Re: [PATCH] bdev: add back PAGE_SIZE block size validation for sb_set_blocksize()

[Matthew Wilcox <willy@infradead.org>]

On Tue, Mar 04, 2025 at 05:53:01PM -0800, Luis Chamberlain wrote:
> The commit titled "block/bdev: lift block size restrictions to 64k"
> lifted the block layer's max supported block size to 64k inside the
> helper blk_validate_block_size() now that we support large folios.
> However in lifting the block size we also removed the silly use
> cases many filesystems have to use sb_set_blocksize() to *verify*
> that the block size < PAGE_SIZE. The call to sb_set_blocksize() can
> happen in-kernel given mkfs utilities *can* create for example an
> ext4 32k block size filesystem on x86_64, the issue we want to prevent
> is mounting it on x86_64 unless the filesystem supports LBS.
> 
> While, we could argue that such checks should be filesystem specific,
> there are much more users of sb_set_blocksize() than LBS enabled
> filesystem on linux-next, so just do the easier thing and bring back
> the PAGE_SIZE check for sb_set_blocksize() users.
> 
> This will ensure that tests such as generic/466 when run in a loop
> against say, ext4, won't try to try to actually mount a filesystem with
> a block size larger than your filesystem supports given your PAGE_SIZE
> and in the worst case crash.

So this is expedient because XFS happens to not call sb_set_blocksize()?
What is the path forward for filesystems which call sb_set_blocksize()
today and want to support LBS in future?