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 3AC1A7DE74 for ; Tue, 8 May 2018 10:26:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754690AbeEHK0m (ORCPT ); Tue, 8 May 2018 06:26:42 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:48458 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754677AbeEHK0l (ORCPT ); Tue, 8 May 2018 06:26:41 -0400 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w48APHFO060000 for ; Tue, 8 May 2018 06:26:40 -0400 Received: from e06smtp11.uk.ibm.com (e06smtp11.uk.ibm.com [195.75.94.107]) by mx0b-001b2d01.pphosted.com with ESMTP id 2hu6kx24gh-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 08 May 2018 06:26:40 -0400 Received: from localhost by e06smtp11.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Tue, 8 May 2018 11:26:30 +0100 Received: from d06av24.portsmouth.uk.ibm.com (d06av24.portsmouth.uk.ibm.com [9.149.105.60]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w48AQUwV10813782; Tue, 8 May 2018 10:26:30 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 88C6442041; Tue, 8 May 2018 11:17:33 +0100 (BST) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 008784203F; Tue, 8 May 2018 11:17:29 +0100 (BST) Received: from [9.124.31.153] (unknown [9.124.31.153]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 8 May 2018 11:17:28 +0100 (BST) From: Ravi Bangoria Subject: Re: [PATCH v3 6/9] trace_uprobe: Support SDT markers having reference count (semaphore) To: Masami Hiramatsu Cc: oleg@redhat.com, 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 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> <20180508005651.45553d3cf72521481d16b801@kernel.org> Date: Tue, 8 May 2018 15:56:24 +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: <20180508005651.45553d3cf72521481d16b801@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-TM-AS-GCONF: 00 x-cbid: 18050810-0040-0000-0000-0000045740E3 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18050810-0041-0000-0000-000020FB4507 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-05-08_04:,, 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=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1805080100 Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Masami, On 05/07/2018 09:26 PM, Masami Hiramatsu wrote: > On Mon, 7 May 2018 13:51:21 +0530 > Ravi Bangoria wrote: > >> 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. > Hmm, can't you roll that back if sdt_increment_ref_ctr() fails? > If so, how does sdt_decrement_ref_ctr() work in that case? Yes, it's easy to rollback in sdt_increment_ref_ctr(). But not much can be done if trace_uprobe_mmap() fails. What would be good is, if we can feedback uprobe_mmap() failures to the perf infrastructure, which can finally be parsed by perf record. But that should be done as a separate work. >> 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). > Of course we need to warn it at least, but the best is rejecting to > enable it. Yes, we can reject it for sdt_increment_ref_ctr() failures. >> 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 > Oops, that's a real bug. It seems the ball is in Naveen's hand. > Naveen, could you update it according to Oleg's comment, and resend it? > >> 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. > I see. Please carefully clarify whether such case is kernel's bug or not. > I would like to know what the condition causes that uneven behavior. Sure, will do that. Thanks, Ravi -- 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