From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f199.google.com (mail-qt0-f199.google.com [209.85.216.199]) by kanga.kvack.org (Postfix) with ESMTP id 723B46B0009 for ; Thu, 15 Mar 2018 11:02:05 -0400 (EDT) Received: by mail-qt0-f199.google.com with SMTP id z1so4600727qtz.12 for ; Thu, 15 Mar 2018 08:02:05 -0700 (PDT) Received: from mx1.redhat.com (mx3-rdu2.redhat.com. [66.187.233.73]) by mx.google.com with ESMTPS id u20si5548479qth.231.2018.03.15.08.02.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 15 Mar 2018 08:02:03 -0700 (PDT) Date: Thu, 15 Mar 2018 16:01:57 +0100 From: Oleg Nesterov Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference count (semaphore) Message-ID: <20180315150156.GA19767@redhat.com> References: <20180313125603.19819-1-ravi.bangoria@linux.vnet.ibm.com> <20180313125603.19819-6-ravi.bangoria@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180313125603.19819-6-ravi.bangoria@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Ravi Bangoria 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 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(); Oleg.