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 4C7BFC433EF for ; Thu, 28 Apr 2022 10:14:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240116AbiD1KR2 (ORCPT ); Thu, 28 Apr 2022 06:17:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35476 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238568AbiD1KQu (ORCPT ); Thu, 28 Apr 2022 06:16:50 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 067A533898; Thu, 28 Apr 2022 03:08:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=0hAD2TvAOIWLHlJzzIV1W5Ntb/AneBoQ7gA0EhNRMB4=; b=Yd4l882RZ59I/9Pp2tdng5bTdm 9V8Vgio3Lp0j1G7ughnktXJFE91D5GHMBUq6ALxMgdRL9ZJmU4Abwp3tvGFGKaXgOatfXZKb/oQdD x3wiZ1rDf7PZBL6Onj7DkhqOHeCTYN1lX5P7AbwfTBySWC/8LrYFqNnvMZFncuxJ5yoBMOlgCbjAK EJ4XAQ0xF/4hvOAU9OZmiEMqt1YwLvYB9s1eE3AsuCNoyVBnie16J9czUCUpgrtf/Rz049giD49BM DrqbF6I+/Y9rUJpxscic27P0yHmEC+DqiQsP5qWYw2oSdEPE3HXIAgndMJf9YOeVL6tx+sk3dHTKG MWc/s6qg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nk13j-00BP3P-DL; Thu, 28 Apr 2022 10:07:39 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id D59BB3001AD; Thu, 28 Apr 2022 12:07:36 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BB55D2029F872; Thu, 28 Apr 2022 12:07:36 +0200 (CEST) Date: Thu, 28 Apr 2022 12:07:36 +0200 From: Peter Zijlstra To: "Eric W. Biederman" Cc: linux-kernel@vger.kernel.org, rjw@rjwysocki.net, oleg@redhat.com, mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de, Will Deacon , tj@kernel.org, linux-pm@vger.kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Jann Horn , Kees Cook Subject: Re: [PATCH 0/9] ptrace: cleaning up ptrace_stop Message-ID: References: <20220421150248.667412396@infradead.org> <20220421150654.817117821@infradead.org> <87czhap9dy.fsf@email.froward.int.ebiederm.org> <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On Tue, Apr 26, 2022 at 05:50:21PM -0500, Eric W. Biederman wrote: > .... Peter Zijlstra has > been rewriting the classic freezer and in earlier parts of this > discussion so I presume it is also a problem for PREEMPT_RT. Ah, the freezer thing is in fact a sched/arm64 issue, the common issue between these two issues is ptrace though. Specifically, on recent arm64 chips only a subset of CPUs can execute arm32 code and 32bit processes are restricted to that subset. If by some mishap you try and execute a 32bit task on a non-capable CPU it gets terminated without prejudice. Now, the current freezer has this problem that tasks can spuriously thaw too soon (where too soon is before SMP is restored) which leads to these 32bit tasks being killed dead. That, and it was a good excuse to fix up the current freezer :-)