Re: [PATCH 5/5] io_uring: add IORING_OP_WAITID support

[Jens Axboe <axboe@kernel.dk>]

On 7/14/23 12:33?PM, Arnd Bergmann wrote:
> On Fri, Jul 14, 2023, at 17:47, Christian Brauner wrote:
>> On Tue, Jul 11, 2023 at 04:18:13PM -0600, Jens Axboe wrote:
>>> On 7/11/23 3:22?PM, Jens Axboe wrote:
>>>> On 7/11/23 3:11?PM, Arnd Bergmann wrote:
> 
>>>>> Does this require argument conversion for compat tasks?
>>>>>
>>>>> Even without the rusage argument, I think the siginfo
>>>>> remains incompatible with 32-bit tasks, unfortunately.
>>>>
>>>> Hmm yes good point, if compat_siginfo and siginfo are different, then it
>>>> does need handling for that. Would be a trivial addition, I'll make that
>>>> change. Thanks Arnd!
>>>
>>> Should be fixed in the current version:
>>>
>>> https://git.kernel.dk/cgit/linux/commit/?h=io_uring-waitid&id=08f3dc9b7cedbd20c0f215f25c9a7814c6c601cc
>>
>> In kernel/signal.c in pidfd_send_signal() we have
>> copy_siginfo_from_user_any() it seems that a similar version
>> copy_siginfo_to_user_any() might be something to consider. We do have
>> copy_siginfo_to_user32() and copy_siginfo_to_user(). But I may lack
>> context why this wouldn't work here.
> 
> We could add a copy_siginfo_to_user_any(), but I think open-coding
> it is easier here, since the in_compat_syscall() check does not
> work inside of the io_uring kernel thread, it has to be
> "if (req->ctx->compat)" in order to match the wordsize of the task
> that started the request.

Yeah, unifying this stuff did cross my mind when adding another one.
Which I think could still be done, you'd just need to pass in a 'compat'
parameter similar to how it's done for iovec importing.

But if it's ok with everybody I'd rather do that as a cleanup post this.

> Using copy_siginfo_to_user32() and copy_siginfo_to_user() is
> probably a good idea though, it's often faster and less
> error-prone than writing each member separately.

I was just pattern matching on the other use cases. I'll take a look at
the siginfo copy helpers, thanks!

-- 
Jens Axboe