Re: [PATCH 4/7] swapon(2): open swap with O_EXCL

[Al Viro <viro@zeniv.linux.org.uk>]

On Sun, Apr 28, 2024 at 12:46:23AM +0100, Al Viro wrote:

> Switching swap exclusion to O_EXCL could've been done back in 2003 or
> at any later point; it's just that swapon(2)/swapoff(2) is something that
> rarely gets a look...

BTW, a fun archaeological question: at which point has this
                /*
                 * Retrying may succeed; for example the folio may finish   
                 * writeback, or buffers may be cleaned.  This should not  
                 * happen very often; maybe we have old buffers attached to
                 * this blockdev's page cache and we're trying to change
                 * the block size?
                 */
                if (!try_to_free_buffers(folio)) {
                        end_block = ~0ULL;
                        goto unlock;
                }

in grow_dev_folio() (grow_dev_page() in earlier kernels) become unreachable?
I _think_ it was
commit fbc139f54fdb7edfec470421c2cc885d3796dfcd
Author: Linus Torvalds <torvalds@athlon.transmeta.com>
Date:   Mon Feb 4 20:19:55 2002 -0800

    v2.4.10.0.2 -> v2.4.10.0.3

      - more buffers-in-pagecache coherency

when set_blocksize() started to do
	sync_buffers(dev, 2);
	...
	invalidate_bdev(bdev, 1);
	truncate_inode_pages(bdev->bd_inode->i_mapping, 0);

at which point the "what if we'd found a page with attached buffers of the
wrong size?" should've become impossible.

Am I misreading that?