linux-kernel - Re: [PATCH v3] iomap: Fix WARN_ON

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Message-ID: <20200831174219.GI14765@casper.infradead.org>
Date:   Mon, 31 Aug 2020 18:42:19 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Qian Cai <cai@....pw>
Cc:     darrick.wong@...cle.com, hch@...radead.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] iomap: Fix WARN_ON_ONCE() from unprivileged users

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"?