[PATCH 0/2] cleanup patch

[PATCH 0/2] cleanup patch

[Wenchao Hao]

This is a cleanup patchset, no logic changed.

The first patch just cleanup scsi_dev_queue_ready();
The second patch add comment for target_destroy callback of
scsi_host_template to tell it is called in atomic context.

Wenchao Hao (2):
  scsi: core: cleanup scsi_dev_queue_ready()
  scsi: Add comment of target_destroy in scsi_host_template

 drivers/scsi/scsi_lib.c  | 35 ++++++++++++++++++-----------------
 include/scsi/scsi_host.h |  3 +++
 2 files changed, 21 insertions(+), 17 deletions(-)

-- 
2.32.0

[PATCH 1/2] scsi: core: cleanup scsi_dev_queue_ready()

[Wenchao Hao]

This is just a cleanup for scsi_dev_queue_ready() to avoid
redundant goto and if statement, it did not change the origin
logic.

Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
---
 drivers/scsi/scsi_lib.c | 35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index ca5eb058d5c7..f3e388127dbd 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1254,28 +1254,29 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
 	int token;
 
 	token = sbitmap_get(&sdev->budget_map);
-	if (atomic_read(&sdev->device_blocked)) {
-		if (token < 0)
-			goto out;
+	if (token < 0)
+		return -1;
 
-		if (scsi_device_busy(sdev) > 1)
-			goto out_dec;
+	/*
+	 * device_blocked is not set at mostly time, so check it first
+	 * and return token when it is not set.
+	 */
+	if (!atomic_read(&sdev->device_blocked))
+		return token;
 
-		/*
-		 * unblock after device_blocked iterates to zero
-		 */
-		if (atomic_dec_return(&sdev->device_blocked) > 0)
-			goto out_dec;
-		SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
-				   "unblocking device at zero depth\n"));
+	/*
+	 * unblock after device_blocked iterates to zero
+	 */
+	if (scsi_device_busy(sdev) > 1 ||
+	    atomic_dec_return(&sdev->device_blocked) > 0) {
+		sbitmap_put(&sdev->budget_map, token);
+		return -1;
 	}
 
+	SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
+			 "unblocking device at zero depth\n"));
+
 	return token;
-out_dec:
-	if (token >= 0)
-		sbitmap_put(&sdev->budget_map, token);
-out:
-	return -1;
 }
 
 /*
-- 
2.32.0

[PATCH 2/2] scsi: Add comment of target_destroy in scsi_host_template

[Wenchao Hao]

Add comment to tell callback function target_destroy of
scsi_host_template is called in atomic context.

Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
---
 include/scsi/scsi_host.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 49f768d0ff37..a72248fa5adf 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -245,6 +245,9 @@ struct scsi_host_template {
 	 * midlayer calls this point so that the driver may deallocate
 	 * and terminate any references to the target.
 	 *
+	 * Note: this callback in called with spin_lock held, so donot
+	 * call functions might cause schedule
+	 *
 	 * Status: OPTIONAL
 	 */
 	void (* target_destroy)(struct scsi_target *);
-- 
2.32.0

Re: [PATCH 1/2] scsi: core: cleanup scsi_dev_queue_ready()

[Damien Le Moal]

On 2023/09/22 2:38, Wenchao Hao wrote:
> This is just a cleanup for scsi_dev_queue_ready() to avoid
> redundant goto and if statement, it did not change the origin
> logic.
> 
> Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
> ---
>  drivers/scsi/scsi_lib.c | 35 ++++++++++++++++++-----------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index ca5eb058d5c7..f3e388127dbd 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1254,28 +1254,29 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
>  	int token;
>  
>  	token = sbitmap_get(&sdev->budget_map);
> -	if (atomic_read(&sdev->device_blocked)) {
> -		if (token < 0)
> -			goto out;
> +	if (token < 0)
> +		return -1;

This is changing how this function works...

>  
> -		if (scsi_device_busy(sdev) > 1)
> -			goto out_dec;
> +	/*
> +	 * device_blocked is not set at mostly time, so check it first
> +	 * and return token when it is not set.
> +	 */
> +	if (!atomic_read(&sdev->device_blocked))
> +		return token;

...because you reversed the tests order.

>  
> -		/*
> -		 * unblock after device_blocked iterates to zero
> -		 */
> -		if (atomic_dec_return(&sdev->device_blocked) > 0)
> -			goto out_dec;
> -		SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
> -				   "unblocking device at zero depth\n"));
> +	/*
> +	 * unblock after device_blocked iterates to zero
> +	 */
> +	if (scsi_device_busy(sdev) > 1 ||
> +	    atomic_dec_return(&sdev->device_blocked) > 0) {

And here too, you are changing how the function works. The atomic_dec may not be
done if the first condition is true.

> +		sbitmap_put(&sdev->budget_map, token);
> +		return -1;
>  	}
>  
> +	SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
> +			 "unblocking device at zero depth\n"));
> +
>  	return token;
> -out_dec:
> -	if (token >= 0)
> -		sbitmap_put(&sdev->budget_map, token);
> -out:
> -	return -1;
>  }
>  
>  /*

-- 
Damien Le Moal
Western Digital Research

Re: [PATCH 2/2] scsi: Add comment of target_destroy in scsi_host_template

[Bart Van Assche]

On 9/22/23 02:38, Wenchao Hao wrote:
> Add comment to tell callback function target_destroy of
> scsi_host_template is called in atomic context.
> 
> Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
> ---
>   include/scsi/scsi_host.h | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
> index 49f768d0ff37..a72248fa5adf 100644
> --- a/include/scsi/scsi_host.h
> +++ b/include/scsi/scsi_host.h
> @@ -245,6 +245,9 @@ struct scsi_host_template {
>   	 * midlayer calls this point so that the driver may deallocate
>   	 * and terminate any references to the target.
>   	 *
> +	 * Note: this callback in called with spin_lock held, so donot
> +	 * call functions might cause schedule
> +	 *

This comment should mention which spinlock is held.

Thanks,

Bart.

Re: [PATCH 1/2] scsi: core: cleanup scsi_dev_queue_ready()

[Wenchao Hao]

On 2023/9/22 20:50, Damien Le Moal wrote:
> On 2023/09/22 2:38, Wenchao Hao wrote:
>> This is just a cleanup for scsi_dev_queue_ready() to avoid
>> redundant goto and if statement, it did not change the origin
>> logic.
>>
>> Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
>> ---
>>   drivers/scsi/scsi_lib.c | 35 ++++++++++++++++++-----------------
>>   1 file changed, 18 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>> index ca5eb058d5c7..f3e388127dbd 100644
>> --- a/drivers/scsi/scsi_lib.c
>> +++ b/drivers/scsi/scsi_lib.c
>> @@ -1254,28 +1254,29 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
>>   	int token;
>>   
>>   	token = sbitmap_get(&sdev->budget_map);
>> -	if (atomic_read(&sdev->device_blocked)) {
>> -		if (token < 0)
>> -			goto out;
>> +	if (token < 0)
>> +		return -1;
> 
> This is changing how this function works...
>

I don't think so...
The origin function flow:

static inline int scsi_dev_queue_ready(struct request_queue *q,
				  struct scsi_device *sdev)
{
	...
	token = sbitmap_get(&sdev->budget_map);
	if (atomic_read(&sdev->device_blocked)) {
		if (token < 0)
			goto out;
	}
	return token;
out:
	return -1
}

If the token is less than 0, it would always return -1. So we can found
it's not necessary to check token after atomic_read().
  
>>   
>> -		if (scsi_device_busy(sdev) > 1)
>> -			goto out_dec;
>> +	/*
>> +	 * device_blocked is not set at mostly time, so check it first
>> +	 * and return token when it is not set.
>> +	 */
>> +	if (!atomic_read(&sdev->device_blocked))
>> +		return token;
> 
> ...because you reversed the tests order.

As explained in comment, the device_blocked is not set at mostly time,
so when it's not set, just return the token.

>>   
>> -		/*
>> -		 * unblock after device_blocked iterates to zero
>> -		 */
>> -		if (atomic_dec_return(&sdev->device_blocked) > 0)
>> -			goto out_dec;
>> -		SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
>> -				   "unblocking device at zero depth\n"));
>> +	/*
>> +	 * unblock after device_blocked iterates to zero
>> +	 */
>> +	if (scsi_device_busy(sdev) > 1 ||
>> +	    atomic_dec_return(&sdev->device_blocked) > 0) {
> 
> And here too, you are changing how the function works. The atomic_dec may not be
> done if the first condition is true.
> 

the origin flow would not call atomic_dec_return() too when condition
"scsi_device_busy(sdev) > 1" is true like following:

static inline int scsi_dev_queue_ready(struct request_queue *q,
				  struct scsi_device *sdev)
{
	...
	if (atomic_read(&sdev->device_blocked)) {
		if (scsi_device_busy(sdev) > 1)
			goto out_dec;

		/*
		 * unblock after device_blocked iterates to zero
		 */
		if (atomic_dec_return(&sdev->device_blocked) > 0)
			goto out_dec;
		SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
				   "unblocking device at zero depth\n"));
	}
	return token;
out_dec:
	if (token >= 0)
		sbitmap_put(&sdev->budget_map, token);
out:
	return -1;
}

Here is the function before and after my change:

The old function:
static inline int scsi_dev_queue_ready(struct request_queue *q,
				  struct scsi_device *sdev)
{
	int token;

	token = sbitmap_get(&sdev->budget_map);
	if (token < 0)
		return -1;

	/*
	 * device_blocked is not set at mostly time, so check it first
	 * and return token when it is not set.
	 */
	if (!atomic_read(&sdev->device_blocked))
		return token;

	/*
	 * unblock after device_blocked iterates to zero
	 */
	if (scsi_device_busy(sdev) > 1 ||
	    atomic_dec_return(&sdev->device_blocked) > 0) {
		sbitmap_put(&sdev->budget_map, token);
		return -1;
	}

	SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
			 "unblocking device at zero depth\n"));

	return token;
}

Function after my change:

static inline int scsi_dev_queue_ready(struct request_queue *q,
				  struct scsi_device *sdev)
{
	int token;

	token = sbitmap_get(&sdev->budget_map);
	if (token < 0)
		return -1;

	/*
	 * device_blocked is not set at mostly time, so check it first
	 * and return token when it is not set.
	 */
	if (!atomic_read(&sdev->device_blocked))
		return token;

	/*
	 * unblock after device_blocked iterates to zero
	 */
	if (scsi_device_busy(sdev) > 1 ||
	    atomic_dec_return(&sdev->device_blocked) > 0) {
		sbitmap_put(&sdev->budget_map, token);
		return -1;
	}

	SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
			 "unblocking device at zero depth\n"));

	return token;
}

I think it looks more clear and readable than before.


>> +		sbitmap_put(&sdev->budget_map, token);
>> +		return -1;
>>   	}
>>   
>> +	SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
>> +			 "unblocking device at zero depth\n"));
>> +
>>   	return token;
>> -out_dec:
>> -	if (token >= 0)
>> -		sbitmap_put(&sdev->budget_map, token);
>> -out:
>> -	return -1;
>>   }
>>   
>>   /*
> 

Re: [PATCH 2/2] scsi: Add comment of target_destroy in scsi_host_template

[Wenchao Hao]

On 2023/9/22 22:53, Bart Van Assche wrote:
> On 9/22/23 02:38, Wenchao Hao wrote:
>> Add comment to tell callback function target_destroy of
>> scsi_host_template is called in atomic context.
>>
>> Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
>> ---
>>   include/scsi/scsi_host.h | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
>> index 49f768d0ff37..a72248fa5adf 100644
>> --- a/include/scsi/scsi_host.h
>> +++ b/include/scsi/scsi_host.h
>> @@ -245,6 +245,9 @@ struct scsi_host_template {
>>        * midlayer calls this point so that the driver may deallocate
>>        * and terminate any references to the target.
>>        *
>> +     * Note: this callback in called with spin_lock held, so donot
>> +     * call functions might cause schedule
>> +     *
> 
> This comment should mention which spinlock is held.
> 

Would update, thanks for your review suggestion.

> Thanks,
> 
> Bart.
> 
> 

Re: [PATCH 1/2] scsi: core: cleanup scsi_dev_queue_ready()

[Wenchao Hao]

On 2023/9/24 14:27, Wenchao Hao wrote:
> On 2023/9/22 20:50, Damien Le Moal wrote:
>> On 2023/09/22 2:38, Wenchao Hao wrote:
>>> This is just a cleanup for scsi_dev_queue_ready() to avoid
>>> redundant goto and if statement, it did not change the origin
>>> logic.
>>>
>>> Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
>>> ---
>>>   drivers/scsi/scsi_lib.c | 35 ++++++++++++++++++-----------------
>>>   1 file changed, 18 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>>> index ca5eb058d5c7..f3e388127dbd 100644
>>> --- a/drivers/scsi/scsi_lib.c
>>> +++ b/drivers/scsi/scsi_lib.c
>>> @@ -1254,28 +1254,29 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
>>>       int token;
>>>       token = sbitmap_get(&sdev->budget_map);
>>> -    if (atomic_read(&sdev->device_blocked)) {
>>> -        if (token < 0)
>>> -            goto out;
>>> +    if (token < 0)
>>> +        return -1;
>>
>> This is changing how this function works...
>>
> 
> I don't think so...
> The origin function flow:
> 
> static inline int scsi_dev_queue_ready(struct request_queue *q,
>                    struct scsi_device *sdev)
> {
>      ...
>      token = sbitmap_get(&sdev->budget_map);
>      if (atomic_read(&sdev->device_blocked)) {
>          if (token < 0)
>              goto out;
>      }
>      return token;
> out:
>      return -1
> }
> 
> If the token is less than 0, it would always return -1. So we can found
> it's not necessary to check token after atomic_read().
> 
>>> -        if (scsi_device_busy(sdev) > 1)
>>> -            goto out_dec;
>>> +    /*
>>> +     * device_blocked is not set at mostly time, so check it first
>>> +     * and return token when it is not set.
>>> +     */
>>> +    if (!atomic_read(&sdev->device_blocked))
>>> +        return token;
>>
>> ...because you reversed the tests order.
> 
> As explained in comment, the device_blocked is not set at mostly time,
> so when it's not set, just return the token.
> 
>>> -        /*
>>> -         * unblock after device_blocked iterates to zero
>>> -         */
>>> -        if (atomic_dec_return(&sdev->device_blocked) > 0)
>>> -            goto out_dec;
>>> -        SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
>>> -                   "unblocking device at zero depth\n"));
>>> +    /*
>>> +     * unblock after device_blocked iterates to zero
>>> +     */
>>> +    if (scsi_device_busy(sdev) > 1 ||
>>> +        atomic_dec_return(&sdev->device_blocked) > 0) {
>>
>> And here too, you are changing how the function works. The atomic_dec may not be
>> done if the first condition is true.
>>
> 
> the origin flow would not call atomic_dec_return() too when condition
> "scsi_device_busy(sdev) > 1" is true like following:
> 
> static inline int scsi_dev_queue_ready(struct request_queue *q,
>                    struct scsi_device *sdev)
> {
>      ...
>      if (atomic_read(&sdev->device_blocked)) {
>          if (scsi_device_busy(sdev) > 1)
>              goto out_dec;
> 
>          /*
>           * unblock after device_blocked iterates to zero
>           */
>          if (atomic_dec_return(&sdev->device_blocked) > 0)
>              goto out_dec;
>          SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
>                     "unblocking device at zero depth\n"));
>      }
>      return token;
> out_dec:
>      if (token >= 0)
>          sbitmap_put(&sdev->budget_map, token);
> out:
>      return -1;
> }
> 
> Here is the function before and after my change:
> 
> The old function:
> static inline int scsi_dev_queue_ready(struct request_queue *q,
>                    struct scsi_device *sdev)
> {
>      int token;
> 
>      token = sbitmap_get(&sdev->budget_map);
>      if (token < 0)
>          return -1;
> 
>      /*
>       * device_blocked is not set at mostly time, so check it first
>       * and return token when it is not set.
>       */
>      if (!atomic_read(&sdev->device_blocked))
>          return token;
> 
>      /*
>       * unblock after device_blocked iterates to zero
>       */
>      if (scsi_device_busy(sdev) > 1 ||
>          atomic_dec_return(&sdev->device_blocked) > 0) {
>          sbitmap_put(&sdev->budget_map, token);
>          return -1;
>      }
> 
>      SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
>               "unblocking device at zero depth\n"));
> 
>      return token;
> }
> 

Sorry, I paste wrong for old function, the old function is:

static inline int scsi_dev_queue_ready(struct request_queue *q,
				  struct scsi_device *sdev)
{
	int token;

	token = sbitmap_get(&sdev->budget_map);
	if (atomic_read(&sdev->device_blocked)) {
		if (token < 0)
			goto out;

		if (scsi_device_busy(sdev) > 1)
			goto out_dec;

		/*
		 * unblock after device_blocked iterates to zero
		 */
		if (atomic_dec_return(&sdev->device_blocked) > 0)
			goto out_dec;
		SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
				   "unblocking device at zero depth\n"));
	}

	return token;
out_dec:
	if (token >= 0)
		sbitmap_put(&sdev->budget_map, token);
out:
	return -1;
}

Re: [PATCH 1/2] scsi: core: cleanup scsi_dev_queue_ready()

[Wenchao Hao]

On 2023/9/24 14:27, Wenchao Hao wrote:
> On 2023/9/22 20:50, Damien Le Moal wrote:
>> On 2023/09/22 2:38, Wenchao Hao wrote:
>>> This is just a cleanup for scsi_dev_queue_ready() to avoid
>>> redundant goto and if statement, it did not change the origin
>>> logic.
>>>
>>> Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
>>> ---
>>>   drivers/scsi/scsi_lib.c | 35 ++++++++++++++++++-----------------
>>>   1 file changed, 18 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>>> index ca5eb058d5c7..f3e388127dbd 100644
>>> --- a/drivers/scsi/scsi_lib.c
>>> +++ b/drivers/scsi/scsi_lib.c
>>> @@ -1254,28 +1254,29 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
>>>       int token;
>>>       token = sbitmap_get(&sdev->budget_map);
>>> -    if (atomic_read(&sdev->device_blocked)) {
>>> -        if (token < 0)
>>> -            goto out;
>>> +    if (token < 0)
>>> +        return -1;
>>
>> This is changing how this function works...
>>
> 
> I don't think so...
> The origin function flow:
> 
> static inline int scsi_dev_queue_ready(struct request_queue *q,
>                    struct scsi_device *sdev)
> {
>      ...
>      token = sbitmap_get(&sdev->budget_map);
>      if (atomic_read(&sdev->device_blocked)) {
>          if (token < 0)
>              goto out;
>      }
>      return token;
> out:
>      return -1
> }
> 
> If the token is less than 0, it would always return -1. So we can found
> it's not necessary to check token after atomic_read().
> 
>>> -        if (scsi_device_busy(sdev) > 1)
>>> -            goto out_dec;
>>> +    /*
>>> +     * device_blocked is not set at mostly time, so check it first
>>> +     * and return token when it is not set.
>>> +     */
>>> +    if (!atomic_read(&sdev->device_blocked))
>>> +        return token;
>>
>> ...because you reversed the tests order.
> 
> As explained in comment, the device_blocked is not set at mostly time,
> so when it's not set, just return the token.
> 

Friendly ping...