From 8fb0f47a9d7acf620d0fd97831b69da9bc5e22ed Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 10 Sep 2021 11:18:36 -0600 Subject: iov_iter: add helper to save iov_iter state In an ideal world, when someone is passed an iov_iter and returns X bytes, then X bytes would have been consumed/advanced from the iov_iter. But we have use cases that always consume the entire iterator, a few examples of that are iomap and bdev O_DIRECT. This means we cannot rely on the state of the iov_iter once we've called ->read_iter() or ->write_iter(). This would be easier if we didn't always have to deal with truncate of the iov_iter, as rewinding would be trivial without that. We recently added a commit to track the truncate state, but that grew the iov_iter by 8 bytes and wasn't the best solution. Implement a helper to save enough of the iov_iter state to sanely restore it after we've called the read/write iterator helpers. This currently only works for IOVEC/BVEC/KVEC as that's all we need, support for other iterator types are left as an exercise for the reader. Link: https://lore.kernel.org/linux-fsdevel/CAHk-=wiacKV4Gh-MYjteU0LwNBSGpWrK-Ov25HdqB1ewinrFPg@mail.gmail.com/ Signed-off-by: Jens Axboe --- include/linux/uio.h | 15 +++++++++++++++ lib/iov_iter.c | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 51 insertions(+) diff --git a/include/linux/uio.h b/include/linux/uio.h index 5265024e8b90..984c4ab74859 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -27,6 +27,12 @@ enum iter_type { ITER_DISCARD, }; +struct iov_iter_state { + size_t iov_offset; + size_t count; + unsigned long nr_segs; +}; + struct iov_iter { u8 iter_type; bool data_source; @@ -55,6 +61,14 @@ static inline enum iter_type iov_iter_type(const struct iov_iter *i) return i->iter_type; } +static inline void iov_iter_save_state(struct iov_iter *iter, + struct iov_iter_state *state) +{ + state->iov_offset = iter->iov_offset; + state->count = iter->count; + state->nr_segs = iter->nr_segs; +} + static inline bool iter_is_iovec(const struct iov_iter *i) { return iov_iter_type(i) == ITER_IOVEC; @@ -233,6 +247,7 @@ ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages, ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, struct page ***pages, size_t maxsize, size_t *start); int iov_iter_npages(const struct iov_iter *i, int maxpages); +void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state); const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags); diff --git a/lib/iov_iter.c b/lib/iov_iter.c index f2d50d69a6c3..755c10c5138c 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -1972,3 +1972,39 @@ int import_single_range(int rw, void __user *buf, size_t len, return 0; } EXPORT_SYMBOL(import_single_range); + +/** + * iov_iter_restore() - Restore a &struct iov_iter to the same state as when + * iov_iter_save_state() was called. + * + * @i: &struct iov_iter to restore + * @state: state to restore from + * + * Used after iov_iter_save_state() to bring restore @i, if operations may + * have advanced it. + * + * Note: only works on ITER_IOVEC, ITER_BVEC, and ITER_KVEC + */ +void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state) +{ + if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i)) && + !iov_iter_is_kvec(i)) + return; + i->iov_offset = state->iov_offset; + i->count = state->count; + /* + * For the *vec iters, nr_segs + iov is constant - if we increment + * the vec, then we also decrement the nr_segs count. Hence we don't + * need to track both of these, just one is enough and we can deduct + * the other from that. ITER_KVEC and ITER_IOVEC are the same struct + * size, so we can just increment the iov pointer as they are unionzed. + * ITER_BVEC _may_ be the same size on some archs, but on others it is + * not. Be safe and handle it separately. + */ + BUILD_BUG_ON(sizeof(struct iovec) != sizeof(struct kvec)); + if (iov_iter_is_bvec(i)) + i->bvec -= state->nr_segs - i->nr_segs; + else + i->iov -= state->nr_segs - i->nr_segs; + i->nr_segs = state->nr_segs; +} -- cgit v1.2.3 From cd65869512ab5668a5d16f789bc4da1319c435c4 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 10 Sep 2021 11:19:14 -0600 Subject: 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 @@ done: 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; } -- cgit v1.2.3 From 7dedd3e18077f996a10c47250ac85d080e5f474e Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 10 Sep 2021 11:19:58 -0600 Subject: Revert "iov_iter: track truncated size" This reverts commit 2112ff5ce0c1128fe7b4d19cfe7f2b8ce5b595fa. We no longer need to track the truncation count, the one user that did need it has been converted to using iov_iter_restore() instead. Signed-off-by: Jens Axboe --- include/linux/uio.h | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/include/linux/uio.h b/include/linux/uio.h index 984c4ab74859..207101a9c5c3 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -53,7 +53,6 @@ struct iov_iter { }; loff_t xarray_start; }; - size_t truncated; }; static inline enum iter_type iov_iter_type(const struct iov_iter *i) @@ -270,10 +269,8 @@ static inline void iov_iter_truncate(struct iov_iter *i, u64 count) * conversion in assignement is by definition greater than all * values of size_t, including old i->count. */ - if (i->count > count) { - i->truncated += i->count - count; + if (i->count > count) i->count = count; - } } /* @@ -282,7 +279,6 @@ static inline void iov_iter_truncate(struct iov_iter *i, u64 count) */ static inline void iov_iter_reexpand(struct iov_iter *i, size_t count) { - i->truncated -= count - i->count; i->count = count; } -- cgit v1.2.3 From b66ceaf324b394428bb47054140ddf03d8172e64 Mon Sep 17 00:00:00 2001 From: Pavel Begunkov Date: Wed, 15 Sep 2021 11:00:05 +0100 Subject: io_uring: move iopoll reissue into regular IO path 230d50d448acb ("io_uring: move reissue into regular IO path") made non-IOPOLL I/O to not retry from ki_complete handler. Follow it steps and do the same for IOPOLL. Same problems, same implementation, same -EAGAIN assumptions. Signed-off-by: Pavel Begunkov Link: https://lore.kernel.org/r/f80dfee2d5fa7678f0052a8ab3cfca9496a112ca.1631699928.git.asml.silence@gmail.com Signed-off-by: Jens Axboe --- fs/io_uring.c | 34 +++++++++++++++------------------- 1 file changed, 15 insertions(+), 19 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 25bda8a5a4e5..81b0c2723c72 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -736,7 +736,6 @@ enum { REQ_F_BUFFER_SELECTED_BIT, REQ_F_COMPLETE_INLINE_BIT, REQ_F_REISSUE_BIT, - REQ_F_DONT_REISSUE_BIT, REQ_F_CREDS_BIT, REQ_F_REFCOUNT_BIT, REQ_F_ARM_LTIMEOUT_BIT, @@ -783,8 +782,6 @@ enum { REQ_F_COMPLETE_INLINE = BIT(REQ_F_COMPLETE_INLINE_BIT), /* caller should reissue async */ REQ_F_REISSUE = BIT(REQ_F_REISSUE_BIT), - /* don't attempt request reissue, see io_rw_reissue() */ - REQ_F_DONT_REISSUE = BIT(REQ_F_DONT_REISSUE_BIT), /* supports async reads */ REQ_F_NOWAIT_READ = BIT(REQ_F_NOWAIT_READ_BIT), /* supports async writes */ @@ -2440,13 +2437,6 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events, req = list_first_entry(done, struct io_kiocb, inflight_entry); list_del(&req->inflight_entry); - if (READ_ONCE(req->result) == -EAGAIN && - !(req->flags & REQ_F_DONT_REISSUE)) { - req->iopoll_completed = 0; - io_req_task_queue_reissue(req); - continue; - } - __io_cqring_fill_event(ctx, req->user_data, req->result, io_put_rw_kbuf(req)); (*nr_events)++; @@ -2709,10 +2699,9 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2) if (kiocb->ki_flags & IOCB_WRITE) kiocb_end_write(req); if (unlikely(res != req->result)) { - if (!(res == -EAGAIN && io_rw_should_reissue(req) && - io_resubmit_prep(req))) { - req_set_fail(req); - req->flags |= REQ_F_DONT_REISSUE; + if (res == -EAGAIN && io_rw_should_reissue(req)) { + req->flags |= REQ_F_REISSUE; + return; } } @@ -2926,7 +2915,6 @@ static void kiocb_done(struct kiocb *kiocb, ssize_t ret, { struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb); struct io_async_rw *io = req->async_data; - bool check_reissue = kiocb->ki_complete == io_complete_rw; /* add previously done IO, if any */ if (io && io->bytes_done > 0) { @@ -2938,19 +2926,27 @@ static void kiocb_done(struct kiocb *kiocb, ssize_t ret, if (req->flags & REQ_F_CUR_POS) req->file->f_pos = kiocb->ki_pos; - if (ret >= 0 && check_reissue) + if (ret >= 0 && (kiocb->ki_complete == io_complete_rw)) __io_complete_rw(req, ret, 0, issue_flags); else io_rw_done(kiocb, ret); - if (check_reissue && (req->flags & REQ_F_REISSUE)) { + if (req->flags & REQ_F_REISSUE) { req->flags &= ~REQ_F_REISSUE; if (io_resubmit_prep(req)) { io_req_task_queue_reissue(req); } else { + unsigned int cflags = io_put_rw_kbuf(req); + struct io_ring_ctx *ctx = req->ctx; + req_set_fail(req); - __io_req_complete(req, issue_flags, ret, - io_put_rw_kbuf(req)); + if (issue_flags & IO_URING_F_NONBLOCK) { + mutex_lock(&ctx->uring_lock); + __io_req_complete(req, issue_flags, ret, cflags); + mutex_unlock(&ctx->uring_lock); + } else { + __io_req_complete(req, issue_flags, ret, cflags); + } } } } -- cgit v1.2.3