Re: [PATCH] xfs: fix sub-page uptodate handling

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Dec 04, 2019 at 06:28:04PM +0100, Christoph Hellwig wrote:
> bio complentions can race when a page spans more than one file system
> block.  Add a spinlock to synchronize marking the page uptodate.
> 
> Fixes: 9dc55f1389f9 ("iomap: add support for sub-pagesize buffered I/O without buffer heads")
> Reported-by: Jan Stancek <jstancek@redhat.com>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks good to me,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/iomap/buffered-io.c | 35 +++++++++++++++++++++++++----------
>  1 file changed, 25 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 512856a88106..340c15400423 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -28,6 +28,7 @@
>  struct iomap_page {
>  	atomic_t		read_count;
>  	atomic_t		write_count;
> +	spinlock_t		uptodate_lock;
>  	DECLARE_BITMAP(uptodate, PAGE_SIZE / 512);
>  };
>  
> @@ -51,6 +52,7 @@ iomap_page_create(struct inode *inode, struct page *page)
>  	iop = kmalloc(sizeof(*iop), GFP_NOFS | __GFP_NOFAIL);
>  	atomic_set(&iop->read_count, 0);
>  	atomic_set(&iop->write_count, 0);
> +	spin_lock_init(&iop->uptodate_lock);
>  	bitmap_zero(iop->uptodate, PAGE_SIZE / SECTOR_SIZE);
>  
>  	/*
> @@ -139,25 +141,38 @@ iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
>  }
>  
>  static void
> -iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
> +iomap_iop_set_range_uptodate(struct page *page, unsigned off, unsigned len)
>  {
>  	struct iomap_page *iop = to_iomap_page(page);
>  	struct inode *inode = page->mapping->host;
>  	unsigned first = off >> inode->i_blkbits;
>  	unsigned last = (off + len - 1) >> inode->i_blkbits;
> -	unsigned int i;
>  	bool uptodate = true;
> +	unsigned long flags;
> +	unsigned int i;
>  
> -	if (iop) {
> -		for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {
> -			if (i >= first && i <= last)
> -				set_bit(i, iop->uptodate);
> -			else if (!test_bit(i, iop->uptodate))
> -				uptodate = false;
> -		}
> +	spin_lock_irqsave(&iop->uptodate_lock, flags);
> +	for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {
> +		if (i >= first && i <= last)
> +			set_bit(i, iop->uptodate);
> +		else if (!test_bit(i, iop->uptodate))
> +			uptodate = false;
>  	}
>  
> -	if (uptodate && !PageError(page))
> +	if (uptodate)
> +		SetPageUptodate(page);
> +	spin_unlock_irqrestore(&iop->uptodate_lock, flags);
> +}
> +
> +static void
> +iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
> +{
> +	if (PageError(page))
> +		return;
> +
> +	if (page_has_private(page))
> +		iomap_iop_set_range_uptodate(page, off, len);
> +	else
>  		SetPageUptodate(page);
>  }
>  
> -- 
> 2.20.1
>