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 9CDC5C433F5 for ; Wed, 27 Apr 2022 15:01:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238901AbiD0PEa (ORCPT ); Wed, 27 Apr 2022 11:04:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45820 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238888AbiD0PE1 (ORCPT ); Wed, 27 Apr 2022 11:04:27 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C46E627D178 for ; Wed, 27 Apr 2022 08:01:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1651071675; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Egehvqg27Nr6FMLxE+ww4T3/EHzKsHjYMiC2xu74Aa0=; b=LVaAvq3pUdzDDz4KdkbPEz2iAxUDvXcsUqC+oKrsPAkbeJWD19W+xU35PK+1Uz0M2EkxqT cxuBWTXcmzX1wHogjTb3Wxqv7NhwfoGFcOYhvTmHKqOFPrpezLbu7ZuRFV1dqQJLYg7AWS HweuLIL2lFEa0PQI+Z3r3tUjj6VT5Cw= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-220-bpgZATshNN-iftRBC2UfHA-1; Wed, 27 Apr 2022 11:01:12 -0400 X-MC-Unique: bpgZATshNN-iftRBC2UfHA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 13E673839772; Wed, 27 Apr 2022 15:01:00 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.128]) by smtp.corp.redhat.com (Postfix) with SMTP id 83842C4C7A1; Wed, 27 Apr 2022 15:00:55 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 27 Apr 2022 17:00:59 +0200 (CEST) Date: Wed, 27 Apr 2022 17:00:54 +0200 From: Oleg Nesterov To: "Eric W. Biederman" Cc: linux-kernel@vger.kernel.org, rjw@rjwysocki.net, 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, Peter Zijlstra , Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Chris Zankel , Max Filippov , inux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn Subject: Re: [PATCH 6/9] signal: Always call do_notify_parent_cldstop with siglock held Message-ID: <20220427150053.GD17421@redhat.com> References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-6-ebiederm@xmission.com> <20220427145646.GC17421@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220427145646.GC17421@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/27, Oleg Nesterov wrote: > > On 04/26, Eric W. Biederman wrote: > > > > @@ -2209,6 +2213,34 @@ static int ptrace_stop(int exit_code, int why, int clear_code, > > spin_lock_irq(¤t->sighand->siglock); > > } > > > > + /* Don't stop if current is not ptraced */ > > + if (unlikely(!current->ptrace)) > > + return (clear_code) ? 0 : exit_code; > > + > > + /* > > + * If @why is CLD_STOPPED, we're trapping to participate in a group > > + * stop. Do the bookkeeping. Note that if SIGCONT was delievered > > + * across siglock relocks since INTERRUPT was scheduled, PENDING > > + * could be clear now. We act as if SIGCONT is received after > > + * TASK_TRACED is entered - ignore it. > > + */ > > + if (why == CLD_STOPPED && (current->jobctl & JOBCTL_STOP_PENDING)) > > + gstop_done = task_participate_group_stop(current); > > + > > + /* > > + * Notify parents of the stop. > > + * > > + * While ptraced, there are two parents - the ptracer and > > + * the real_parent of the group_leader. The ptracer should > > + * know about every stop while the real parent is only > > + * interested in the completion of group stop. The states > > + * for the two don't interact with each other. Notify > > + * separately unless they're gonna be duplicates. > > + */ > > + do_notify_parent_cldstop(current, true, why); > > + if (gstop_done && ptrace_reparented(current)) > > + do_notify_parent_cldstop(current, false, why); > > This doesn't look right too. The parent should be notified only after > we set __state = TASK_TRACED and ->exit code. > > Suppose that debugger sleeps in do_wait(). do_notify_parent_cldstop() > wakes it up, debugger calls wait_task_stopped() and then it will sleep > again, task_stopped_code() returns 0. > > This can be probably fixed if you remove the lockless (fast path) > task_stopped_code() check in wait_task_stopped(), but this is not > nice performance-wise... On the other hand, I don't understand why did you move the callsite of do_notify_parent_cldstop() up... just don't do this? Oleg.