Re: [PATCH v3] iomap: Fix WARN_ON_ONCE() from unprivileged users

[Matthew Wilcox]

On Mon, Aug 31, 2020 at 01:25:34PM -0400, Qian Cai wrote:
> +	case IOMAP_DELALLOC:
> +		/*
> +		 * DIO is not serialised against mmap() access at all, and so
> +		 * if the page_mkwrite occurs between the writeback and the
> +		 * iomap_apply() call in the DIO path, then it will see the
> +		 * DELALLOC block that the page-mkwrite allocated.
> +		 */
> +		path = file_path(dio->iocb->ki_filp, pathname,
> +				 sizeof(pathname));
> +		if (IS_ERR(path))
> +			path = "(unknown)";
> +
> +		pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %s Comm: %.20s\n",
> +				    path, current->comm);

"File: %pD4"?