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 E4DD3C433F5 for ; Wed, 27 Apr 2022 14:10:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237416AbiD0OOF (ORCPT ); Wed, 27 Apr 2022 10:14:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60560 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237600AbiD0ON7 (ORCPT ); Wed, 27 Apr 2022 10:13:59 -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 BD644506F6 for ; Wed, 27 Apr 2022 07:10:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1651068641; 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=NKhDa4ztHhyXVoYawVPKdjEeIt2vB/BQ7DGgaiHHY0s=; b=httw3I3SiwwJLIUbsF2NxjF/SFIzX9fQG7P2E7UPi5FjusMc+hYQXoOe/V25kIc83HFrGS m8C7mSGz/9Badn+ZDgCGGjgHt6Ljl4Zf3ScLUMaz12+BHYbT5E0uiIKHkckSKbQ6yLZiN+ vbY71Z+joWfRE85qMXhrGL3K0FYFMPI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-312-f6f79C7nO12uafBPvmz1SA-1; Wed, 27 Apr 2022 10:10:34 -0400 X-MC-Unique: f6f79C7nO12uafBPvmz1SA-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3211B1014A61; Wed, 27 Apr 2022 14:10:33 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.128]) by smtp.corp.redhat.com (Postfix) with SMTP id 0C5E257C911; Wed, 27 Apr 2022 14:10:27 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 27 Apr 2022 16:10:31 +0200 (CEST) Date: Wed, 27 Apr 2022 16:10:25 +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: <20220427141018.GA17421@redhat.com> References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-6-ebiederm@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220426225211.308418-6-ebiederm@xmission.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 04/26, Eric W. Biederman wrote: > > @@ -2164,7 +2166,9 @@ static void do_notify_parent_cldstop(struct task_struct *tsk, > } > > sighand = parent->sighand; > - spin_lock_irqsave(&sighand->siglock, flags); > + lock = tsk->sighand != sighand; > + if (lock) > + spin_lock_nested(&sighand->siglock, SINGLE_DEPTH_NESTING); But why is it safe? Suppose we have two tasks, they both trace each other, both call ptrace_stop() at the same time. Of course this is ugly, they both will block. But with this patch in this case we have the trivial ABBA deadlock, no? Oleg.