From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753823AbbK3L4V (ORCPT ); Mon, 30 Nov 2015 06:56:21 -0500 Received: from casper.infradead.org ([85.118.1.10]:47997 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751018AbbK3L4T (ORCPT ); Mon, 30 Nov 2015 06:56:19 -0500 Date: Mon, 30 Nov 2015 12:56:15 +0100 From: Peter Zijlstra To: Dmitry Vyukov Cc: Ingo Molnar , Arnaldo Carvalho de Melo , LKML , syzkaller , Alexander Potapenko , Kostya Serebryany , Eric Dumazet , Sasha Levin Subject: Re: deadlock in perf_ioctl Message-ID: <20151130115615.GJ17308@twins.programming.kicks-ass.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 30, 2015 at 10:20:49AM +0100, Dmitry Vyukov wrote: > ============================================= > [ INFO: possible recursive locking detected ] > 4.4.0-rc1+ #129 Not tainted > --------------------------------------------- > a.out/6283 is trying to acquire lock: > (&ctx->lock){-.....}, at: [] > __perf_event_period+0x8e/0x4b0 kernel/events/core.c:4156 > > but task is already holding lock: > (&ctx->lock){-.....}, at: [< inline >] perf_event_period > kernel/events/core.c:4212 > (&ctx->lock){-.....}, at: [< inline >] _perf_ioctl > kernel/events/core.c:4266 > (&ctx->lock){-.....}, at: [] perf_ioctl+0x7bc/0xcc0 > kernel/events/core.c:4320 > Indeed so. I suppose the below should fix this, I'll go try in a bit. --- Subject: perf: Fix PERF_EVENT_IOC_PERIOD deadlock Dmitry reported a fairly silly recursive lock deadlock for PERF_EVENT_IOC_PERIOD, fix this by explicitly doing the inactive part of __perf_event_period() instead of calling that function. Reported-by: Dmitry Vyukov Fixes: c7999c6f3fed ("perf: Fix PERF_EVENT_IOC_PERIOD migration race") Signed-off-by: Peter Zijlstra (Intel) --- kernel/events/core.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 36babfd20648..a991e12e4d0d 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4216,7 +4216,14 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg) goto retry; } - __perf_event_period(&pe); + if (event->attr.freq) { + event->attr.sample_freq = value; + } else { + event->attr.sample_period = value; + event->hw.sample_period = value; + } + + local64_set(&event->hw.period_left, 0); raw_spin_unlock_irq(&ctx->lock); return 0;