Commit c8d317aa authored Sep 29, 2020 by Hao Xu Committed by Jens Axboe Sep 29, 2020

io_uring: fix async buffered reads when readahead is disabled



The async buffered reads feature is not working when readahead is
turned off. There are two things to concern:

- when doing retry in io_read, not only the IOCB_WAITQ flag but also
  the IOCB_NOWAIT flag is still set, which makes it goes to would_block
  phase in generic_file_buffered_read() and then return -EAGAIN. After
  that, the io-wq thread work is queued, and later doing the async
  reads in the old way.

- even if we remove IOCB_NOWAIT when doing retry, the feature is still
  not running properly, since in generic_file_buffered_read() it goes to
  lock_page_killable() after calling mapping->a_ops->readpage() to do
  IO, and thus causing process to sleep.

Fixes: 1a0a7853 ("mm: support async buffered reads in generic_file_buffered_read()")
Fixes: 3b2a4439 ("io_uring: get rid of kiocb_wait_page_queue_init()")
Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent fad8e0de

fs/io_uring.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -3049,6 +3049,7 @@ static int io_async_buf_func(struct wait_queue_entry *wait, unsigned mode,
		if (!wake_page_match(wpq, key))
		return 0;

		req->rw.kiocb.ki_flags &= ~IOCB_WAITQ;
		list_del_init(&wait->entry);

		init_task_work(&req->task_work, io_req_task_submit);
		@@ -3106,6 +3107,7 @@ static bool io_rw_should_retry(struct io_kiocb *req)
		wait->wait.flags = 0;
		INIT_LIST_HEAD(&wait->wait.entry);
		kiocb->ki_flags \|= IOCB_WAITQ;
		kiocb->ki_flags &= ~IOCB_NOWAIT;
		kiocb->ki_waitq = wait;

		io_get_req_task(req);

mm/filemap.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -2267,7 +2267,11 @@ readpage:
		}

		if (!PageUptodate(page)) {
		if (iocb->ki_flags & IOCB_WAITQ)
		error = lock_page_async(page, iocb->ki_waitq);
		else
		error = lock_page_killable(page);

		if (unlikely(error))
		goto readpage_error;
		if (!PageUptodate(page)) {

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