Messages in this thread | | | Subject | Re: [BUG] io_uring: defer logic based on shared data | From | Jens Axboe <> | Date | Fri, 25 Oct 2019 10:44:35 -0600 |
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On 10/25/19 10:40 AM, Pavel Begunkov wrote: > On 25/10/2019 19:32, Jens Axboe wrote: >> On 10/25/19 10:27 AM, Jens Axboe wrote: >>> 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. >> >> Here we go, patch 1: >> >> http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=f2a241f596ed9e12b7c8f960e79ccda8053ea294 >> >> patch 2: >> >> http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=b7d0297d2df5bfa0d1ecf9d6c66d23676751ef6a >> > 1. submit rqs (not yet completed) > 2. poll_list is empty, inflight = 0 > 3. async completed and placed into poll_list > > So, poll_list is not empty, but we won't get to polling again. > At least until someone submitted something.
But if they are issued, the will sit in ->poll_list as well. That list holds both "submitted, but pending" and completed entries.
-- Jens Axboe
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