From cd65869512ab5668a5d16f789bc4da1319c435c4 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 10 Sep 2021 11:19:14 -0600 Subject: [PATCH] io_uring: use iov_iter state save/restore helpers Get rid of the need to do re-expand and revert on an iterator when we encounter a short IO, or failure that warrants a retry. Use the new state save/restore helpers instead. We keep the iov_iter_state persistent across retries, if we need to restart the read or write operation. If there's a pending retry, the operation will always exit with the state correctly saved. Signed-off-by: Jens Axboe --- fs/io_uring.c | 82 ++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 61 insertions(+), 21 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 855ea544807f..25bda8a5a4e5 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -712,6 +712,7 @@ struct io_async_rw { struct iovec fast_iov[UIO_FASTIOV]; const struct iovec *free_iovec; struct iov_iter iter; + struct iov_iter_state iter_state; size_t bytes_done; struct wait_page_queue wpq; }; @@ -2608,8 +2609,7 @@ static bool io_resubmit_prep(struct io_kiocb *req) if (!rw) return !io_req_prep_async(req); - /* may have left rw->iter inconsistent on -EIOCBQUEUED */ - iov_iter_revert(&rw->iter, req->result - iov_iter_count(&rw->iter)); + iov_iter_restore(&rw->iter, &rw->iter_state); return true; } @@ -3310,12 +3310,17 @@ static int io_setup_async_rw(struct io_kiocb *req, const struct iovec *iovec, if (!force && !io_op_defs[req->opcode].needs_async_setup) return 0; if (!req->async_data) { + struct io_async_rw *iorw; + if (io_alloc_async_data(req)) { kfree(iovec); return -ENOMEM; } io_req_map_rw(req, iovec, fast_iov, iter); + iorw = req->async_data; + /* we've copied and mapped the iter, ensure state is saved */ + iov_iter_save_state(&iorw->iter, &iorw->iter_state); } return 0; } @@ -3334,6 +3339,7 @@ static inline int io_rw_prep_async(struct io_kiocb *req, int rw) iorw->free_iovec = iov; if (iov) req->flags |= REQ_F_NEED_CLEANUP; + iov_iter_save_state(&iorw->iter, &iorw->iter_state); return 0; } @@ -3437,19 +3443,28 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags) struct kiocb *kiocb = &req->rw.kiocb; struct iov_iter __iter, *iter = &__iter; struct io_async_rw *rw = req->async_data; - ssize_t io_size, ret, ret2; bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK; + struct iov_iter_state __state, *state; + ssize_t ret, ret2; if (rw) { iter = &rw->iter; + state = &rw->iter_state; + /* + * We come here from an earlier attempt, restore our state to + * match in case it doesn't. It's cheap enough that we don't + * need to make this conditional. + */ + iov_iter_restore(iter, state); iovec = NULL; } else { ret = io_import_iovec(READ, req, &iovec, iter, !force_nonblock); if (ret < 0) return ret; + state = &__state; + iov_iter_save_state(iter, state); } - io_size = iov_iter_count(iter); - req->result = io_size; + req->result = iov_iter_count(iter); /* Ensure we clear previously set non-block flag */ if (!force_nonblock) @@ -3463,7 +3478,7 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags) return ret ?: -EAGAIN; } - ret = rw_verify_area(READ, req->file, io_kiocb_ppos(kiocb), io_size); + ret = rw_verify_area(READ, req->file, io_kiocb_ppos(kiocb), req->result); if (unlikely(ret)) { kfree(iovec); return ret; @@ -3479,30 +3494,49 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags) /* no retry on NONBLOCK nor RWF_NOWAIT */ if (req->flags & REQ_F_NOWAIT) goto done; - /* some cases will consume bytes even on error returns */ - iov_iter_reexpand(iter, iter->count + iter->truncated); - iov_iter_revert(iter, io_size - iov_iter_count(iter)); ret = 0; } else if (ret == -EIOCBQUEUED) { goto out_free; - } else if (ret <= 0 || ret == io_size || !force_nonblock || + } else if (ret <= 0 || ret == req->result || !force_nonblock || (req->flags & REQ_F_NOWAIT) || !need_read_all(req)) { /* read all, failed, already did sync or don't want to retry */ goto done; } + /* + * Don't depend on the iter state matching what was consumed, or being + * untouched in case of error. Restore it and we'll advance it + * manually if we need to. + */ + iov_iter_restore(iter, state); + ret2 = io_setup_async_rw(req, iovec, inline_vecs, iter, true); if (ret2) return ret2; iovec = NULL; rw = req->async_data; - /* now use our persistent iterator, if we aren't already */ - iter = &rw->iter; + /* + * Now use our persistent iterator and state, if we aren't already. + * We've restored and mapped the iter to match. + */ + if (iter != &rw->iter) { + iter = &rw->iter; + state = &rw->iter_state; + } do { - io_size -= ret; + /* + * We end up here because of a partial read, either from + * above or inside this loop. Advance the iter by the bytes + * that were consumed. + */ + iov_iter_advance(iter, ret); + if (!iov_iter_count(iter)) + break; rw->bytes_done += ret; + iov_iter_save_state(iter, state); + /* if we can retry, do so with the callbacks armed */ if (!io_rw_should_retry(req)) { kiocb->ki_flags &= ~IOCB_WAITQ; @@ -3520,7 +3554,8 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags) return 0; /* we got some bytes, but not all. retry. */ kiocb->ki_flags &= ~IOCB_WAITQ; - } while (ret > 0 && ret < io_size); + iov_iter_restore(iter, state); + } while (ret > 0); done: kiocb_done(kiocb, ret, issue_flags); out_free: @@ -3543,19 +3578,24 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags) struct kiocb *kiocb = &req->rw.kiocb; struct iov_iter __iter, *iter = &__iter; struct io_async_rw *rw = req->async_data; - ssize_t ret, ret2, io_size; bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK; + struct iov_iter_state __state, *state; + ssize_t ret, ret2; if (rw) { iter = &rw->iter; + state = &rw->iter_state; + iov_iter_restore(iter, state); iovec = NULL; } else { ret = io_import_iovec(WRITE, req, &iovec, iter, !force_nonblock); if (ret < 0) return ret; + state = &__state; + iov_iter_save_state(iter, state); } - io_size = iov_iter_count(iter); - req->result = io_size; + req->result = iov_iter_count(iter); + ret2 = 0; /* Ensure we clear previously set non-block flag */ if (!force_nonblock) @@ -3572,7 +3612,7 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags) (req->flags & REQ_F_ISREG)) goto copy_iov; - ret = rw_verify_area(WRITE, req->file, io_kiocb_ppos(kiocb), io_size); + ret = rw_verify_area(WRITE, req->file, io_kiocb_ppos(kiocb), req->result); if (unlikely(ret)) goto out_free; @@ -3619,9 +3659,9 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags) kiocb_done(kiocb, ret2, issue_flags); } else { copy_iov: - /* some cases will consume bytes even on error returns */ - iov_iter_reexpand(iter, iter->count + iter->truncated); - iov_iter_revert(iter, io_size - iov_iter_count(iter)); + iov_iter_restore(iter, state); + if (ret2 > 0) + iov_iter_advance(iter, ret2); ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false); return ret ?: -EAGAIN; }