Re: [PATCH 04/18] fs/buffer.c: use accessor function to translate page index to sectors

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Mon, Sep 18, 2023 at 01:04:56PM +0200, Hannes Reinecke wrote:
> Use accessor functions block_index_to_sector() and block_sector_to_index()
> to translate the page index into the block sector and vice versa.

You missed two in grow_dev_page() (which I just happened upon):

        bh = folio_buffers(folio);
        if (bh) {
                if (bh->b_size == size) {
                        end_block = folio_init_buffers(folio, bdev,
                                        (sector_t)index << sizebits, size);
                        goto done;
                }
...
        spin_lock(&inode->i_mapping->private_lock);
        link_dev_buffers(folio, bh);
        end_block = folio_init_buffers(folio, bdev,
                        (sector_t)index << sizebits, size);

Can UBSAN be of help here?  It should catch shifting by a negative
amount.  That sizebits is calculated in grow_buffers:

        sizebits = PAGE_SHIFT - __ffs(size);