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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7C42DC04A68 for ; Tue, 26 Jul 2022 19:11:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239759AbiGZTLA (ORCPT ); Tue, 26 Jul 2022 15:11:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44586 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239750AbiGZTK6 (ORCPT ); Tue, 26 Jul 2022 15:10:58 -0400 Received: from mail.efficios.com (mail.efficios.com [167.114.26.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D7A572C13E; Tue, 26 Jul 2022 12:10:56 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id A7BEA440A5A; Tue, 26 Jul 2022 15:10:55 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id Re7W2pLa6O7j; Tue, 26 Jul 2022 15:10:55 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 3F7044407F1; Tue, 26 Jul 2022 15:10:55 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 3F7044407F1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1658862655; bh=P0Jm8sAa/mrVBp/6VFgZCxx378vjOndqqAOWx+aDPbU=; h=Date:From:To:Message-ID:MIME-Version; b=a99k/XYmoPmrZXRbMD5KV4tR3u2lKCLrERtZX6p5K32C/QJhwMhdr9RGJg1aLj+dU W75olxaKy5Z0pmh1DaaZdJOP9wy4FO0d9OrhnpT0qZ+N8wkx/+FZi58hr4yOS6wbBH IIGlPSzibaHXH2deXlRpP3YcbYELcuZmV+EzBhWE7ijsAD88PT6QgpZrCG9sYwxWc5 hCrj7V7/Ohi8aVHdY+smwQ7uYouABVudlNFmer3VP/rPy8yndxWzVSX3dOgF6KTQm+ njzfwlOrTcdDn1d0Yx3DVI7IkRzVeJNoVDD9L+3h6e0YRTNsBwNOZNKE4c129BmHfH 3Wro93uZ9j69w== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id QxTQ8MLNlQw0; Tue, 26 Jul 2022 15:10:55 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id 2F0E8440D00; Tue, 26 Jul 2022 15:10:55 -0400 (EDT) Date: Tue, 26 Jul 2022 15:10:55 -0400 (EDT) From: Mathieu Desnoyers To: Peter Zijlstra Cc: linux-kernel , Thomas Gleixner , "Paul E . McKenney" , Boqun Feng , "H. Peter Anvin" , Paul Turner , linux-api , Peter Oskolkov Message-ID: <790910676.83207.1658862655138.JavaMail.zimbra@efficios.com> In-Reply-To: <20220622194617.1155957-1-mathieu.desnoyers@efficios.com> References: <20220622194617.1155957-1-mathieu.desnoyers@efficios.com> Subject: Re: [PATCH 1/2] rseq: Deprecate RSEQ_CS_FLAG_NO_RESTART_ON_* flags MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_4304 (ZimbraWebClient - FF100 (Linux)/8.8.15_GA_4304) Thread-Topic: rseq: Deprecate RSEQ_CS_FLAG_NO_RESTART_ON_* flags Thread-Index: okUY3mzxLKojq7TSqc3xEuNzQtQsig== Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Jun 22, 2022, at 3:46 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote: > The pretty much unused RSEQ_CS_FLAG_NO_RESTART_ON_* flags introduce > complexity in rseq, and are subtly buggy [1]. Solving those issues > requires introducing additional complexity in the rseq implementation > for each supported architecture. > > Considering that it complexifies the rseq ABI, I am proposing that we > deprecate those flags. [2] > > So far there appears to be consensus from maintainers of user-space > projects impacted by this feature that its removal would be a welcome > simplification. [3] > > The deprecation approach proposed here is to issue WARN_ON_ONCE() when > encountering those flags and kill the offending process with sigsegv. > This should allow us to quickly identify whether anyone yells at us for > removing this. Hi Peter, would you consider pulling this patch through the tip tree ? Thanks, Mathieu > > Link: > https://lore.kernel.org/lkml/20220618182515.95831-1-minhquangbui99@gmail.com/ > [1] > Link: > https://lore.kernel.org/lkml/258546133.12151.1655739550814.JavaMail.zimbra@efficios.com/ > [2] > Link: > https://lore.kernel.org/lkml/87pmj1enjh.fsf@email.froward.int.ebiederm.org/ [3] > Signed-off-by: Mathieu Desnoyers > --- > kernel/rseq.c | 23 ++++++++--------------- > 1 file changed, 8 insertions(+), 15 deletions(-) > > diff --git a/kernel/rseq.c b/kernel/rseq.c > index 97ac20b4f738..81d7dc80787b 100644 > --- a/kernel/rseq.c > +++ b/kernel/rseq.c > @@ -18,8 +18,9 @@ > #define CREATE_TRACE_POINTS > #include > > -#define RSEQ_CS_PREEMPT_MIGRATE_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE | \ > - RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT) > +#define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT | \ > + RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \ > + RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE) > > /* > * > @@ -175,23 +176,15 @@ static int rseq_need_restart(struct task_struct *t, u32 > cs_flags) > u32 flags, event_mask; > int ret; > > + if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS)) > + return -EINVAL; > + > /* Get thread flags. */ > ret = get_user(flags, &t->rseq->flags); > if (ret) > return ret; > > - /* Take critical section flags into account. */ > - flags |= cs_flags; > - > - /* > - * Restart on signal can only be inhibited when restart on > - * preempt and restart on migrate are inhibited too. Otherwise, > - * a preempted signal handler could fail to restart the prior > - * execution context on sigreturn. > - */ > - if (unlikely((flags & RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL) && > - (flags & RSEQ_CS_PREEMPT_MIGRATE_FLAGS) != > - RSEQ_CS_PREEMPT_MIGRATE_FLAGS)) > + if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS)) > return -EINVAL; > > /* > @@ -203,7 +196,7 @@ static int rseq_need_restart(struct task_struct *t, u32 > cs_flags) > t->rseq_event_mask = 0; > preempt_enable(); > > - return !!(event_mask & ~flags); > + return !!event_mask; > } > > static int clear_rseq_cs(struct task_struct *t) > -- > 2.30.2 -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com