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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 09BE7C433E0 for ; Mon, 20 Jul 2020 08:41:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D21FA2176B for ; Mon, 20 Jul 2020 08:41:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Fr2uojTE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728014AbgGTIlW (ORCPT ); Mon, 20 Jul 2020 04:41:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58232 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726030AbgGTIlV (ORCPT ); Mon, 20 Jul 2020 04:41:21 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B1FE4C061794 for ; Mon, 20 Jul 2020 01:41:21 -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=Q7H8FhLFAWwenVaWoaULPDjpconR6IkD92nyts4yKVU=; b=Fr2uojTEhUZfwR7jKyuXuTVajc xK+lrm8l8kqREEwn+X9PxXcQqNfWBt+B3cYfNZzqrOvM9ILI7FSw+r9nIu7WwRr9vybDpj/ZXDxKr ywRW95Iac4x7Anzm8BGj0D8lRWb+gSw7M2Z/apnwlTp91JbjxGrOlLD/h7TphzFfRWV8N9dy0F0oE rvAk/hzgrwQ2c/m31mUIjLlM2bszkbcBTN8Qg8tMGjaL5520sl8hTmOcHpMcMbnRpSdVgMuQEo3yc +t9gGZjqo4CyrSjyhkgGoX281Ux3rRT/1Ee8gMyNEdFeGxxQZLn84/W2ogzeSZv0cUhjIT/1VJ8sA p8uOmw+Q==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jxRMF-0007Kv-5p; Mon, 20 Jul 2020 08:41:11 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 782453010C8; Mon, 20 Jul 2020 10:41:06 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 444732129EDD8; Mon, 20 Jul 2020 10:41:06 +0200 (CEST) Date: Mon, 20 Jul 2020 10:41:06 +0200 From: Peter Zijlstra To: Oleg Nesterov Cc: Jiri Slaby , Christian Brauner , christian@brauner.io, "Eric W. Biederman" , Linux kernel mailing list , Mel Gorman , Dave Jones , Paul Gortmaker Subject: Re: 5.8-rc*: kernel BUG at kernel/signal.c:1917 Message-ID: <20200720084106.GJ10769@hirez.programming.kicks-ass.net> References: <6b253b55-586d-0bc4-9f58-c45c631abc60@kernel.org> <5a8c4c38-7aeb-981a-8d3b-a7a5c8ca5564@kernel.org> <20200717122651.GA6067@redhat.com> <20200717124017.GB6067@redhat.com> <2c8ef23c-43b4-39d4-8e84-92769c948da9@kernel.org> <20200718171406.GB16791@redhat.com> <20200718174448.4btbjcvp6wbbdgts@wittgenstein> <20200720064326.GA6612@redhat.com> <20200720082657.GC6612@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200720082657.GC6612@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 20, 2020 at 10:26:58AM +0200, Oleg Nesterov wrote: > Peter, > > Let me add another note. TASK_TRACED/TASK_STOPPED was always protected by > ->siglock. In particular, ttwu(__TASK_TRACED) must be always called with > ->siglock held. That is why ptrace_freeze_traced() assumes it can safely > do s/TASK_TRACED/__TASK_TRACED/ under spin_lock(siglock). > > Can this change race with > > if (signal_pending_state(prev->state, prev)) { > prev->state = TASK_RUNNING; > } > > in __schedule() ? Hopefully not, signal-state is protected by siglock too. > > So I think this logic was correct even if it doesn't look nice. But "doesn't > look nice" is true for the whole ptrace code ;) *groan*... another bit of obscure magic :-( let me go try and wake up and figure out how best to deal with this.