linux-kernel - Re: [PATCH] io_uring: fix deferred req iovec leak

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Date:   Thu, 6 Feb 2020 23:00:41 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] io_uring: fix deferred req iovec leak

On 06/02/2020 22:56, Jens Axboe wrote:
> On 2/6/20 10:16 AM, Pavel Begunkov wrote:
>> On 06/02/2020 20:04, Pavel Begunkov wrote:
>>> On 06/02/2020 19:51, Pavel Begunkov wrote:
>>>> After defer, a request will be prepared, that includes allocating iovec
>>>> if needed, and then submitted through io_wq_submit_work() but not custom
>>>> handler (e.g. io_rw_async()/io_sendrecv_async()). However, it'll leak
>>>> iovec, as it's in io-wq and the code goes as follows:
>>>>
>>>> io_read() {
>>>> 	if (!io_wq_current_is_worker())
>>>> 		kfree(iovec);
>>>> }
>>>>
>>>> Put all deallocation logic in io_{read,write,send,recv}(), which will
>>>> leave the memory, if going async with -EAGAIN.
>>>>
>>> Interestingly, this will fail badly if it returns -EAGAIN from io-wq context.
>>> Apparently, I need to do v2.
>>>
>> Or not...
>> Jens, can you please explain what's with the -EAGAIN handling in
>> io_wq_submit_work()? Checking the code, it seems neither of
>> read/write/recv/send can return -EAGAIN from async context (i.e.
>> force_nonblock=false). Are there other ops that can do it?
> 
> Nobody should return -EAGAIN with force_nonblock=false, they should
> end the io_kiocb inline for that.
> 

If so for those 4, then the patch should work well.

-- 
Pavel Begunkov



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