linux-kernel - Re: [PATCH 5/5] io_uring: add IORING_OP

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Message-Id: <57926544-3936-410f-ae0e-6eff266ea59c@app.fastmail.com>
Date:   Sat, 15 Jul 2023 09:12:13 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Jens Axboe" <axboe@...nel.dk>,
        "Christian Brauner" <brauner@...nel.org>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] io_uring: add IORING_OP_WAITID support

On Fri, Jul 14, 2023, at 22:14, Jens Axboe wrote:
> 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:
>>>>>> 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.

Sure, keeping that separate seem best.

Looking at what copy_siginfo_from_user_any() actually does, I don't
even think it's worth adapting copy_siginfo_to_user_any() for io_uring,
since it's already just a trivial wrapper, and adding another
argument would add more complexity overall than it saves.

      Arnd