linux-kernel - Re: [BUG] io_uring: defer logic based on shared data

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Message-ID: <96446fe1-4f32-642b-7100-ebfa291d7127@kernel.dk>
Date:   Fri, 25 Oct 2019 10:27:50 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [BUG] io_uring: defer logic based on shared data

On 10/25/19 10:21 AM, Pavel Begunkov wrote:
> On 25/10/2019 19:03, Jens Axboe wrote:
>> On 10/25/19 3:55 AM, Pavel Begunkov wrote:
>>> I found 2 problems with __io_sequence_defer().
>>>
>>> 1. it uses @sq_dropped, but doesn't consider @cq_overflow
>>> 2. @sq_dropped and @cq_overflow are write-shared with userspace, so
>>> it can be maliciously changed.
>>>
>>> see sent liburing test (test/defer *_hung()), which left an unkillable
>>> process for me
>>
>> OK, how about the below. I'll split this in two, as it's really two
>> separate fixes.
> cached_sq_dropped is good, but I was concerned about cached_cq_overflow.
> io_cqring_fill_event() can be called in async, so shouldn't we do some
> synchronisation then?

We should probably make it an atomic just to be on the safe side, I'll
update the series.

-- 
Jens Axboe