From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 59AF16B0009 for ; Fri, 16 Mar 2018 05:28:58 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id y145so499372wmd.4 for ; Fri, 16 Mar 2018 02:28:58 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id i40si3116838ede.65.2018.03.16.02.28.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 16 Mar 2018 02:28:57 -0700 (PDT) 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 w2G9OQYG003404 for ; Fri, 16 Mar 2018 05:28:55 -0400 Received: from e06smtp10.uk.ibm.com (e06smtp10.uk.ibm.com [195.75.94.106]) by mx0a-001b2d01.pphosted.com with ESMTP id 2gr9tkbmnd-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Fri, 16 Mar 2018 05:28:55 -0400 Received: from localhost by e06smtp10.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 16 Mar 2018 09:28:53 -0000 Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference count (semaphore) References: <20180313125603.19819-1-ravi.bangoria@linux.vnet.ibm.com> <20180313125603.19819-6-ravi.bangoria@linux.vnet.ibm.com> <20180315150156.GA19767@redhat.com> From: Ravi Bangoria Date: Fri, 16 Mar 2018 15:01:05 +0530 MIME-Version: 1.0 In-Reply-To: <20180315150156.GA19767@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US Message-Id: Sender: owner-linux-mm@kvack.org List-ID: To: Oleg Nesterov 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, Ravi Bangoria On 03/15/2018 08:31 PM, Oleg Nesterov wrote: > On 03/13, Ravi Bangoria wrote: >> +sdt_update_ref_ctr(struct mm_struct *mm, unsigned long vaddr, short d) >> +{ >> + void *kaddr; >> + struct page *page; >> + struct vm_area_struct *vma; >> + int ret = 0; >> + unsigned short orig = 0; >> + >> + if (vaddr == 0) >> + return -EINVAL; >> + >> + ret = get_user_pages_remote(NULL, mm, vaddr, 1, >> + FOLL_FORCE | FOLL_WRITE, &page, &vma, NULL); >> + if (ret <= 0) >> + return ret; >> + >> + kaddr = kmap_atomic(page); >> + memcpy(&orig, kaddr + (vaddr & ~PAGE_MASK), sizeof(orig)); >> + orig += d; >> + memcpy(kaddr + (vaddr & ~PAGE_MASK), &orig, sizeof(orig)); >> + kunmap_atomic(kaddr); > Hmm. Why memcpy? You could simply do > > kaddr = kmap_atomic(); > unsigned short *ptr = kaddr + (vaddr & ~PAGE_MASK); > *ptr += d; > kunmap_atomic(); Yes, that should work. Will change it. Thanks for the review, Ravi