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 3AE8FC433EF for ; Mon, 2 May 2022 09:06:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1383974AbiEBJJu (ORCPT ); Mon, 2 May 2022 05:09:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42194 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354638AbiEBJJf (ORCPT ); Mon, 2 May 2022 05:09:35 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 42A1965B1 for ; Mon, 2 May 2022 02:06:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1651482366; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YnxLMDZpimSJvf7sCwd+c/i6sHfHGWF3GvvV71348bQ=; b=VBoyU85kIjvg/rJBFLNmH/ldIvNEjvtDDRziXB49FtOS3UNyXW9g1UH9hdkRQzqVfTBQYK rAtNJyBuw3Ta3+qJLO1EtnMrS47Vl9yi0ntCr9OFt9oqYj4rjhYbP7ZD2jFuL6rYFv9//R TNkIZ/CukHnu/zDyVwqoZokyA9zY06M= 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-487-1HEnjXepNDi8fKSdmHrwiw-1; Mon, 02 May 2022 05:06:05 -0400 X-MC-Unique: 1HEnjXepNDi8fKSdmHrwiw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E261B800186; Mon, 2 May 2022 09:06:04 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.193.70]) by smtp.corp.redhat.com (Postfix) with SMTP id D8F8914C3018; Mon, 2 May 2022 09:06:03 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 2 May 2022 11:06:01 +0200 (CEST) Date: Mon, 2 May 2022 11:06:00 +0200 From: Oleg Nesterov To: Shuzhi Zu Cc: brauner@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] signal/ptrace: Fix the bug of ptrace attach and signal handling concurrency Message-ID: <20220502090559.GA17276@redhat.com> References: <20220430165556.29739-1-zushuzhi@h3c.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220430165556.29739-1-zushuzhi@h3c.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.7 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Shuzhi, On 05/01, Shuzhi Zu wrote: > > Example 1： > A B > get_signal > dequeue_signal (SIGCHLD） > ptrace_attach ( A->ptrace |= PT_PTRACED) > > ptrace_signal > ->ptrace_stop(TASK_TRACED) > ptrace_attach ( Send SIGSTOP to A) > ptrace_waitpid( return 0) > ptrace_detach (A->ptrace=0, wakeup A) > dequeue_signal(SIGSTOP) > sig_kernel_stop(SIGSTOP) > do_signal_stop (TASK_STOPPED) > > then： > A (other threads of the process received signal) > get_signal-> do_signal_stop(0))->TASK_STOPPED Yes, there are a lot of known problems with send_sig_info(SIGSTOP) in ptrace_attach(). This one of the reasons for PTRACE_SEIZE which doesn't abuse SIGSTOP. Please use it instead of PTRACE_ATTACH, PTRACE_SEIZE has more features. As for your particular example, this is an application bug. Debugger (if it uses PTRACE_ATTACH) should not detach until the tracee reports SIGSTOP sent by PTRACE_ATTACH. This can lead to other problems, say we can miss a "real" SIGSTOP from another application, but again PTRACE_ATTACH is hopeless wrt SIGSTOP, please consider PTRACE_SEIZE. Oleg.