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

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Message-ID: <20200831180513.GC4080@lca.pw>
Date:   Mon, 31 Aug 2020 14:05:13 -0400
From:   Qian Cai <cai@....pw>
To:     Matthew Wilcox <willy@...radead.org>
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 06:42:19PM +0100, Matthew Wilcox wrote:
> 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"?

Sounds like a good idea. I could use that.