From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Mon, 13 Aug 2018 13:50:35 +0200 (CEST) Received: from mx3-rdu2.redhat.com ([66.187.233.73]:52144 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by eddie.linux-mips.org with ESMTP id S23993057AbeHMLuaDtDmU (ORCPT ); Mon, 13 Aug 2018 13:50:30 +0200 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 9C4A940122B3; Mon, 13 Aug 2018 11:50:23 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id 738F52026D66; Mon, 13 Aug 2018 11:50:20 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 13 Aug 2018 13:50:23 +0200 (CEST) Date: Mon, 13 Aug 2018 13:50:19 +0200 From: Oleg Nesterov To: Ravi Bangoria 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 Subject: Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore) Message-ID: <20180813115019.GB28360@redhat.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <95a1221e-aecc-42be-5239-a2c2429be176@linux.ibm.com> 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 [10.11.55.5]); Mon, 13 Aug 2018 11:50:23 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Mon, 13 Aug 2018 11:50:23 +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:'' 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: 65562 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: oleg@redhat.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 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. > >> + 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(). Afaics, the really problematic case is dlopen() which can race with _register() too, right? Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 From: oleg@redhat.com (Oleg Nesterov) Date: Mon, 13 Aug 2018 13:50:19 +0200 Subject: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore) In-Reply-To: <95a1221e-aecc-42be-5239-a2c2429be176@linux.ibm.com> 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> Message-ID: <20180813115019.GB28360@redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. > >> + 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(). Afaics, the really problematic case is dlopen() which can race with _register() too, right? Oleg.