mbox series

[0/2] cleanup patch

Message ID 20230922093842.2646157-1-haowenchao2@huawei.com
Headers show
Series cleanup patch | expand

Message

Wenchao Hao Sept. 22, 2023, 9:38 a.m. UTC 
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(-)

Comments

Wenchao Hao Sept. 24, 2023, 6:27 a.m. UTC | #1 
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;
>>   }
>>   
>>   /*
>
Wenchao Hao Sept. 24, 2023, 7:49 a.m. UTC | #2 
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;
}
Wenchao Hao Oct. 11, 2023, 12:37 p.m. UTC | #3 
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...