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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,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 2CA04C6778F for ; Thu, 26 Jul 2018 13:20:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D78B42083F for ; Thu, 26 Jul 2018 13:20:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D78B42083F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730728AbeGZOho (ORCPT ); Thu, 26 Jul 2018 10:37:44 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:49012 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729410AbeGZOho (ORCPT ); Thu, 26 Jul 2018 10:37:44 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id F1043879C4; Thu, 26 Jul 2018 13:20:52 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id 6F6FD1C5B0; Thu, 26 Jul 2018 13:20:51 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 26 Jul 2018 15:20:52 +0200 (CEST) Date: Thu, 26 Jul 2018 15:20:50 +0200 From: Oleg Nesterov To: "Eric W. Biederman" Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, Wen Yang , majiang Subject: Re: [PATCH 18/20] signal: Add calculate_sigpending() Message-ID: <20180726132050.GA32718@redhat.com> References: <87efft5ncd.fsf_-_@xmission.com> <20180724032419.20231-18-ebiederm@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180724032419.20231-18-ebiederm@xmission.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Thu, 26 Jul 2018 13:20:53 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Thu, 26 Jul 2018 13:20:53 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'oleg@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/23, Eric W. Biederman wrote: > > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1988,6 +1988,7 @@ static __latent_entropy struct task_struct *copy_process( > &p->signal->thread_head); > } > attach_pid(p, PIDTYPE_PID); > + calculate_sigpending(p); In theory this looks racy if !CLONE_SIGHAND, please see below > +void calculate_sigpending(struct task_struct *new) > +{ > + /* Have any signals or users of TIF_SIGPENDING been delayed > + * until after fork? > + */ > + bool pending = (new->jobctl & JOBCTL_PENDING_MASK) || > + PENDING(&new->pending, &new->blocked) || > + PENDING(&new->signal->shared_pending, &new->blocked) || > + freezing(new) || klp_patch_pending(new); note that we do not hold new->sighand->siglock, but this "new" task is already visible to find_task_by_vpid/etc; so a new signal can come right after this check, > + update_tsk_thread_flag(new, TIF_SIGPENDING, pending); and then update_tsk_thread_flag() can wrongly clear TIF_SIGPENDING. Easy to fix, but perhaps we can simply add recalc_sigpending() into schedule_tail() ? It already does more than just finish_task_switch/etc. This way we do not need the new helper (which btw can only be used by copy_process). Note also that either way you can remove set_tsk_thread_flag(TIF_SIGPENDING) from ptrace_init_task(). Oleg.