From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753726AbbKXQM4 (ORCPT ); Tue, 24 Nov 2015 11:12:56 -0500 Received: from mail-lf0-f68.google.com ([209.85.215.68]:33094 "EHLO mail-lf0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753385AbbKXQMy (ORCPT ); Tue, 24 Nov 2015 11:12:54 -0500 Date: Tue, 24 Nov 2015 17:12:49 +0100 From: Piotr Kwapulinski To: Andrew Morton Cc: mhocko@suse.com, oleg@redhat.com, cmetcalf@ezchip.com, mszeredi@suse.cz, viro@zeniv.linux.org.uk, dave@stgolabs.net, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, iamjoonsoo.kim@lge.com, jack@suse.cz, xiexiuqi@huawei.com, vbabka@suse.cz, Vineet.Gupta1@synopsys.com, riel@redhat.com, gang.chen.5i5j@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v3] mm/mmap.c: remove incorrect MAP_FIXED flag comparison from mmap_region Message-ID: <20151124161248.GA1414@home.local> References: <20151123081946.GA21050@dhcp22.suse.cz> <1448300202-5004-1-git-send-email-kwapulinski.piotr@gmail.com> <20151123141401.0ad7e291be4d62ec83de7101@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151123141401.0ad7e291be4d62ec83de7101@linux-foundation.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 23, 2015 at 02:14:01PM -0800, Andrew Morton wrote: > On Mon, 23 Nov 2015 18:36:42 +0100 Piotr Kwapulinski wrote: > > > The following flag comparison in mmap_region makes no sense: > > > > if (!(vm_flags & MAP_FIXED)) > > return -ENOMEM; > > > > The condition is always false and thus the above "return -ENOMEM" is never > > executed. The vm_flags must not be compared with MAP_FIXED flag. > > The vm_flags may only be compared with VM_* flags. > > MAP_FIXED has the same value as VM_MAYREAD. > > Hitting the rlimit is a slow path and find_vma_intersection should realize > > that there is no overlapping VMA for !MAP_FIXED case pretty quickly. > > > > Remove the code that makes no sense. > > > > ... > > > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -1551,9 +1551,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr, > > * MAP_FIXED may remove pages of mappings that intersects with > > * requested mapping. Account for the pages it would unmap. > > */ > > - if (!(vm_flags & MAP_FIXED)) > > - return -ENOMEM; > > - > > nr_pages = count_vma_pages_range(mm, addr, addr + len); > > > > if (!may_expand_vm(mm, (len >> PAGE_SHIFT) - nr_pages)) > > Did you intend to retain the stale comment? It was my intention. This comment is still valid, even after removing the condition. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f50.google.com (mail-lf0-f50.google.com [209.85.215.50]) by kanga.kvack.org (Postfix) with ESMTP id 483576B0257 for ; Tue, 24 Nov 2015 11:12:55 -0500 (EST) Received: by lffu14 with SMTP id u14so27215909lff.1 for ; Tue, 24 Nov 2015 08:12:54 -0800 (PST) Received: from mail-lf0-x242.google.com (mail-lf0-x242.google.com. [2a00:1450:4010:c07::242]) by mx.google.com with ESMTPS id l80si13003482lfg.31.2015.11.24.08.12.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 24 Nov 2015 08:12:53 -0800 (PST) Received: by lfs39 with SMTP id 39so2398404lfs.3 for ; Tue, 24 Nov 2015 08:12:53 -0800 (PST) Date: Tue, 24 Nov 2015 17:12:49 +0100 From: Piotr Kwapulinski Subject: Re: [PATCH v3] mm/mmap.c: remove incorrect MAP_FIXED flag comparison from mmap_region Message-ID: <20151124161248.GA1414@home.local> References: <20151123081946.GA21050@dhcp22.suse.cz> <1448300202-5004-1-git-send-email-kwapulinski.piotr@gmail.com> <20151123141401.0ad7e291be4d62ec83de7101@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151123141401.0ad7e291be4d62ec83de7101@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: mhocko@suse.com, oleg@redhat.com, cmetcalf@ezchip.com, mszeredi@suse.cz, viro@zeniv.linux.org.uk, dave@stgolabs.net, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, iamjoonsoo.kim@lge.com, jack@suse.cz, xiexiuqi@huawei.com, vbabka@suse.cz, Vineet.Gupta1@synopsys.com, riel@redhat.com, gang.chen.5i5j@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org On Mon, Nov 23, 2015 at 02:14:01PM -0800, Andrew Morton wrote: > On Mon, 23 Nov 2015 18:36:42 +0100 Piotr Kwapulinski wrote: > > > The following flag comparison in mmap_region makes no sense: > > > > if (!(vm_flags & MAP_FIXED)) > > return -ENOMEM; > > > > The condition is always false and thus the above "return -ENOMEM" is never > > executed. The vm_flags must not be compared with MAP_FIXED flag. > > The vm_flags may only be compared with VM_* flags. > > MAP_FIXED has the same value as VM_MAYREAD. > > Hitting the rlimit is a slow path and find_vma_intersection should realize > > that there is no overlapping VMA for !MAP_FIXED case pretty quickly. > > > > Remove the code that makes no sense. > > > > ... > > > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -1551,9 +1551,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr, > > * MAP_FIXED may remove pages of mappings that intersects with > > * requested mapping. Account for the pages it would unmap. > > */ > > - if (!(vm_flags & MAP_FIXED)) > > - return -ENOMEM; > > - > > nr_pages = count_vma_pages_range(mm, addr, addr + len); > > > > if (!may_expand_vm(mm, (len >> PAGE_SHIFT) - nr_pages)) > > Did you intend to retain the stale comment? It was my intention. This comment is still valid, even after removing the condition. -- 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: email@kvack.org