Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757585AbbGQL4e (ORCPT ); Fri, 17 Jul 2015 07:56:34 -0400 Received: from szxga02-in.huawei.com ([119.145.14.65]:53041 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756457AbbGQL4V (ORCPT ); Fri, 17 Jul 2015 07:56:21 -0400 Message-ID: <55A8ED0F.2040208@huawei.com> Date: Fri, 17 Jul 2015 19:54:55 +0800 From: "Wangnan (F)" User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Peter Zijlstra CC: kaixu xia , , , , , , , , , Subject: Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map References: <1437129816-13176-1-git-send-email-xiakaixu@huawei.com> <1437129816-13176-4-git-send-email-xiakaixu@huawei.com> <20150717110623.GK12596@twins.programming.kicks-ass.net> <55A8E554.9040205@huawei.com> <55A8E83E.6090506@huawei.com> <20150717114054.GE19282@twins.programming.kicks-ass.net> In-Reply-To: <20150717114054.GE19282@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.111.66.109] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1695 Lines: 53 On 2015/7/17 19:40, Peter Zijlstra wrote: > On Fri, Jul 17, 2015 at 07:34:22PM +0800, Wangnan (F) wrote: >> On 2015/7/17 19:21, Wangnan (F) wrote: >>> On 2015/7/17 19:06, Peter Zijlstra wrote: >>>> On Fri, Jul 17, 2015 at 06:43:33PM +0800, kaixu xia wrote: >>>>> diff --git a/kernel/events/core.c b/kernel/events/core.c >>>>> index e965cfa..c4e34b7 100644 >>>>> --- a/kernel/events/core.c >>>>> +++ b/kernel/events/core.c >>>>> @@ -8582,6 +8582,28 @@ void perf_event_delayed_put(struct task_struct >>>>> *task) >>>>> WARN_ON_ONCE(task->perf_event_ctxp[ctxn]); >>>>> } >>>>> +struct perf_event *perf_event_get(unsigned int fd) >>>>> +{ >>>>> + struct perf_event *event; >>>>> + struct fd f; >>>>> + >>>>> + f = fdget(fd); >>>>> + >>>>> + if (!f.file) >>>>> + return ERR_PTR(-EBADF); >>>>> + >>>>> + if (f.file->f_op != &perf_fops) { >>>>> + fdput(f); >>>>> + return ERR_PTR(-EINVAL); >>>>> + } >>>>> + >>>>> + event = f.file->private_data; >>>>> + >>>>> + fdput(f); >>>>> + >>>>> + return event; >>>>> +} >>>> And what is stopping userspace from closing those FDs while you're using >>>> them? >> Shall we put atomic_long_inc_not_zero() between fdget() and fdput()? > You pretty much _have_ to do that. Thanks. In next version we will introduce a new function which do oppsite thing to perf_event_release_kernel() in perf/event/core.c, then fetch the event before fdput. Thank you. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/