From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 17 Feb 2004 16:33:34 -0500 (EST) From: Rajesh Venkatasubramanian Subject: Re: [PATCH] mremap NULL pointer dereference fix In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds Cc: Andrew Morton , linux-kernel@vger.kernel.org, Linux-MM@kvack.org List-ID: > > > > This saves a goto. It works, but I wasn't able to trigger > > the oops without it either. > > To trigger the bug you have to have _just_ the right memory usage, I > suspect. You literally have to have the destination page directory > allocation unmap the _exact_ source page (which has to be clean) for the > bug to hit. A minor point. It is not necessary for the src to be clean because a parallel truncate can also invalidate the src. Actually, my test program uses truncate to invalidate the src. > Your version of the patch saves a goto in the source, but results in an > extra goto in the generated assembly unless the compiler is clever enough > to notice the double test for NULL. > > Never mind, that's a micro-optimization, and your version is cleaner. Yeah. Andrew's patch is lot cleaner than my _crap_ patch. > Let's go with it if Rajesh can verify that it fixes the problem for him. Yeap. Andrew's patch fixes the problem. I did put in a printk along with Andrew's patch to check whether the NULL src condition repeats. I could trigger the condition again, and the machine didn't oops because of the patch. Thanks, Rajesh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org