From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Mon, 13 Aug 2018 15:01:20 +0200 (CEST) Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:35902 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by eddie.linux-mips.org with ESMTP id S23992869AbeHMNBRX-iK9 (ORCPT ); Mon, 13 Aug 2018 15:01:17 +0200 Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w7DD01eE112537 for ; Mon, 13 Aug 2018 09:01:15 -0400 Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com [195.75.94.103]) by mx0a-001b2d01.pphosted.com with ESMTP id 2ku9th9ntm-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 13 Aug 2018 09:01:15 -0400 Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 13 Aug 2018 14:01:07 +0100 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w7DD16Kg46137524 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 13 Aug 2018 13:01:06 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id EBE69A4065; Mon, 13 Aug 2018 16:01:10 +0100 (BST) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 53B24A4055; Mon, 13 Aug 2018 16:01:06 +0100 (BST) Received: from [9.79.223.161] (unknown [9.79.223.161]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 13 Aug 2018 16:01:06 +0100 (BST) From: Ravi Bangoria Subject: Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore) To: Oleg Nesterov Cc: Song Liu , srikar@linux.vnet.ibm.com, Steven Rostedt , mhiramat@kernel.org, Peter Zijlstra , mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, open list , ananth@linux.vnet.ibm.com, Alexis Berlemont , naveen.n.rao@linux.vnet.ibm.com, linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org, linux@armlinux.org.uk, ralf@linux-mips.org, paul.burton@mips.com, Ravi Bangoria References: <20180809041856.1547-1-ravi.bangoria@linux.ibm.com> <20180809041856.1547-4-ravi.bangoria@linux.ibm.com> <95a1221e-aecc-42be-5239-a2c2429be176@linux.ibm.com> <20180813115019.GB28360@redhat.com> Date: Mon, 13 Aug 2018 18:31:00 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180813115019.GB28360@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18081313-0028-0000-0000-000002EA1227 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18081313-0029-0000-0000-000023A32D9D Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-08-13_05:,, 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 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1808130142 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 65563 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ravi.bangoria@linux.ibm.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips Hi Oleg, On 08/13/2018 05:20 PM, Oleg Nesterov wrote: > On 08/13, Ravi Bangoria wrote: >> >> On 08/11/2018 01:27 PM, Song Liu wrote: >>>> + >>>> +static void delayed_uprobe_delete(struct delayed_uprobe *du) >>>> +{ >>>> + if (!du) >>>> + return; >>> Do we really need this check? >> >> Not necessary though, but I would still like to keep it for a safety. > > Heh. I tried to ignore all minor problems in this version, but now that Song > mentioned this unnecessary check... > > Personally I really dislike the checks like this one. > > - It can confuse the reader who will try to understand the purpose > > - it can hide a bug if delayed_uprobe_delete(du) is actually called > with du == NULL. > > IMO, you should either remove it and let the kernel crash (to notice the > problem), or turn it into > > if (WARN_ON(!du)) > return; > > which is self-documented and reports the problem without kernel crash. Ok. I'll remove that check. > >>>> + rc_vma = find_ref_ctr_vma(uprobe, mm); >>>> + >>>> + if (rc_vma) { >>>> + rc_vaddr = offset_to_vaddr(rc_vma, uprobe->ref_ctr_offset); >>>> + ret = __update_ref_ctr(mm, rc_vaddr, is_register ? 1 : -1); >>>> + >>>> + if (is_register) >>>> + return ret; >>>> + } >>> Mixing __update_ref_ctr() here and delayed_uprobe_add() in the same >>> function is a little confusing (at least for me). How about we always use >>> delayed uprobe for uprobe_mmap() and use non-delayed in other case(s)? >> >> >> No. delayed_uprobe_add() is needed for uprobe_register() case to handle race >> between uprobe_register() and process creation. > > Yes. > > But damn, process creation (exec) is trivial. We could add a new uprobe_exec() > hook and avoid delayed_uprobe_install() in uprobe_mmap(). I'm sorry. I didn't get this. > > Afaics, the really problematic case is dlopen() which can race with _register() > too, right? dlopen() should internally use mmap() right? So what is the problem here? Can you please elaborate. Thanks, Ravi