Re: [PATCH v2] fs: replace the ki_complete two integer arguments with a single argument

[Jeff Moyer <jmoyer@redhat.com>]

Jeff Moyer <jmoyer@redhat.com> writes:

> Jens Axboe <axboe@kernel.dk> writes:
>
>> On 10/21/21 12:05 PM, Jeff Moyer wrote:
>>> 
>>>>> I'll follow up if there are issues.
>>> 
>>> s390 (big endian, 64 bit) is failing libaio test 21:
>>> 
>>> # harness/cases/21.p
>>> Expected -EAGAIN, got 4294967285
>>> 
>>> If I print out both res and res2 using %lx, you'll see what happened:
>>> 
>>> Expected -EAGAIN, got fffffff5,ffffffff
>>> 
>>> The sign extension is being split up.
>>
>> Funky, does it work if you apply this on top?
>>
>> diff --git a/fs/aio.c b/fs/aio.c
>> index 3674abc43788..c56437908339 100644
>> --- a/fs/aio.c
>> +++ b/fs/aio.c
>> @@ -1442,8 +1442,8 @@ static void aio_complete_rw(struct kiocb *kiocb, u64 res)
>>  	 * 32-bits of value at most for either value, bundle these up and
>>  	 * pass them in one u64 value.
>>  	 */
>> -	iocb->ki_res.res = lower_32_bits(res);
>> -	iocb->ki_res.res2 = upper_32_bits(res);
>> +	iocb->ki_res.res = (long) (res & 0xffffffff);
>> +	iocb->ki_res.res2 = (long) (res >> 32);
>>  	iocb_put(iocb);
>>  }
>
> I think you'll also need to clamp any ki_complete() call sites to 32
> bits (cast to int, or what have you).  Otherwise that sign extension
> will spill over into res2.
>
> fwiw, I tested with this:
>
> 	iocb->ki_res.res = (long)(int)lower_32_bits(res);
> 	iocb->ki_res.res2 = (long)(int)upper_32_bits(res);
>
> Coupled with the call site changes, that made things work for me.

This is all starting to feel like a minefield.  If you don't have any
concrete numbers to show that there is a speedup, I think we should
shelf this change.

-Jeff