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=-4.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, RCVD_IN_DNSWL_HI,T_RP_MATCHES_RCVD 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 365057E677 for ; Fri, 16 Mar 2018 17:50:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751511AbeCPRui (ORCPT ); Fri, 16 Mar 2018 13:50:38 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:32860 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751454AbeCPRuh (ORCPT ); Fri, 16 Mar 2018 13:50:37 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 912F481A8123; Fri, 16 Mar 2018 17:50:36 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id 76503202322B; Fri, 16 Mar 2018 17:50:31 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 16 Mar 2018 18:50:36 +0100 (CET) Date: Fri, 16 Mar 2018 18:50:30 +0100 From: Oleg Nesterov To: Ravi Bangoria Cc: mhiramat@kernel.org, peterz@infradead.org, srikar@linux.vnet.ibm.com, 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, gregkh@linuxfoundation.org, huawei.libin@huawei.com, hughd@google.com, jack@suse.cz, jglisse@redhat.com, jolsa@redhat.com, kan.liang@intel.com, kirill.shutemov@linux.intel.com, kjlx@templeofstupid.com, kstewart@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, milian.wolff@kdab.com, mingo@redhat.com, namhyung@kernel.org, naveen.n.rao@linux.vnet.ibm.com, pc@us.ibm.com, pombredanne@nexb.com, rostedt@goodmis.org, tglx@linutronix.de, tmricht@linux.vnet.ibm.com, willy@infradead.org, yao.jin@linux.intel.com, fengguang.wu@intel.com Subject: Re: [PATCH 6/8] trace_uprobe/sdt: Fix multiple update of same reference counter Message-ID: <20180316175030.GA28770@redhat.com> References: <20180313125603.19819-1-ravi.bangoria@linux.vnet.ibm.com> <20180313125603.19819-7-ravi.bangoria@linux.vnet.ibm.com> <20180315144959.GB19643@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 16 Mar 2018 17:50:36 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 16 Mar 2018 17:50:36 +0000 (UTC) for IP:'10.11.54.4' DOMAIN:'int-mx04.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 On 03/16, Ravi Bangoria wrote: > > On 03/15/2018 08:19 PM, Oleg Nesterov wrote: > > On 03/13, Ravi Bangoria wrote: > >> For tiny binaries/libraries, different mmap regions points to the > >> same file portion. In such cases, we may increment reference counter > >> multiple times. > > Yes, > > > >> But while de-registration, reference counter will get > >> decremented only by once > > could you explain why this happens? sdt_increment_ref_ctr() and > > sdt_decrement_ref_ctr() look symmetrical, _decrement_ should see > > the same mappings? ... >     # strace -o out python >       mmap(NULL, 2738968, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fff92460000 >       mmap(0x7fff926a0000, 327680, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x230000) = 0x7fff926a0000 >       mprotect(0x7fff926a0000, 65536, PROT_READ) = 0 Ah, in this case everything is clear, thanks. I was confused by the changelog, I misinterpreted it as if inc/dec are not balanced in case of multiple mappings even if the application doesn't play with mmap/mprotect/etc. And it seems that you are trying to confuse yourself, not only me ;) Just suppose that an application does mmap+munmap in a loop and the mapped region contains uprobe but not the counter. And this all makes me think that we should do something else. Ideally, install_breakpoint() and remove_breakpoint() should inc/dec the counter if they do not fail... Btw, why do we need a counter, not a boolean? Who else can modify it? Or different uprobes can share the same counter? 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