Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757553AbcJXMW5 (ORCPT ); Mon, 24 Oct 2016 08:22:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50034 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757230AbcJXMW4 (ORCPT ); Mon, 24 Oct 2016 08:22:56 -0400 Date: Mon, 24 Oct 2016 14:21:23 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: "Ni, BaoleX" , "mingo@redhat.com" , "acme@kernel.org" , "linux-kernel@vger.kernel.org" , "alexander.shishkin@linux.intel.com" , "Liu, Chuansheng" Subject: Re: hit a KASan bug related to Perf during stress test Message-ID: <20161024122123.GB17007@redhat.com> References: <318B87A793BE164187D8851D6CE09D64371C8811@shsmsx102.ccr.corp.intel.com> <20161024095341.GF3102@twins.programming.kicks-ass.net> <20161024111526.GA13509@redhat.com> <20161024121155.GK3102@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161024121155.GK3102@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.18 (2008-05-17) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Mon, 24 Oct 2016 12:22:55 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 925 Lines: 27 On 10/24, Peter Zijlstra wrote: > > On Mon, Oct 24, 2016 at 01:15:27PM +0200, Oleg Nesterov wrote: > > > > --- x/kernel/events/core.c > > +++ x/kernel/events/core.c > > @@ -1257,7 +1257,7 @@ static u32 perf_event_pid(struct perf_ev > > if (event->parent) > > event = event->parent; > > > > - return task_tgid_nr_ns(p, event->ns); > > + return pid_alive(p) ? task_tgid_nr_ns(p, event->ns) : 0; > > } > > > > static u32 perf_event_tid(struct perf_event *event, struct task_struct *p) > > Should we do the same for perf_event_tid() and report -1 as the pid/tid > in the !alive case? -1 should be an obvious invalid pid since we limit > the pid-space to less than 32 bits. task_pid_nr_ns() is always safe, it calls __task_pid_nr_ns(). But yes, it can return zero if called after exit_notify() and/or release_task(). And while zero is not a valid pid too, I guess it can be confused with the idle thread's "pid" ? Oleg.