From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 9CDA87DF9C for ; Thu, 24 May 2018 16:26:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1033626AbeEXQ0U (ORCPT ); Thu, 24 May 2018 12:26:20 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:42426 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1033618AbeEXQ0O (ORCPT ); Thu, 24 May 2018 12:26:14 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9D1D87D859; Thu, 24 May 2018 16:26:13 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id B1A981102E29; Thu, 24 May 2018 16:26:08 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 24 May 2018 18:26:13 +0200 (CEST) Date: Thu, 24 May 2018 18:26:08 +0200 From: Oleg Nesterov To: Ravi Bangoria Cc: mhiramat@kernel.org, peterz@infradead.org, srikar@linux.vnet.ibm.com, rostedt@goodmis.org, acme@kernel.org, ananth@linux.vnet.ibm.com, akpm@linux-foundation.org, alexander.shishkin@linux.intel.com, alexis.berlemont@gmail.com, corbet@lwn.net, dan.j.williams@intel.com, jolsa@redhat.com, kan.liang@intel.com, kjlx@templeofstupid.com, kstewart@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, milian.wolff@kdab.com, mingo@redhat.com, namhyung@kernel.org, naveen.n.rao@linux.vnet.ibm.com, pc@us.ibm.com, tglx@linutronix.de, yao.jin@linux.intel.com, fengguang.wu@intel.com, jglisse@redhat.com, Ravi Bangoria Subject: Re: [PATCH v3 6/9] trace_uprobe: Support SDT markers having reference count (semaphore) Message-ID: <20180524162608.GA27082@redhat.com> References: <20180417043244.7501-1-ravi.bangoria@linux.vnet.ibm.com> <20180417043244.7501-7-ravi.bangoria@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180417043244.7501-7-ravi.bangoria@linux.vnet.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Thu, 24 May 2018 16:26:13 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Thu, 24 May 2018 16:26:13 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'oleg@redhat.com' RCPT:'' Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Ravi, sorry for delay! I am trying to recall what this code should do ;) At first glance, I do not see any serious problem in this version... except it doesn't apply to Linus's tree. just one question for now. On 04/17, Ravi Bangoria wrote: > > @@ -941,6 +1091,9 @@ typedef bool (*filter_func_t)(struct uprobe_consumer *self, > if (ret) > goto err_buffer; > > + if (tu->ref_ctr_offset) > + sdt_increment_ref_ctr(tu); > + iiuc, this is probe_event_enable()... Looks racy, but afaics the race with uprobe_mmap() will be closed by the next change. However, it seems that probe_event_disable() can race with trace_uprobe_mmap() too and the next 7/9 patch won't help, > + if (tu->ref_ctr_offset) > + sdt_decrement_ref_ctr(tu); > + > uprobe_unregister(tu->inode, tu->offset, &tu->consumer); > tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE; so what if trace_uprobe_mmap() comes right after uprobe_unregister() ? Note that trace_probe_is_enabled() is T until we update tp.flags. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html