Re: [PATCH 01/67] mm: Stop filemap_read() from grabbing a superfluous page

Matthew Wilcox
2021-10-19T18:30:02Z

On Mon, Oct 18, 2021 at 03:50:32PM +0100, David Howells wrote:
> @@ -2625,6 +2625,10 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
> if ((iocb->ki_flags & IOCB_WAITQ) && already_read)
> iocb->ki_flags |= IOCB_NOWAIT;
>
> + isize = i_size_read(inode);
> + if (unlikely(iocb->ki_pos >= isize))
> + goto put_pages;
> +

Is there a good reason to assign to isize here? I'd rather not,
because it complicates analysis, and a later change might look at
the isize read here, not realising it was a racy use. So I'd
rather see:

if (unlikely(iocb->ki_pos >= i_size_read(inode)))
goto put_pages;