On 12/8/20 12:24 PM, Pavel Begunkov wrote: > On 08/12/2020 19:17, Jens Axboe wrote: >> On 12/8/20 12:12 PM, Pavel Begunkov wrote: >>> On 07/12/2020 16:28, Jens Axboe wrote: >>>> On Sun, Dec 6, 2020 at 3:26 PM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote: >>>>> From: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx> >>>>> >>>>> The reason is that once we got a non EAGAIN error in io_wq_submit_work(), >>>>> we'll complete req by calling io_req_complete(), which will hold completion_lock >>>>> to call io_commit_cqring(), but for polled io, io_iopoll_complete() won't >>>>> hold completion_lock to call io_commit_cqring(), then there maybe concurrent >>>>> access to ctx->defer_list, double free may happen. >>>>> >>>>> To fix this bug, we always let io_iopoll_complete() complete polled io. >>>> >>>> This patch is causing hangs with iopoll testing, if you end up getting >>>> -EAGAIN on request submission. I've dropped it. >>> >>> I fail to understand without debugging how does it happen, especially since >>> it shouldn't even get out of the while in io_wq_submit_work(). Is that >>> something obvious I've missed? >> >> I didn't have time to look into it, and haven't yet, just reporting that >> it very reliably fails (and under what conditions). > > Yeah, I get it, asked just in case. > I'll see what's going on if Xiaoguang wouldn't handle it before. Should be trivial to reproduce on eg nvme by doing: echo mq-deadline > /sys/block/nvme0n1/queue/scheduler echo 2 > /sys/block/nvme0n1/queue/nr_requests and then run test/iopoll on that device. I'll try and take a look tomorrow unless someone beats me to it. -- Jens Axboe
