From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, T_DKIMWL_WL_HIGH,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 08A93C04AAD for ; Tue, 7 May 2019 17:42:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D1412214C6 for ; Tue, 7 May 2019 17:42:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1557250940; bh=IB53AUA4paDM5FMFWmLdu6yxUS3R+QMnsp6P8aQgDrw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=DNoXPq/Ch18zBk9brh1USGvFQhuRpeZYya0WEu4NVqbWJJqUtJeEFJHKx7gsOZXBQ WAk+0Tart7acoJkYiVXhHSMw0ldYCnWtOe9RhM5gAxOxMK8lR60TphSVVln0pg3Ne+ oeeyk4tb6737ZEbdnoTzf2VlNUbBtbH+RthxAkl4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727495AbfEGRmT (ORCPT ); Tue, 7 May 2019 13:42:19 -0400 Received: from mx2.suse.de ([195.135.220.15]:57720 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726607AbfEGRmT (ORCPT ); Tue, 7 May 2019 13:42:19 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 14066AF7C; Tue, 7 May 2019 17:42:17 +0000 (UTC) Date: Tue, 7 May 2019 19:42:15 +0200 From: Michal Hocko To: Michal =?iso-8859-1?Q?Koutn=FD?= Cc: gorcunov@gmail.com, akpm@linux-foundation.org, arunks@codeaurora.org, brgl@bgdev.pl, geert+renesas@glider.be, ldufour@linux.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mguzik@redhat.com, rppt@linux.ibm.com, vbabka@suse.cz, ktkhai@virtuozzo.com Subject: Re: [PATCH v3 2/2] prctl_set_mm: downgrade mmap_sem to read lock Message-ID: <20190507174215.GT31017@dhcp22.suse.cz> References: <0a48e0a2-a282-159e-a56e-201fbc0faa91@virtuozzo.com> <20190502125203.24014-1-mkoutny@suse.com> <20190502125203.24014-3-mkoutny@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190502125203.24014-3-mkoutny@suse.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 02-05-19 14:52:03, Michal Koutny wrote: > The commit a3b609ef9f8b ("proc read mm's {arg,env}_{start,end} with mmap > semaphore taken.") added synchronization of reading argument/environment > boundaries under mmap_sem. Later commit 88aa7cc688d4 ("mm: introduce > arg_lock to protect arg_start|end and env_start|end in mm_struct") > avoided the coarse use of mmap_sem in similar situations. But there > still remained two places that (mis)use mmap_sem. > > get_cmdline should also use arg_lock instead of mmap_sem when it reads the > boundaries. > > The second place that should use arg_lock is in prctl_set_mm. By > protecting the boundaries fields with the arg_lock, we can downgrade > mmap_sem to reader lock (analogous to what we already do in > prctl_set_mm_map). > > v2: call find_vma without arg_lock held > v3: squashed get_cmdline arg_lock patch > > Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct") > Cc: Yang Shi > Cc: Mateusz Guzik > CC: Cyrill Gorcunov > Co-developed-by: Laurent Dufour > Signed-off-by: Laurent Dufour > Signed-off-by: Michal Koutný Just a nit. S-o-b chain is not correct here. The first s-o-b should match the author (From) of the patch. Acked-by: Michal Hocko > --- > kernel/sys.c | 10 ++++++++-- > mm/util.c | 4 ++-- > 2 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/kernel/sys.c b/kernel/sys.c > index 5e0a5edf47f8..14be57840511 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2122,9 +2122,14 @@ static int prctl_set_mm(int opt, unsigned long addr, > > error = -EINVAL; > > - down_write(&mm->mmap_sem); > + /* > + * arg_lock protects concurent updates of arg boundaries, we need mmap_sem for > + * a) concurrent sys_brk, b) finding VMA for addr validation. > + */ > + down_read(&mm->mmap_sem); > vma = find_vma(mm, addr); > > + spin_lock(&mm->arg_lock); > prctl_map.start_code = mm->start_code; > prctl_map.end_code = mm->end_code; > prctl_map.start_data = mm->start_data; > @@ -2212,7 +2217,8 @@ static int prctl_set_mm(int opt, unsigned long addr, > > error = 0; > out: > - up_write(&mm->mmap_sem); > + spin_unlock(&mm->arg_lock); > + up_read(&mm->mmap_sem); > return error; > } > > diff --git a/mm/util.c b/mm/util.c > index 43a2984bccaa..5cf0e84a0823 100644 > --- a/mm/util.c > +++ b/mm/util.c > @@ -758,12 +758,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen) > if (!mm->arg_end) > goto out_mm; /* Shh! No looking before we're done */ > > - down_read(&mm->mmap_sem); > + spin_lock(&mm->arg_lock); > arg_start = mm->arg_start; > arg_end = mm->arg_end; > env_start = mm->env_start; > env_end = mm->env_end; > - up_read(&mm->mmap_sem); > + spin_unlock(&mm->arg_lock); > > len = arg_end - arg_start; > > -- > 2.16.4 -- Michal Hocko SUSE Labs