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block: fix DIO handling regressions in blkdev_read_iter()

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Commit ceaa762527 ("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: ceaa762527 ("block: move direct_IO into our own read_iter handler")
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220201100420.25875-1-idryomov@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ilya Dryomov 2022-02-01 11:04:20 +01:00 committed by Jens Axboe
parent b879f915bc
commit 3e1f941dd9
1 changed files with 19 additions and 14 deletions
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33
block/fops.c
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@ -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;
iov_iter_truncate(to, 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;