Commit 3e1f941d authored by Ilya Dryomov's avatar Ilya Dryomov Committed by Jens Axboe
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block: fix DIO handling regressions in blkdev_read_iter() 



Commit ceaa7625 ("block: move direct_IO into our own read_iter
handler") introduced several regressions for bdev DIO:

1. read spanning EOF always returns 0 instead of the number of bytes
   read.  This is because "count" is assigned early and isn't updated
   when the iterator is truncated:

     $ lsblk -o name,size /dev/vdb
     NAME SIZE
     vdb    1G
     $ xfs_io -d -c 'pread -b 4M 1021M 4M' /dev/vdb
     read 0/4194304 bytes at offset 1070596096
     0.000000 bytes, 0 ops; 0.0007 sec (0.000000 bytes/sec and 0.0000 ops/sec)

     instead of

     $ xfs_io -d -c 'pread -b 4M 1021M 4M' /dev/vdb
     read 3145728/4194304 bytes at offset 1070596096
     3 MiB, 1 ops; 0.0007 sec (3.865 GiB/sec and 1319.2612 ops/sec)

2. truncated iterator isn't reexpanded
3. iterator isn't reverted on blkdev_direct_IO() error
4. zero size read no longer skips atime update

Fixes: ceaa7625 ("block: move direct_IO into our own read_iter handler")
Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220201100420.25875-1-idryomov@gmail.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent b879f915

block/fops.c

+19 −14
Original line number Diff line number Diff line
@@ -566,34 +566,37 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to) 
{

	struct block_device *bdev = iocb->ki_filp->private_data;

	loff_t size = bdev_nr_bytes(bdev);

	size_t count = iov_iter_count(to);

	loff_t pos = iocb->ki_pos;

	size_t shorted = 0;

	ssize_t ret = 0;

	size_t count;



	if (unlikely(pos + count > size)) {

	if (unlikely(pos + iov_iter_count(to) > size)) {

		if (pos >= size)

			return 0;

		size -= pos;

		if (count > size) {

			shorted = count - size;

		shorted = iov_iter_count(to) - size;

		iov_iter_truncate(to, size);

	}

	}



	count = iov_iter_count(to);

	if (!count)

		goto reexpand; /* skip atime */



	if (iocb->ki_flags & IOCB_DIRECT) {

		struct address_space *mapping = iocb->ki_filp->f_mapping;



		if (iocb->ki_flags & IOCB_NOWAIT) {

			if (filemap_range_needs_writeback(mapping, iocb->ki_pos,

						iocb->ki_pos + count - 1))

				return -EAGAIN;

			if (filemap_range_needs_writeback(mapping, pos,

							  pos + count - 1)) {

				ret = -EAGAIN;

				goto reexpand;

			}

		} else {

			ret = filemap_write_and_wait_range(mapping,

						iocb->ki_pos,

					        iocb->ki_pos + count - 1);

			ret = filemap_write_and_wait_range(mapping, pos,

							   pos + count - 1);

			if (ret < 0)

				return ret;

				goto reexpand;

		}



		file_accessed(iocb->ki_filp);
@@ -603,12 +606,14 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to) 
			iocb->ki_pos += ret;

			count -= ret;

		}

		iov_iter_revert(to, count - iov_iter_count(to));

		if (ret < 0 || !count)

			return ret;

			goto reexpand;

	}



	ret = filemap_read(iocb, to, ret);



reexpand:

	if (unlikely(shorted))

		iov_iter_reexpand(to, iov_iter_count(to) + shorted);

	return ret;