PATCH] i2c: altera: Fix race between xfer_msg and isr thread

[Thor Thayer]

On 4/9/20 8:06 PM, Atsushi Nemoto wrote:
> Use a mutex to protect access to idev->msg_len, idev->buf, etc. which
> are modified by both altr_i2c_xfer_msg() and altr_i2c_isr().
> 
> Signed-off-by: Atsushi Nemoto <atsushi.nemoto@sord.co.jp>
> ---

Acked-by: Thor Thayer <thor.thayer@linux.intel.com>

>   drivers/i2c/busses/i2c-altera.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-altera.c b/drivers/i2c/busses/i2c-altera.c
> index 20ef63820c77..3db7d77c5a1e 100644
> --- a/drivers/i2c/busses/i2c-altera.c
> +++ b/drivers/i2c/busses/i2c-altera.c
> @@ -70,6 +70,7 @@
>    * @isr_mask: cached copy of local ISR enables.
>    * @isr_status: cached copy of local ISR status.
>    * @lock: spinlock for IRQ synchronization.
> + * @mutex: mutex for IRQ thread.
>    */
>   struct altr_i2c_dev {
>   	void __iomem *base;
> @@ -86,6 +87,7 @@ struct altr_i2c_dev {
>   	u32 isr_mask;
>   	u32 isr_status;
>   	spinlock_t lock;	/* IRQ synchronization */
> +	struct mutex mutex;
>   };
>   
>   static void
> @@ -245,10 +247,11 @@ static irqreturn_t altr_i2c_isr(int irq, void *_dev)
>   	struct altr_i2c_dev *idev = _dev;
>   	u32 status = idev->isr_status;
>   
> +	mutex_lock(&idev->mutex);
>   	if (!idev->msg) {
>   		dev_warn(idev->dev, "unexpected interrupt\n");
>   		altr_i2c_int_clear(idev, ALTR_I2C_ALL_IRQ);
> -		return IRQ_HANDLED;
> +		goto out;
>   	}
>   	read = (idev->msg->flags & I2C_M_RD) != 0;
>   
> @@ -301,6 +304,8 @@ static irqreturn_t altr_i2c_isr(int irq, void *_dev)
>   		complete(&idev->msg_complete);
>   		dev_dbg(idev->dev, "Message Complete\n");
>   	}
> +out:
> +	mutex_unlock(&idev->mutex);
>   
>   	return IRQ_HANDLED;
>   }
> @@ -312,6 +317,7 @@ static int altr_i2c_xfer_msg(struct altr_i2c_dev *idev, struct i2c_msg *msg)
>   	u32 value;
>   	u8 addr = i2c_8bit_addr_from_msg(msg);
>   
> +	mutex_lock(&idev->mutex);
>   	idev->msg = msg;
>   	idev->msg_len = msg->len;
>   	idev->buf = msg->buf;
> @@ -336,6 +342,7 @@ static int altr_i2c_xfer_msg(struct altr_i2c_dev *idev, struct i2c_msg *msg)
>   		altr_i2c_int_enable(idev, imask, true);
>   		altr_i2c_fill_tx_fifo(idev);
>   	}
> +	mutex_unlock(&idev->mutex);
>   
>   	time_left = wait_for_completion_timeout(&idev->msg_complete,
>   						ALTR_I2C_XFER_TIMEOUT);
> @@ -410,6 +417,7 @@ static int altr_i2c_probe(struct platform_device *pdev)
>   	idev->dev = &pdev->dev;
>   	init_completion(&idev->msg_complete);
>   	spin_lock_init(&idev->lock);
> +	mutex_init(&idev->mutex);
>   
>   	val = device_property_read_u32(idev->dev, "fifo-size",
>   				       &idev->fifo_size);
> 

Re: [PATCH] i2c: altera: Fix race between xfer_msg and isr thread

[Wolfram Sang]

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On Fri, Apr 10, 2020 at 10:06:40AM +0900, Atsushi Nemoto wrote:
> Use a mutex to protect access to idev->msg_len, idev->buf, etc. which
> are modified by both altr_i2c_xfer_msg() and altr_i2c_isr().
> 
> Signed-off-by: Atsushi Nemoto <atsushi.nemoto@sord.co.jp>
> ---
>  drivers/i2c/busses/i2c-altera.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-altera.c b/drivers/i2c/busses/i2c-altera.c
> index 20ef63820c77..3db7d77c5a1e 100644
> --- a/drivers/i2c/busses/i2c-altera.c
> +++ b/drivers/i2c/busses/i2c-altera.c
> @@ -70,6 +70,7 @@
>   * @isr_mask: cached copy of local ISR enables.
>   * @isr_status: cached copy of local ISR status.
>   * @lock: spinlock for IRQ synchronization.
> + * @mutex: mutex for IRQ thread.

I think the name 'mutex' is too unspecific. (Same goes for 'lock' above
which is not part of your patch, obviously.)

>   */
>  struct altr_i2c_dev {
>  	void __iomem *base;
> @@ -86,6 +87,7 @@ struct altr_i2c_dev {
>  	u32 isr_mask;
>  	u32 isr_status;
>  	spinlock_t lock;	/* IRQ synchronization */
> +	struct mutex mutex;
>  };

Has it been checked if we really need both, the spinlock and the mutex?
From a glimpse, it looks like the spinlock became obsolete now.


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Re: [PATCH] i2c: altera: Fix race between xfer_msg and isr thread

[Atsushi Nemoto]

On Sun, 26 Apr 2020 10:30:31 +0200, Wolfram Sang <wsa@the-dreams.de> wrote:
>> --- a/drivers/i2c/busses/i2c-altera.c
>> +++ b/drivers/i2c/busses/i2c-altera.c
>> @@ -70,6 +70,7 @@
>>   * @isr_mask: cached copy of local ISR enables.
>>   * @isr_status: cached copy of local ISR status.
>>   * @lock: spinlock for IRQ synchronization.
>> + * @mutex: mutex for IRQ thread.
> 
> I think the name 'mutex' is too unspecific. (Same goes for 'lock' above
> which is not part of your patch, obviously.)

Then, how about 'isr_mutex' ?  Should I resend a patch with new name?

>>   */
>>  struct altr_i2c_dev {
>>  	void __iomem *base;
>> @@ -86,6 +87,7 @@ struct altr_i2c_dev {
>>  	u32 isr_mask;
>>  	u32 isr_status;
>>  	spinlock_t lock;	/* IRQ synchronization */
>> +	struct mutex mutex;
>>  };
> 
> Has it been checked if we really need both, the spinlock and the mutex?
> From a glimpse, it looks like the spinlock became obsolete now.

Yes, but just dropping the spinlock will leak two code pathes unlocked:

1. altr_i2c_int_enable() at end of altr_i2c_init()
2. altr_i2c_int_enable() just after wait_for_completion_timeout()

We can kill the spinlock by adding some more mutex_lock, but I think
that is not a _fix_ but _cleanup_, so I would like to do in another
patch.

---
Atsushi Nemoto

Re: [PATCH] i2c: altera: Fix race between xfer_msg and isr thread

[Atsushi Nemoto]

On Sun, 26 Apr 2020 19:39:16 +0900 (JST), Atsushi Nemoto <anemo@mba.ocn.ne.jp> wrote:
>>> + * @mutex: mutex for IRQ thread.
>> 
>> I think the name 'mutex' is too unspecific. (Same goes for 'lock' above
>> which is not part of your patch, obviously.)
> 
> Then, how about 'isr_mutex' ?  Should I resend a patch with new name?
> 
>>>   */
>>>  struct altr_i2c_dev {
>>>  	void __iomem *base;
>>> @@ -86,6 +87,7 @@ struct altr_i2c_dev {
>>>  	u32 isr_mask;
>>>  	u32 isr_status;
>>>  	spinlock_t lock;	/* IRQ synchronization */
>>> +	struct mutex mutex;
>>>  };
>> 
>> Has it been checked if we really need both, the spinlock and the mutex?
>> From a glimpse, it looks like the spinlock became obsolete now.
> 
> Yes, but just dropping the spinlock will leak two code pathes unlocked:
> 
> 1. altr_i2c_int_enable() at end of altr_i2c_init()
> 2. altr_i2c_int_enable() just after wait_for_completion_timeout()
> 
> We can kill the spinlock by adding some more mutex_lock, but I think
> that is not a _fix_ but _cleanup_, so I would like to do in another
> patch.

I will send a revised patch renaming 'mutex' to 'isr_mutex' (with
Thor's Acked-by line) and a patch to cleanup the spinlock.

---
Atsushi Nemoto