linux-kernel - Re: [GIT PULL] io_uring updates for 5.10-rc1

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Message-ID: <7f2c7699-b8f4-3b50-d1c9-beeb429e32e4@kernel.dk>
Date:   Tue, 13 Oct 2020 15:00:56 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     io-uring <io-uring@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] io_uring updates for 5.10-rc1

On 10/13/20 2:49 PM, Rasmus Villemoes wrote:
> On 13/10/2020 21.49, Jens Axboe wrote:
>> On 10/13/20 1:46 PM, Linus Torvalds wrote:
>>> On Mon, Oct 12, 2020 at 6:46 AM Jens Axboe <axboe@...nel.dk> wrote:
>>>>
>>>> Here are the io_uring updates for 5.10.
>>>
>>> Very strange. My clang build gives a warning I've never seen before:
>>>
>>>    /tmp/io_uring-dd40c4.s:26476: Warning: ignoring changed section
>>> attributes for .data..read_mostly
>>>
>>> and looking at what clang generates for the *.s file, it seems to be
>>> the "section" line in:
>>>
>>>         .type   io_op_defs,@object      # @io_op_defs
>>>         .section        .data..read_mostly,"a",@progbits
>>>         .p2align        4
>>>
>>> I think it's the combination of "const" and "__read_mostly".
>>>
>>> I think the warning is sensible: how can a piece of data be both
>>> "const" and "__read_mostly"? If it's "const", then it's not "mostly"
>>> read - it had better be _always_ read.
>>>
>>> I'm letting it go, and I've pulled this (gcc doesn't complain), but
>>> please have a look.
>>
>> Huh weird, I'll take a look. FWIW, the construct isn't unique across
>> the kernel.
> 
> Citation needed. There's lots of "pointer to const foo" stuff declared
> as __read_mostly, but I can't find any objects that are themselves both
> const and __read_mostly. Other than that io_op_defs and io_uring_fops now.

You are right, they are all pointers, so not the same. I'll just revert
the patch.

-- 
Jens Axboe