From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 22 Dec 2006 12:17:06 +1100 From: David Gibson To: Segher Boessenkool Subject: Re: [powerpc] Fix bogus BUG_ON() in in hugetlb_get_unmapped_area() Message-ID: <20061222011706.GA27396@localhost.localdomain> References: <20061221222303.GA6418@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Cc: Andrew Morton , libhugetlbfs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, William Lee Irwin , linuxppc-dev@ozlabs.org, Paul Mackerras List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, Dec 22, 2006 at 01:31:26AM +0100, Segher Boessenkool wrote: > > + if (len > TASK_SIZE) > > + return -ENOMEM; > > Shouldn't that be addr+len instead? The check looks incomplete > otherwise. And you meant ">=" I guess? No. Have a look at the other hugetlb_get_unmapped_area() implementations. Because this is in the get_unmapped_area() path, 'addr' is just a hint, so checking addr+len would give bogus failures. This test is, I believe, essentially an optimization - if it fails, we're never going to find a suitable addr, so we might as well give up now. > > - /* Paranoia, caller should have dealt with this */ > > - BUG_ON((addr + len) > 0x100000000UL); > > - > > Any real reason to remove the paranoia check? If it's trivially > always satisfied, the compiler will get rid of it for you :-) Yes - this is the very bug on which was causing crashes - the "caller should have dealt with this" comment is wrong. The test has been moved into htlb_check_hinted_area() and now simply fails (and so falls back to searching for a suitable address), rather than BUG()ing. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson