On 10/25/19 10:55 AM, Pavel Begunkov wrote: > 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! Glad we agree :-) >> + 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. Sure, I'll make that change and add your reviewed-by. Thanks! -- Jens Axboe
