From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752115AbeEGIWH (ORCPT ); Mon, 7 May 2018 04:22:07 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:49992 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751988AbeEGIVf (ORCPT ); Mon, 7 May 2018 04:21:35 -0400 Subject: Re: [PATCH v3 6/9] trace_uprobe: Support SDT markers having reference count (semaphore) From: Ravi Bangoria To: Masami Hiramatsu , oleg@redhat.com Cc: Ravi Bangoria , 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 References: <20180417043244.7501-1-ravi.bangoria@linux.vnet.ibm.com> <20180417043244.7501-7-ravi.bangoria@linux.vnet.ibm.com> <20180504134816.8633a157dd036489d9b0f1db@kernel.org> <206e4a16-ae21-7da3-f752-853dc2f51947@linux.ibm.com> Date: Mon, 7 May 2018 13:51:21 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <206e4a16-ae21-7da3-f752-853dc2f51947@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-TM-AS-GCONF: 00 x-cbid: 18050708-0044-0000-0000-0000054FD511 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18050708-0045-0000-0000-000028910D76 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-05-07_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1805070086 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Masami, On 05/04/2018 07:51 PM, Ravi Bangoria wrote: > >>> +} >>> + >>> +static void sdt_increment_ref_ctr(struct trace_uprobe *tu) >>> +{ >>> + struct uprobe_map_info *info; >>> + >>> + uprobe_down_write_dup_mmap(); >>> + info = uprobe_build_map_info(tu->inode->i_mapping, >>> + tu->ref_ctr_offset, false); >>> + if (IS_ERR(info)) >>> + goto out; >>> + >>> + while (info) { >>> + down_write(&info->mm->mmap_sem); >>> + >>> + if (sdt_find_vma(tu, info->mm, info->vaddr)) >>> + sdt_update_ref_ctr(info->mm, info->vaddr, 1); >> Don't you have to handle the error to map pages here? > Correct.. I think, I've to feedback error code to probe_event_{enable|disable} > and handler failure there. I looked at this. Actually, It looks difficult to feedback errors to probe_event_{enable|disable}, esp. in the mmap() case. Is it fine if we just warn sdt_update_ref_ctr() failures in dmesg? I'm doing this in [PATCH 7]. (Though, it makes more sense to do that in [PATCH 6], will change it in next version). Any better ideas? BTW, same issue exists for normal uprobe. If uprobe_mmap() fails, there is no feedback to trace_uprobe and no warnigns in dmesg as well !! There was a patch by Naveen to warn such failures in dmesg but that didn't go in: https://lkml.org/lkml/2017/9/22/155 Also, I'll add a check in sdt_update_ref_ctr() to make sure reference counter never goes to negative incase increment fails but decrement succeeds. OTOH, if increment succeeds but decrement fails, the counter remains >0 but there is no harm as such, except we will execute some unnecessary code. Thanks, Ravi