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

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Date:   Thu, 6 Feb 2020 12:56:57 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] io_uring: fix deferred req iovec leak

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.

-- 
Jens Axboe