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Instead we can rely on page unlocking callbacks to support retry based async IO. This is a lot more efficient than doing async thread offload. The retry is done similarly to how we handle poll based retry. From the unlock callback, we simply queue the retry to a task_work based handler. Signed-off-by: Jens Axboe --- fs/io_uring.c | 101 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 101 insertions(+) diff --git a/fs/io_uring.c b/fs/io_uring.c index e95481c552ff..f0ca98bb688f 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -498,6 +498,8 @@ struct io_async_rw { struct iovec *iov; ssize_t nr_segs; ssize_t size; + struct wait_page_async wait; + struct callback_head task_work; }; struct io_async_ctx { @@ -2568,6 +2570,101 @@ static int io_read_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe, return 0; } +static void io_async_buf_cancel(struct callback_head *cb) +{ + struct io_async_rw *rw; + struct io_ring_ctx *ctx; + struct io_kiocb *req; + + rw = container_of(cb, struct io_async_rw, task_work); + req = rw->wait.wait.private; + ctx = req->ctx; + + spin_lock_irq(&ctx->completion_lock); + io_cqring_fill_event(req, -ECANCELED); + io_commit_cqring(ctx); + spin_unlock_irq(&ctx->completion_lock); + + io_cqring_ev_posted(ctx); + req_set_fail_links(req); + io_double_put_req(req); +} + +static void io_async_buf_retry(struct callback_head *cb) +{ + struct io_async_rw *rw; + struct io_ring_ctx *ctx; + struct io_kiocb *req; + + rw = container_of(cb, struct io_async_rw, task_work); + req = rw->wait.wait.private; + ctx = req->ctx; + + __set_current_state(TASK_RUNNING); + mutex_lock(&ctx->uring_lock); + __io_queue_sqe(req, NULL); + mutex_unlock(&ctx->uring_lock); +} + +static int io_async_buf_func(struct wait_queue_entry *wait, unsigned mode, + int sync, void *arg) +{ + struct wait_page_async *wp; + struct io_kiocb *req = wait->private; + struct io_async_rw *rw = &req->io->rw; + struct wait_page_key *key = arg; + struct task_struct *tsk; + int ret; + + wp = container_of(wait, struct wait_page_async, wait); + if (wp->key.page != key->page) + return 0; + if (wp->key.bit_nr != key->bit_nr) + return 0; + if (test_bit(PG_locked, &key->page->flags)) + return -1; + + list_del_init(&wait->entry); + + init_task_work(&rw->task_work, io_async_buf_retry); + /* submit ref gets dropped, acquire a new one */ + refcount_inc(&req->refs); + tsk = req->task; + ret = task_work_add(tsk, &rw->task_work, true); + if (unlikely(ret)) { + /* queue just for cancelation */ + init_task_work(&rw->task_work, io_async_buf_cancel); + tsk = io_wq_get_task(req->ctx->io_wq); + task_work_add(tsk, &rw->task_work, true); + } + wake_up_process(tsk); + return 1; +} + +static bool io_rw_should_retry(struct io_kiocb *req) +{ + struct kiocb *kiocb = &req->rw.kiocb; + int ret; + + /* already tried, or we're doing O_DIRECT */ + if (kiocb->ki_flags & (IOCB_DIRECT | IOCB_WAITQ)) + return false; + /* + * just use poll if we can, and don't attempt if the fs doesn't + * support callback based unlocks + */ + if (file_can_poll(req->file) || !(req->file->f_mode & FMODE_BUF_RASYNC)) + return false; + + ret = kiocb_wait_page_async_init(kiocb, &req->io->rw.wait, + io_async_buf_func, req); + if (ret) + return false; + get_task_struct(current); + req->task = current; + return true; +} + static int io_read(struct io_kiocb *req, bool force_nonblock) { struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs; @@ -2601,6 +2698,7 @@ static int io_read(struct io_kiocb *req, bool force_nonblock) if (!ret) { ssize_t ret2; +retry: if (req->file->f_op->read_iter) ret2 = call_read_iter(req->file, kiocb, &iter); else @@ -2619,6 +2717,9 @@ static int io_read(struct io_kiocb *req, bool force_nonblock) if (!(req->flags & REQ_F_NOWAIT) && !file_can_poll(req->file)) req->flags |= REQ_F_MUST_PUNT; + if (io_rw_should_retry(req)) + goto retry; + kiocb->ki_flags &= ~IOCB_WAITQ; return -EAGAIN; } }