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

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Message-ID: <20240812163339.GD6043@frogsfrogsfrogs>
Date: Mon, 12 Aug 2024 09:33:39 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org, brauner@...nel.org,
	david@...morbit.com, jack@...e.cz, willy@...radead.org,
	yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v2 1/6] iomap: correct the range of a partial dirty clear

On Mon, Aug 12, 2024 at 08:11:54PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.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@...wei.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
> 
>