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. -- Yours sincerely, Pavel Begunkov
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