linux-kernel - Re: [RFC PATCH] workqueue: fix cast warnings on i386

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Date:   Sun, 30 Apr 2023 21:42:04 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH] workqueue: fix cast warnings on i386

Hi Lai,

On 4/30/23 21:37, Lai Jiangshan wrote:
> On Sat, Apr 29, 2023 at 12:45 PM Randy Dunlap <rdunlap@...radead.org> wrote:
>>
>> Add casts to avoid int-to-pointer-cast warings on i386 or UML for i386:
>>
>> ../kernel/workqueue.c: In function ‘get_work_pwq’:
>> ../kernel/workqueue.c:713:24: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
>>   713 |                 return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
>>       |                        ^
>> ../kernel/workqueue.c: In function ‘get_work_pool’:
>> ../kernel/workqueue.c:741:25: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
>>   741 |                 return ((struct pool_workqueue *)
>>       |                         ^
>> ../kernel/workqueue.c: In function ‘get_work_pool_id’:
>> ../kernel/workqueue.c:763:25: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
>>   763 |                 return ((struct pool_workqueue *)
>>       |                         ^
>>
> 
> Hello, Randy
> 
> Both the type of the "data" and WORK_STRUCT_WQ_DATA_MASK are
> "unsigned long", so I don't think "(data & WORK_STRUCT_WQ_DATA_MASK)"
> needs to be converted to "unsigned long".
> 
>         WORK_STRUCT_FLAG_MASK   = (1UL << WORK_STRUCT_FLAG_BITS) - 1,
>         WORK_STRUCT_WQ_DATA_MASK = ~WORK_STRUCT_FLAG_MASK,
> 
> This simple fix might hide the real problem.

Thanks for replying.

Do you have any suggestions for how to eliminate these warnings on i386
and ARCH=um SUBARCH=i386?

> Thanks
> Lai.
> 
>> Fixes: e120153ddf86 ("workqueue: fix how cpu number is stored in work->data")
>> Fixes: 112202d9098a ("workqueue: rename cpu_workqueue to pool_workqueue")
>> Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
>> Cc: Tejun Heo <tj@...nel.org>
>> Cc: Lai Jiangshan <jiangshanlai@...il.com>
>> ---
>>  kernel/workqueue.c |    6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff -- a/kernel/workqueue.c b/kernel/workqueue.c
>> --- a/kernel/workqueue.c
>> +++ b/kernel/workqueue.c
>> @@ -710,7 +710,7 @@ static struct pool_workqueue *get_work_p
>>         unsigned long data = atomic_long_read(&work->data);
>>
>>         if (data & WORK_STRUCT_PWQ)
>> -               return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
>> +               return (void *)(unsigned long)(data & WORK_STRUCT_WQ_DATA_MASK);
>>         else
>>                 return NULL;
>>  }
>> @@ -739,7 +739,7 @@ static struct worker_pool *get_work_pool
>>
>>         if (data & WORK_STRUCT_PWQ)
>>                 return ((struct pool_workqueue *)
>> -                       (data & WORK_STRUCT_WQ_DATA_MASK))->pool;
>> +                       (unsigned long)(data & WORK_STRUCT_WQ_DATA_MASK))->pool;
>>
>>         pool_id = data >> WORK_OFFQ_POOL_SHIFT;
>>         if (pool_id == WORK_OFFQ_POOL_NONE)
>> @@ -761,7 +761,7 @@ static int get_work_pool_id(struct work_
>>
>>         if (data & WORK_STRUCT_PWQ)
>>                 return ((struct pool_workqueue *)
>> -                       (data & WORK_STRUCT_WQ_DATA_MASK))->pool->id;
>> +                       (unsigned long)(data & WORK_STRUCT_WQ_DATA_MASK))->pool->id;
>>
>>         return data >> WORK_OFFQ_POOL_SHIFT;
>>  }

-- 
~Randy