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Date: Fri, 20 Oct 2023 20:37:26 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Hannes Reinecke <hare@suse.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>, Christoph Hellwig <hch@lst.de>,
	Jens Axboe <axboe@kernel.dk>, Pankaj Raghav <p.raghav@samsung.com>,
	linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 04/18] fs/buffer.c: use accessor function to translate
 page index to sectors
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References: <20230918110510.66470-1-hare@suse.de>
 <20230918110510.66470-5-hare@suse.de>
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In-Reply-To: <20230918110510.66470-5-hare@suse.de>

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);