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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham 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 2472DC04AB4 for ; Fri, 17 May 2019 12:51:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ECCF22087B for ; Fri, 17 May 2019 12:51:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558097498; bh=pCPFO2CKYjVg71MaCPpDzfC5j8QTXByunWI5/YlRuLA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=weUCfr7qNUNI5SvReP4XTX9C/EfcTB+lSlGJwl6DHMsqhanIi2qHV76APz8+dqDFS WzKddlE35c3QHEtV10LAfMK906U41CiaBBJ1uwxLIk45kdznzg1EHVjxPA59SJds3l Z70BKfSDTbRjKsEFGOAICmxeBucyKLyUj6sMdL/Q= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728904AbfEQMvg (ORCPT ); Fri, 17 May 2019 08:51:36 -0400 Received: from mx2.suse.de ([195.135.220.15]:35714 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728100AbfEQMvg (ORCPT ); Fri, 17 May 2019 08:51:36 -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 5E16BAF59; Fri, 17 May 2019 12:51:35 +0000 (UTC) Date: Fri, 17 May 2019 14:51:34 +0200 From: Michal Hocko To: Konstantin Khlebnikov Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, Oleg Nesterov Subject: Re: [PATCH] mm: use down_read_killable for locking mmap_sem in access_remote_vm Message-ID: <20190517125134.GE1825@dhcp22.suse.cz> References: <155790847881.2798.7160461383704600177.stgit@buzz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <155790847881.2798.7160461383704600177.stgit@buzz> 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 Wed 15-05-19 11:21:18, Konstantin Khlebnikov wrote: > This function is used by ptrace and proc files like /proc/pid/cmdline and > /proc/pid/environ. Return 0 (bytes read) if current task is killed. Please add an explanation about why this is OK (as explained in the follow up email). > Mmap_sem could be locked for a long time or forever if something wrong. > > Signed-off-by: Konstantin Khlebnikov Acked-by: Michal Hocko > --- > mm/memory.c | 4 +++- > mm/nommu.c | 3 ++- > 2 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 96f1d473c89a..2e6846d09023 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4348,7 +4348,9 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm, > void *old_buf = buf; > int write = gup_flags & FOLL_WRITE; > > - down_read(&mm->mmap_sem); > + if (down_read_killable(&mm->mmap_sem)) > + return 0; > + > /* ignore errors, just check how much was successfully transferred */ > while (len) { > int bytes, ret, offset; > diff --git a/mm/nommu.c b/mm/nommu.c > index b492fd1fcf9f..cad8fb34088f 100644 > --- a/mm/nommu.c > +++ b/mm/nommu.c > @@ -1791,7 +1791,8 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm, > struct vm_area_struct *vma; > int write = gup_flags & FOLL_WRITE; > > - down_read(&mm->mmap_sem); > + if (down_read_killable(&mm->mmap_sem)) > + return 0; > > /* the access must start within one of the target process's mappings */ > vma = find_vma(mm, addr); -- Michal Hocko SUSE Labs