Re: [PATCH] iomap: Return zero in case of unsuccessful pagecache invalidation before DIO

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

On Thu, May 28, 2020 at 02:21:03PM -0500, Goldwyn Rodrigues wrote:
> 
> Filesystems such as btrfs are unable to guarantee page invalidation
> because pages could be locked as a part of the extent. Return zero

Locked for what?  filemap_write_and_wait_range should have just cleaned
them off.

> in case a page cache invalidation is unsuccessful so filesystems can
> fallback to buffered I/O. This is similar to
> generic_file_direct_write().
> 
> This takes care of the following invalidation warning during btrfs
> mixed buffered and direct I/O using iomap_dio_rw():
> 
> Page cache invalidation failure on direct I/O.  Possible data
> corruption due to collision with buffered I/O!
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index e4addfc58107..215315be6233 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -483,9 +483,15 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  	 */
>  	ret = invalidate_inode_pages2_range(mapping,
>  			pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
> -	if (ret)
> -		dio_warn_stale_pagecache(iocb->ki_filp);
> -	ret = 0;
> +	/*
> +	 * If a page can not be invalidated, return 0 to fall back
> +	 * to buffered write.
> +	 */
> +	if (ret) {
> +		if (ret == -EBUSY)
> +			ret = 0;
> +		goto out_free_dio;

XFS doesn't fall back to buffered io when directio fails, which means
this will cause a regression there.

Granted mixing write types is bogus...

--D

> +	}
>  
>  	if (iov_iter_rw(iter) == WRITE && !wait_for_completion &&
>  	    !inode->i_sb->s_dio_done_wq) {
> 
> -- 
> Goldwyn