Re: Return value of __mm_populate

Re: Return value of __mm_populate

[Marco]

Adding in cc: lkml

Il 13/04/2013 14:14, Marco Stornelli ha scritto:
> Hi,
>
> I was seeing the code of __mm_populate (in -next) and I've got a doubt
> about the return value. The function __mlock_posix_error_return should
> return a proper error for mlock, converting the return value from
> __get_user_pages. It checks for EFAULT and ENOMEM. Actually
> __get_user_pages could return, in addition, ERESTARTSYS and EHWPOISON.
> So it seems to me that we could return to user space not expected value.
> I can't see them on the man page. In addition we shouldn't ever return
> ERESTARTSYS to the user space but EINTR. According to the man pages
> maybe we should return EAGAIN in these cases. Am I missing something?
>
> Thanks,
>
> Marco

Re: Return value of __mm_populate

[KOSAKI Motohiro]

(4/13/13 5:14 AM), Marco Stornelli wrote:
> Hi,
> 
> I was seeing the code of __mm_populate (in -next) and I've got a doubt 
> about the return value. The function __mlock_posix_error_return should 
> return a proper error for mlock, converting the return value from 
> __get_user_pages. It checks for EFAULT and ENOMEM. Actually 
> __get_user_pages could return, in addition, ERESTARTSYS and EHWPOISON. 

__get_user_pages doesn't return EHWPOISON if FOLL_HWPOISON is not specified.
I'm not expert ERESTARTSYS. I understand correctly, ERESTARTSYS is only returned
when signal received, and signal handling routine (e.g. do_signal) modify EIP and
hidden ERESTARTSYS from userland generically.


> So it seems to me that we could return to user space not expected value. 
> I can't see them on the man page. In addition we shouldn't ever return 
> ERESTARTSYS to the user space but EINTR. According to the man pages 
> maybe we should return EAGAIN in these cases. Am I missing something?

Re: Return value of __mm_populate

[Marco Stornelli]

Hi,

Il 14/04/2013 02:18, KOSAKI Motohiro ha scritto:
> (4/13/13 5:14 AM), Marco Stornelli wrote:
>> Hi,
>>
>> I was seeing the code of __mm_populate (in -next) and I've got a doubt
>> about the return value. The function __mlock_posix_error_return should
>> return a proper error for mlock, converting the return value from
>> __get_user_pages. It checks for EFAULT and ENOMEM. Actually
>> __get_user_pages could return, in addition, ERESTARTSYS and EHWPOISON.
>
> __get_user_pages doesn't return EHWPOISON if FOLL_HWPOISON is not specified.
> I'm not expert ERESTARTSYS. I understand correctly, ERESTARTSYS is only returned
> when signal received, and signal handling routine (e.g. do_signal) modify EIP and
> hidden ERESTARTSYS from userland generically.
>

Yep, you're right, the "magic" is inside the signal management. Thanks!!

Marco