Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754774AbZA3SPS (ORCPT ); Fri, 30 Jan 2009 13:15:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752708AbZA3SPE (ORCPT ); Fri, 30 Jan 2009 13:15:04 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:46660 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752255AbZA3SPC (ORCPT ); Fri, 30 Jan 2009 13:15:02 -0500 Date: Fri, 30 Jan 2009 10:14:26 -0800 (PST) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Hugh Dickins cc: Greg KH , Maksim Yevmenkin , Lee Schermerhorn , linux-kernel , Nick Piggin , Andrew Morton , will@crowder-design.com, Rik van Riel , KOSAKI Motohiro , KAMEZAWA Hiroyuki Subject: Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED file segments In-Reply-To: Message-ID: References: <1233259410.2315.75.camel@lts-notebook> <20090130055639.GA30950@suse.de> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2062 Lines: 61 On Fri, 30 Jan 2009, Hugh Dickins wrote: > > ... what I think you have done is break the vma merging on > ordinary files: because of that irritating VM_CAN_NONLINEAR > flag which generic_file_mmap() and some others add in. Ahh. Yes. VM_CAN_NONLINEAR is a "reverse flag", ie unlike the other flags it's to some degree about being extra _normal_, not about being odd. Most special flags tend to disable the VM from doing some clever thing, this one enables it. > To break the merging won't cause anyone much trouble, > but is a slight regression we should fix. Yeah. Just masking it off when comparing is probably the simplest option. Make it a separate #define just for readability. There might be other flags like this in the future. > I'd have been very upset not to find something ;) Yay for you ;) And yes, this is the kind of thing that probably does mean that we're better off with the no-semantic-changes patches in -stable. Linus --- mm/mmap.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index d3fa10a..c581df1 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -658,6 +658,9 @@ again: remove_next = 1 + (end > next->vm_end); validate_mm(mm); } +/* Flags that can be inherited from an existing mapping when merging */ +#define VM_MERGEABLE_FLAGS (VM_CAN_NONLINEAR) + /* * If the vma has a ->close operation then the driver probably needs to release * per-vma resources, so we don't attempt to merge those. @@ -665,7 +668,7 @@ again: remove_next = 1 + (end > next->vm_end); static inline int is_mergeable_vma(struct vm_area_struct *vma, struct file *file, unsigned long vm_flags) { - if (vma->vm_flags != vm_flags) + if ((vma->vm_flags ^ vm_flags) & ~VM_MERGEABLE_FLAGS) return 0; if (vma->vm_file != file) return 0; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/