linux-kernel - Re: [PATCH] io_uring: store back buffer in case of failure

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Message-ID: <af2f7aa0-271f-ba70-8c6b-f6c6118e6f1f@gmail.com>
Date:   Wed, 16 Jun 2021 15:01:57 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Olivier Langlois <olivier@...llion01.com>,
        Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] io_uring: store back buffer in case of failure

On 6/16/21 2:42 PM, Olivier Langlois wrote:
> On Tue, 2021-06-15 at 15:51 -0600, Jens Axboe wrote:
>> Ditto for this one, don't see it in my email nor on the list.
>>
> I can resend you a private copy of this one but as Pavel pointed out,
> it contains fatal flaws.
> 
> So unless someone can tell me that the idea is interesting and has
> potential and can give me some a hint or 2 about how to address the
> challenges to fix the current flaws, it is pretty much a show stopper
> to me and I think that I am going to let it go...

It'd need to go through some other context, e.g. task context.
task_work_add() + custom handler would work, either buf-select
synchronisation can be reworked, but both would rather be
bulky and not great.

I'm more curious if we ever hit REQ_F_BUFFER_SELECTED branch in
io_clean_op(), because it would just drop the id on the floor...
It might use a WARN_ONCE.

-- 
Pavel Begunkov