Re: [PATCH 08/12] iomap: zeroing already holds invalidate_lock

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Sep 10, 2024 at 07:39:10AM +0300, Christoph Hellwig wrote:
> All callers of iomap_zero_range already hold invalidate_lock, so we can't
> take it again in iomap_file_buffered_write_punch_delalloc.
> 
> Use the passed in flags argument to detect if we're called from a zeroing
> operation and don't take the lock again in this case.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/iomap/buffered-io.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 52f285ae4bddcb..3d7e69a542518a 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1188,8 +1188,13 @@ static void iomap_write_delalloc_release(struct inode *inode, loff_t start_byte,
>  	 * folios and dirtying them via ->page_mkwrite whilst we walk the
>  	 * cache and perform delalloc extent removal. Failing to do this can
>  	 * leave dirty pages with no space reservation in the cache.
> +	 *
> +	 * For zeroing operations the callers already hold invalidate_lock.
>  	 */
> -	filemap_invalidate_lock(inode->i_mapping);
> +	if (flags & IOMAP_ZERO)
> +		rwsem_assert_held_write(&inode->i_mapping->invalidate_lock);

Does the other iomap_zero_range user (gfs2) take the invalidate lock?
AFAICT it doesn't.  Shouldn't we annotate iomap_zero_range to say that
callers have to hold i_rwsem and the invalidate_lock?

--D

> +	else
> +		filemap_invalidate_lock(inode->i_mapping);
>  	while (start_byte < scan_end_byte) {
>  		loff_t		data_end;
>  
> @@ -1240,7 +1245,8 @@ static void iomap_write_delalloc_release(struct inode *inode, loff_t start_byte,
>  		punch(inode, punch_start_byte, end_byte - punch_start_byte,
>  				iomap);
>  out_unlock:
> -	filemap_invalidate_unlock(inode->i_mapping);
> +	if (!(flags & IOMAP_ZERO))
> +		filemap_invalidate_unlock(inode->i_mapping);
>  }
>  
>  /*
> -- 
> 2.45.2
> 
>