Re: [PATCH v2 1/6] iomap: correct the range of a partial dirty clear

Darrick J. Wong
2024-08-12T16:33:40Z

On Mon, Aug 12, 2024 at 08:11:54PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@huawei.com>
>
> The block range calculation in ifs_clear_range_dirty() is incorrect when
> partial clear a range in a folio. We can't clear the dirty bit of the
> first block or the last block if the start or end offset is blocksize
> unaligned, this has not yet caused any issue since we always clear a
> whole folio in iomap_writepage_map()->iomap_clear_range_dirty(). Fix
> this by round up the first block and round down the last block and
> correct the calculation of nr_blks.
>
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
> ---
> fs/iomap/buffered-io.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index f420c53d86ac..4da453394aaf 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -138,11 +138,14 @@ static void ifs_clear_range_dirty(struct folio *folio,
> {
> struct inode *inode = folio->mapping->host;
> unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
> - unsigned int first_blk = (off >> inode->i_blkbits);
> - unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
> - unsigned int nr_blks = last_blk - first_blk + 1;
> + unsigned int first_blk = DIV_ROUND_UP(off, i_blocksize(inode));

Is there a round up macro that doesn't involve integer division?

--D

> + unsigned int last_blk = (off + len) >> inode->i_blkbits;
> + unsigned int nr_blks = last_blk - first_blk;
> unsigned long flags;
>
> + if (!nr_blks)
> + return;
> +
> spin_lock_irqsave(&ifs->state_lock, flags);
> bitmap_clear(ifs->state, first_blk + blks_per_folio, nr_blks);
> spin_unlock_irqrestore(&ifs->state_lock, flags);
> --
> 2.39.2
>
>