On 20/12/2020 19:34, Pavel Begunkov wrote:
> On 14/12/2020 15:49, Xiaoguang Wang wrote:
>> io_iopoll_complete() does not hold completion_lock to complete polled
>> io, so in io_wq_submit_work(), we can not call io_req_complete() directly,
>> to complete polled io, otherwise there maybe concurrent access to cqring,
>> defer_list, etc, which is not safe. Commit dad1b1242fd5 ("io_uring: always
>> let io_iopoll_complete() complete polled io") has fixed this issue, but
>> Pavel reported that IOPOLL apart from rw can do buf reg/unreg requests(
>> IORING_OP_PROVIDE_BUFFERS or IORING_OP_REMOVE_BUFFERS), so the fix is
>> not good.
>>
>> Given that io_iopoll_complete() is always called under uring_lock, so here
>> for polled io, we can also get uring_lock to fix this issue.
>
> This returns it to the state it was before fixing + mutex locking for
> IOPOLL, and it's much better than having it half-broken as it is now.
btw, comments are over 80, but that's minor.
>
> Cc: <stable@xxxxxxxxxxxxxxx> # 5.5+
> Reviewed-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
>
>>
>> Fixes: dad1b1242fd5 ("io_uring: always let io_iopoll_complete() complete polled io")
>> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
>> ---
>> fs/io_uring.c | 25 +++++++++++++++----------
>> 1 file changed, 15 insertions(+), 10 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index f53356ced5ab..eab3d2b7d232 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -6354,19 +6354,24 @@ static struct io_wq_work *io_wq_submit_work(struct io_wq_work *work)
>> }
>>
>> if (ret) {
>> + bool iopoll_enabled = req->ctx->flags & IORING_SETUP_IOPOLL;
>> +
>> /*
>> - * io_iopoll_complete() does not hold completion_lock to complete
>> - * polled io, so here for polled io, just mark it done and still let
>> - * io_iopoll_complete() complete it.
>> + * io_iopoll_complete() does not hold completion_lock to complete polled
>> + * io, so here for polled io, we can not call io_req_complete() directly,
>> + * otherwise there maybe concurrent access to cqring, defer_list, etc,
>> + * which is not safe. Given that io_iopoll_complete() is always called
>> + * under uring_lock, so here for polled io, we also get uring_lock to
>> + * complete it.
>> */
>> - if (req->ctx->flags & IORING_SETUP_IOPOLL) {
>> - struct kiocb *kiocb = &req->rw.kiocb;
>> + if (iopoll_enabled)
>> + mutex_lock(&req->ctx->uring_lock);
>>
>> - kiocb_done(kiocb, ret, NULL);
>> - } else {
>> - req_set_fail_links(req);
>> - io_req_complete(req, ret);
>> - }
>> + req_set_fail_links(req);
>> + io_req_complete(req, ret);
>> +
>> + if (iopoll_enabled)
>> + mutex_unlock(&req->ctx->uring_lock);
>> }
>>
>> return io_steal_work(req);
>>
>
--
Pavel Begunkov
