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

[Zhang Yi]

On 2024/8/13 0:33, Darrick J. Wong wrote:
> On Mon, Aug 12, 2024 at 08:11:54PM +0800, Zhang Yi wrote:
>> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
>>
>> 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@xxxxxxxxxx>
>> ---
>>  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?
> 

Sorry, I don't find a common macro now, if we want to avoid integer division,
how about open code here?

	first_blk = round_up(off, i_blocksize(inode)) >> inode->i_blkbits;

Thanks,
Yi.

> 
>> +	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
>>
>>