From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754851AbcHVKia (ORCPT ); Mon, 22 Aug 2016 06:38:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52274 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754333AbcHVKi2 (ORCPT ); Mon, 22 Aug 2016 06:38:28 -0400 Date: Mon, 22 Aug 2016 12:38:23 +0200 From: Jiri Olsa To: Vegard Nossum , Peter Zijlstra Cc: Thomas Gleixner , Stephane Eranian , Vince Weaver , Ingo Molnar , David Carrillo-Cisneros , "H. Peter Anvin" , Kan Liang , Arnaldo Carvalho de Melo , Paul Turner , Linus Torvalds , LKML , Alexander Shishkin , linux-tip-commits@vger.kernel.org Subject: Re: [tip:perf/core] perf/core: Check return value of the perf_event_read() IPI Message-ID: <20160822103823.GA2271@krava> References: <1471467307-61171-2-git-send-email-davidcc@google.com> <20160822071737.GF4349@krava> <20160822082932.GA13171@krava> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160822082932.GA13171@krava> User-Agent: Mutt/1.7.0 (2016-08-17) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Mon, 22 Aug 2016 10:38:27 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 22, 2016 at 10:29:32AM +0200, Jiri Olsa wrote: > On Mon, Aug 22, 2016 at 09:17:37AM +0200, Jiri Olsa wrote: > > On Sun, Aug 21, 2016 at 02:10:07PM +0200, Vegard Nossum wrote: > > > > SNIP > > > > > [] ? __fget+0x47/0x270 > > > [] vfs_readv+0x8b/0xc0 > > > [] do_readv+0xde/0x230 > > > [] ? vfs_readv+0xc0/0xc0 > > > [] ? exit_to_usermode_loop+0x190/0x190 > > > [] ? check_preemption_disabled+0x37/0x1e0 > > > [] SyS_readv+0x27/0x30 > > > [] ? do_pwritev+0x1a0/0x1a0 > > > [] do_syscall_64+0x1c4/0x4e0 > > > [] entry_SYSCALL64_slow_path+0x25/0x25 > > > > > > I don't think WARN() is the right interface for signalling errors to > > > userspace programs? > > > > any special way to trigger that? > > nope ;-) > > perf stat -a -I 10 reading the event could race with event schedule out leaving us with active state and oncpu == -1 attached patch fixes the warn for me, but I might be missing some other cases jirka --- diff --git a/kernel/events/core.c b/kernel/events/core.c index 3f07e6cfc1b6..375274b6f3b4 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1802,8 +1802,9 @@ event_sched_out(struct perf_event *event, event->tstamp_stopped = tstamp; event->pmu->del(event, 0); - event->oncpu = -1; - event->state = PERF_EVENT_STATE_INACTIVE; + WRITE_ONCE(event->state, PERF_EVENT_STATE_INACTIVE); + smp_wmb(); + WRITE_ONCE(event->oncpu, -1); if (event->pending_disable) { event->pending_disable = 0; event->state = PERF_EVENT_STATE_OFF; @@ -3424,9 +3425,8 @@ struct perf_read_data { int ret; }; -static int find_cpu_to_read(struct perf_event *event, int local_cpu) +static int find_cpu_to_read(struct perf_event *event, int event_cpu, int local_cpu) { - int event_cpu = event->oncpu; u16 local_pkg, event_pkg; if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) { @@ -3561,13 +3561,17 @@ u64 perf_event_read_local(struct perf_event *event) static int perf_event_read(struct perf_event *event, bool group) { - int ret = 0, cpu_to_read, local_cpu; + int ret = 0, cpu_to_read, local_cpu, state; + + state = READ_ONCE(event->state); + smp_rmb(); + cpu_to_read = event->oncpu; /* * If event is enabled and currently active on a CPU, update the * value in the event structure: */ - if (event->state == PERF_EVENT_STATE_ACTIVE) { + if (state == PERF_EVENT_STATE_ACTIVE && cpu_to_read != -1) { struct perf_read_data data = { .event = event, .group = group, @@ -3575,7 +3579,7 @@ static int perf_event_read(struct perf_event *event, bool group) }; local_cpu = get_cpu(); - cpu_to_read = find_cpu_to_read(event, local_cpu); + cpu_to_read = find_cpu_to_read(event, cpu_to_read, local_cpu); put_cpu(); ret = smp_call_function_single(cpu_to_read, __perf_event_read, &data, 1);