Commit 74cedf9b authored Nov 30, 2015 by Jan Kara Committed by Jens Axboe Nov 30, 2015

direct-io: Fix negative return from dio read beyond eof



Assume a filesystem with 4KB blocks. When a file has size 1000 bytes and
we issue direct IO read at offset 1024, blockdev_direct_IO() reads the
tail of the last block and the logic for handling short DIO reads in
dio_complete() results in a return value -24 (1000 - 1024) which
obviously confuses userspace.

Fix the problem by bailing out early once we sample i_size and can
reliably check that direct IO read starts beyond i_size.

Reported-by: Avi Kivity <avi@scylladb.com>
Fixes: 9fe55eea
CC: stable@vger.kernel.org
CC: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent bf4e6b4e

fs/direct-io.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -1169,6 +1169,15 @@ do_blockdev_direct_IO(struct kiocb iocb, struct inode inode,
		}
		}

		/* Once we sampled i_size check for reads beyond EOF */
		dio->i_size = i_size_read(inode);
		if (iov_iter_rw(iter) == READ && offset >= dio->i_size) {
		if (dio->flags & DIO_LOCKING)
		mutex_unlock(&inode->i_mutex);
		kmem_cache_free(dio_cache, dio);
		goto out;
		}

		/*
		* For file extending writes updating i_size before data writeouts
		* complete can expose uninitialized blocks in dumb filesystems.
		@@ -1222,7 +1231,6 @@ do_blockdev_direct_IO(struct kiocb iocb, struct inode inode,
		sdio.next_block_for_io = -1;

		dio->iocb = iocb;
		dio->i_size = i_size_read(inode);

		spin_lock_init(&dio->bio_lock);
		dio->refcount = 1;

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