On 25/10/2019 19:44, Jens Axboe wrote: > 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. > Missed it, then should work. Thanks! > + ret = iters = 0; A small suggestion, could we just initialise it in declaration to be a bit more concise? e.g. int ret = 0, iters = 0; Reviewed-by: Pavel Begunkov <asml.silence@xxxxxxxxx> And let me test it as both patches are ready. -- Yours sincerely, Pavel Begunkov
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