[PATCH v2] driver core: Explicitly initialize struct member @data.have_async in __device_attach()

[PATCH v2] driver core: Explicitly initialize struct member @data.have_async in __device_attach()

[Zijun Hu]

From: Zijun Hu <quic_zijuhu@quicinc.com>

__device_attach() relies on compiler to implicitly initialize struct
member @data.have_async to avoid the member is used before initialization
but readers may not understand that, solved by explicitly initializing
@data.have_async as well as existing @data.want_async.

Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
---
Changes in v2:
- Remove both fix and stable tag
- Correct both title and commit messages
- Link to v1: https://lore.kernel.org/r/20240823-fix_have_async-v1-1-43a354b6614b@quicinc.com
---
 drivers/base/dd.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 9b745ba54de1..b0c44b0846aa 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -1021,6 +1021,7 @@ static int __device_attach(struct device *dev, bool allow_async)
 			.dev = dev,
 			.check_async = allow_async,
 			.want_async = false,
+			.have_async = false,
 		};
 
 		if (dev->parent)

---
base-commit: 87ee9981d1f86ee9b1623a46c7f9e4ac24461fe4
change-id: 20240823-fix_have_async-3a135618d91b

Best regards,
-- 
Zijun Hu <quic_zijuhu@quicinc.com>

Re: [PATCH v2] driver core: Explicitly initialize struct member @data.have_async in __device_attach()

[Dmitry Torokhov]

On Fri, Aug 23, 2024 at 08:00:14PM +0800, Zijun Hu wrote:
> From: Zijun Hu <quic_zijuhu@quicinc.com>
> 
> __device_attach() relies on compiler to implicitly initialize struct
> member @data.have_async to avoid the member is used before initialization
> but readers may not understand that, solved by explicitly initializing
> @data.have_async as well as existing @data.want_async.

I do not believe this is needed. We require kernel developers be
familiar with the language of choice for the kernel.

We have a ton of partial or empty structure initializers in the kernel.
If we count only empty non-static ones I see:

dtor@dtor-ws:~/kernel/work $ git grep '= \?{ \?};' | grep -v static | wc -l
5707

Rough count of partial initializers is (might be over eager and some
of them could be full ones, on the other hand it does not count
initializers that span multiple lines and start with opening brace
only):

dtor@dtor-ws:~/kernel/work $ git grep '= \?{ \..* };' | grep -v static | wc -l
1150

Are you planning to go through all of them and add complete
initializers? And keep adjusting them when structures will get extended?
For what gain?

There was no readers confusion, you wrote a tool for C static analysis
that did not follow C standard and gave you a false warning. Please fix
your tool instead.

> 
> Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
> ---
> Changes in v2:
> - Remove both fix and stable tag
> - Correct both title and commit messages
> - Link to v1: https://lore.kernel.org/r/20240823-fix_have_async-v1-1-43a354b6614b@quicinc.com
> ---
>  drivers/base/dd.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 9b745ba54de1..b0c44b0846aa 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -1021,6 +1021,7 @@ static int __device_attach(struct device *dev, bool allow_async)
>  			.dev = dev,
>  			.check_async = allow_async,
>  			.want_async = false,
> +			.have_async = false,
>  		};
>  
>  		if (dev->parent)
> 
> ---
> base-commit: 87ee9981d1f86ee9b1623a46c7f9e4ac24461fe4
> change-id: 20240823-fix_have_async-3a135618d91b
> 
> Best regards,
> -- 
> Zijun Hu <quic_zijuhu@quicinc.com>
> 

Thanks.

-- 
Dmitry

Re: [PATCH v2] driver core: Explicitly initialize struct member @data.have_async in __device_attach()

[Zijun Hu]

On 2024/8/23 23:55, Dmitry Torokhov wrote:
> On Fri, Aug 23, 2024 at 08:00:14PM +0800, Zijun Hu wrote:
>> From: Zijun Hu <quic_zijuhu@quicinc.com>
>>
>> __device_attach() relies on compiler to implicitly initialize struct
>> member @data.have_async to avoid the member is used before initialization
>> but readers may not understand that, solved by explicitly initializing
>> @data.have_async as well as existing @data.want_async.
> 
> I do not believe this is needed. We require kernel developers be
> familiar with the language of choice for the kernel.
> 
> We have a ton of partial or empty structure initializers in the kernel.
> If we count only empty non-static ones I see:
> 
> dtor@dtor-ws:~/kernel/work $ git grep '= \?{ \?};' | grep -v static | wc -l
> 5707
> 
> Rough count of partial initializers is (might be over eager and some
> of them could be full ones, on the other hand it does not count
> initializers that span multiple lines and start with opening brace
> only):
> 
> dtor@dtor-ws:~/kernel/work $ git grep '= \?{ \..* };' | grep -v static | wc -l
> 1150
> 
> Are you planning to go through all of them and add complete
> initializers? And keep adjusting them when structures will get extended?
> For what gain?
> 
actually, many partial initializers is proper, for example, we don't use
these fields that are implicitly initialized, for example, another usage
of the same same in the file drivers/base/dd.c.

no, let me take time to check if there are other usages in kernel tree
similar the one we discuss.

> There was no readers confusion, you wrote a tool for C static analysis
> that did not follow C standard and gave you a false warning. Please fix
> your tool instead.
> 
>>
>> Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
>> ---
>> Changes in v2:
>> - Remove both fix and stable tag
>> - Correct both title and commit messages
>> - Link to v1: https://lore.kernel.org/r/20240823-fix_have_async-v1-1-43a354b6614b@quicinc.com
>> ---
>>  drivers/base/dd.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
>> index 9b745ba54de1..b0c44b0846aa 100644
>> --- a/drivers/base/dd.c
>> +++ b/drivers/base/dd.c
>> @@ -1021,6 +1021,7 @@ static int __device_attach(struct device *dev, bool allow_async)
>>  			.dev = dev,
>>  			.check_async = allow_async,
>>  			.want_async = false,
>> +			.have_async = false,
>>  		};
>>  
>>  		if (dev->parent)
>>
>> ---
>> base-commit: 87ee9981d1f86ee9b1623a46c7f9e4ac24461fe4
>> change-id: 20240823-fix_have_async-3a135618d91b
>>
>> Best regards,
>> -- 
>> Zijun Hu <quic_zijuhu@quicinc.com>
>>
> 
> Thanks.
>