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Commit 6a43074e authored by Jens Axboe's avatar Jens Axboe
Browse files

block: properly handle IOCB_NOWAIT for async O_DIRECT IO 



A caller is supposed to pass in REQ_NOWAIT if we can't block for any
given operation, but O_DIRECT for block devices just ignore this. Hence
we'll block for various resource shortages on the block layer side,
like having to wait for requests.

Use the new REQ_NOWAIT_INLINE to ask for this error to be returned
inline, so we can handle it appropriately and return -EAGAIN to the
caller.

Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 893a1c97

fs/block_dev.c

+50 −8
Original line number Diff line number Diff line
@@ -344,15 +344,24 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages) 
	struct bio *bio;

	bool is_poll = (iocb->ki_flags & IOCB_HIPRI) != 0;

	bool is_read = (iov_iter_rw(iter) == READ), is_sync;

	bool nowait = (iocb->ki_flags & IOCB_NOWAIT) != 0;

	loff_t pos = iocb->ki_pos;

	blk_qc_t qc = BLK_QC_T_NONE;

	int ret = 0;

	gfp_t gfp;

	ssize_t ret;



	if ((pos | iov_iter_alignment(iter)) &

	    (bdev_logical_block_size(bdev) - 1))

		return -EINVAL;



	bio = bio_alloc_bioset(GFP_KERNEL, nr_pages, &blkdev_dio_pool);

	if (nowait)

		gfp = GFP_NOWAIT;

	else

		gfp = GFP_KERNEL;



	bio = bio_alloc_bioset(gfp, nr_pages, &blkdev_dio_pool);

	if (!bio)

		return -EAGAIN;



	dio = container_of(bio, struct blkdev_dio, bio);

	dio->is_sync = is_sync = is_sync_kiocb(iocb);
@@ -374,7 +383,10 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages) 
	if (!is_poll)

		blk_start_plug(&plug);



	ret = 0;

	for (;;) {

		int err;



		bio_set_dev(bio, bdev);

		bio->bi_iter.bi_sector = pos >> 9;

		bio->bi_write_hint = iocb->ki_hint;
@@ -382,8 +394,10 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages) 
		bio->bi_end_io = blkdev_bio_end_io;

		bio->bi_ioprio = iocb->ki_ioprio;



		ret = bio_iov_iter_get_pages(bio, iter);

		if (unlikely(ret)) {

		err = bio_iov_iter_get_pages(bio, iter);

		if (unlikely(err)) {

			if (!ret)

				ret = err;

			bio->bi_status = BLK_STS_IOERR;

			bio_endio(bio);

			break;
@@ -398,6 +412,14 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages) 
			task_io_account_write(bio->bi_iter.bi_size);

		}



		/*

		 * Tell underlying layer to not block for resource shortage.

		 * And if we would have blocked, return error inline instead

		 * of through the bio->bi_end_io() callback.

		 */

		if (nowait)

			bio->bi_opf |= (REQ_NOWAIT | REQ_NOWAIT_INLINE);



		dio->size += bio->bi_iter.bi_size;

		pos += bio->bi_iter.bi_size;
@@ -411,6 +433,11 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages) 
			}



			qc = submit_bio(bio);

			if (qc == BLK_QC_T_EAGAIN) {

				if (!ret)

					ret = -EAGAIN;

				goto error;

			}



			if (polled)

				WRITE_ONCE(iocb->ki_cookie, qc);
@@ -431,8 +458,20 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages) 
			atomic_inc(&dio->ref);

		}



		submit_bio(bio);

		bio = bio_alloc(GFP_KERNEL, nr_pages);

		qc = submit_bio(bio);

		if (qc == BLK_QC_T_EAGAIN) {

			if (!ret)

				ret = -EAGAIN;

			goto error;

		}

		ret += bio->bi_iter.bi_size;



		bio = bio_alloc(gfp, nr_pages);

		if (!bio) {

			if (!ret)

				ret = -EAGAIN;

			goto error;

		}

	}



	if (!is_poll)
@@ -452,13 +491,16 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages) 
	}

	__set_current_state(TASK_RUNNING);



out:

	if (!ret)

		ret = blk_status_to_errno(dio->bio.bi_status);

	if (likely(!ret))

		ret = dio->size;



	bio_put(&dio->bio);

	return ret;

error:

	if (!is_poll)

		blk_finish_plug(&plug);

	goto out;

}



static ssize_t