On 4/5/22 9:57 PM, Ming Lei wrote: > On Tue, Apr 05, 2022 at 08:20:24PM -0600, Jens Axboe wrote: >> On 4/3/22 5:45 AM, Ming Lei wrote: >>> -EAGAIN still may return after io issue returns, and REQ_F_REISSUE is >>> set in io_complete_rw_iopoll(), but the req never gets chance to be handled. >>> io_iopoll_check doesn't handle this situation, and io hang can be caused. >>> >>> Current dm io polling may return -EAGAIN after bio submission is >>> returned, also blk-throttle might trigger this situation too. >> >> I don't think this is necessarily safe. Handling REQ_F_ISSUE from within >> the issue path is fine, as the request hasn't been submitted yet and >> hence we know that passed in structs are still stable. Once you hit it >> when polling for it, the io_uring_enter() call to submit requests has >> potentially already returned, and now we're in a second call where we >> are polling for requests. If we're doing eg an IORING_OP_READV, the >> original iovec may no longer be valid and we cannot safely re-import >> data associated with it. > > Yeah, this reissue is really not safe, thanks for the input. > > I guess the only way is to complete the cqe for this situation. At least if io_op_defs[req->opcode].needs_async_setup is true it isn't safe. But can't dm appropriately retry rather than bubble up the -EAGAIN off ->iopoll? -- Jens Axboe
