Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932129AbcDNMTr (ORCPT ); Thu, 14 Apr 2016 08:19:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60189 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755137AbcDNMTo (ORCPT ); Thu, 14 Apr 2016 08:19:44 -0400 From: Xunlei Pang To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Juri Lelli , Ingo Molnar , Steven Rostedt , Xunlei Pang Subject: [PATCH] sched/deadline: Fix a bug in dl_overflow() Date: Thu, 14 Apr 2016 20:19:28 +0800 Message-Id: <1460636368-1993-1-git-send-email-xlpang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1679 Lines: 49 I got a minus(very big) dl_b->total_bw during my deadline tests. # grep dl /proc/sched_debug dl_rq[0]: .dl_nr_running : 0 .dl_bw->bw : 996147 .dl_bw->total_bw : -222297900 Something unusual must have happened. After some digging, I finally noticed that when changing a deadline task to normal(cfs), and changing it back to deadline immediately, after it died, we will got the wrong dl_bw->total_bw. The root cause is in dl_overflow(), it has: if (new_bw == p->dl.dl_bw) return 0; 1) When a deadline task is changed to !deadline task, it will start dl timer in switched_from_dl(), and retain previous deadline parameter till the timer expires. 2) If we change it back to deadline with the same bandwidth parameter before the timer expires, as it keeps the old bandwidth although it is not a deadline task. dl_overflow() simply returns success without updating the right data, and got the wrong dl_bw->total_bw. The solution is simple, if @p is not deadline, don't return. Signed-off-by: Xunlei Pang --- kernel/sched/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4a2c79d..5988fee 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2378,7 +2378,8 @@ static int dl_overflow(struct task_struct *p, int policy, u64 new_bw = dl_policy(policy) ? to_ratio(period, runtime) : 0; int cpus, err = -1; - if (new_bw == p->dl.dl_bw) + /* !deadline task may carry old deadline bandwidth */ + if (new_bw == p->dl.dl_bw && task_has_dl_policy(p)) return 0; /* -- 1.8.3.1