From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933055AbaEMMKm (ORCPT ); Tue, 13 May 2014 08:10:42 -0400 Received: from mail-we0-f181.google.com ([74.125.82.181]:33654 "EHLO mail-we0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759338AbaEMMKl (ORCPT ); Tue, 13 May 2014 08:10:41 -0400 Date: Tue, 13 May 2014 14:11:31 +0200 From: Juri Lelli To: Peter Zijlstra Cc: "Michael Kerrisk (man-pages)" , Dario Faggioli , Ingo Molnar , lkml , Dave Jones Subject: Re: [BUG] sched_setattr() SCHED_DEADLINE hangs system Message-Id: <20140513141131.20d944f81633ee937f256385@gmail.com> In-Reply-To: <20140513104307.GZ30445@twins.programming.kicks-ass.net> References: <536F8F0E.7020301@gmail.com> <53707007.3080003@gmail.com> <20140512084727.GN30445@twins.programming.kicks-ass.net> <20140512123032.GC13467@laptop.programming.kicks-ass.net> <20140513115749.ebf3eebc64e44aac6f183410@gmail.com> <20140513104307.GZ30445@twins.programming.kicks-ass.net> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 13 May 2014 12:43:07 +0200 Peter Zijlstra wrote: > On Tue, May 13, 2014 at 11:57:49AM +0200, Juri Lelli wrote: > > static bool > > __checkparam_dl(const struct sched_attr *attr) > > { > > return attr && attr->sched_deadline != 0 && > > (attr->sched_period == 0 || > > - (s64)(attr->sched_period - attr->sched_deadline) >= 0) && > > - (s64)(attr->sched_deadline - attr->sched_runtime ) >= 0 && > > - attr->sched_runtime >= (2 << (DL_SCALE - 1)); > > + (attr->sched_period >= attr->sched_deadline)) && > > + (attr->sched_deadline >= attr->sched_runtime) && > > + attr->sched_runtime >= (1ULL << DL_SCALE) && > > + (attr->sched_deadline < (1ULL << 63) && > > + attr->sched_period < (1ULL << 63)); > > } > > Could we maybe rewrite that function to look less like a ioccc.org > submission? > Right. > static bool > __checkparam_dl(const struct sched_attr *attr) > { > if (!attr) /* possible at all? */ > return false; > I'd say no, removed. > /* runtime <= deadline <= period */ > if (attr->sched_period < attr->sched_deadline || > attr->sched_deadline < attr->sched_runtime) > return false; > > /* > * Since we truncate DL_SCALE bits make sure we're at least that big, > * if runtime > (1 << DL_SCALE), so must the others be per the above > */ > if (attr->sched_runtime <= (1ULL << DL_SCALE)) > return false; > > /* > * Since we use the MSB for wrap-around and sign issues, make > * sure its not set, if period < 2^63, so must the others be. > */ > if (attr->sched_period & (1ULL << 63)) > return false; > > return true; > } > > Did I miss anything? period can be 0, so we have to check also sched_deadline for MSB set. Thanks, - Juri --- >>From e0c44d7614127f8dfbafc08c30681cb8098271e8 Mon Sep 17 00:00:00 2001 From: Juri Lelli Date: Tue, 13 May 2014 10:15:59 +0200 Subject: [PATCH] sched/deadline: restrict user params max value to 2^63 ns Michael Kerrisk noticed that creating SCHED_DEADLINE reservations with certain parameters (e.g, a runtime of something near 2^64 ns) can cause a system freeze for some amount of time. The problem is that in the interface we have u64 sched_runtime; while internally we need to have a signed runtime (to cope with budget overruns) s64 runtime; At the time we setup a new dl_entity we copy the first value in the second. The cast turns out with negative values when sched_runtime is too big, and this causes the scheduler to go crazy right from the start. Moreover, considering how we deal with deadlines wraparound (s64)(a - b) < 0 we also have to restrict acceptable values for sched_{deadline,period}. This patch fixes the thing checking that user parameters are always below 2^63 ns (still large enough for everyone). It also rewrites other conditions that we check, since in __checkparam_dl we don't have to deal with deadline wraparounds and what we have now erroneously fails when the difference between values is too big. Reported-by: Michael Kerrisk Suggested-by: Peter Zijlstra Signed-off-by: Juri Lelli --- kernel/sched/core.c | 37 ++++++++++++++++++++++++++++++------- 1 file changed, 30 insertions(+), 7 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d9d8ece..682a986 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3188,17 +3188,40 @@ __getparam_dl(struct task_struct *p, struct sched_attr *attr) * We ask for the deadline not being zero, and greater or equal * than the runtime, as well as the period of being zero or * greater than deadline. Furthermore, we have to be sure that - * user parameters are above the internal resolution (1us); we - * check sched_runtime only since it is always the smaller one. + * user parameters are above the internal resolution of 1us (we + * check sched_runtime only since it is always the smaller one) and + * below 2^63 ns (we have to check both sched_deadline and + * sched_period, as the latter can be zero). */ static bool __checkparam_dl(const struct sched_attr *attr) { - return attr && attr->sched_deadline != 0 && - (attr->sched_period == 0 || - (s64)(attr->sched_period - attr->sched_deadline) >= 0) && - (s64)(attr->sched_deadline - attr->sched_runtime ) >= 0 && - attr->sched_runtime >= (2 << (DL_SCALE - 1)); + /* deadline != 0 */ + if (attr->sched_deadline == 0) + return false; + + /* + * Since we truncate DL_SCALE bits, make sure we're at least + * that big. + */ + if (attr->sched_runtime < (1ULL << DL_SCALE)) + return false; + + /* + * Since we use the MSB for wrap-around and sign issues, make + * sure it's not set (mind that period can be equal to zero). + */ + if (attr->sched_deadline & (1ULL << 63) || + attr->sched_period & (1ULL << 63)) + return false; + + /* runtime <= deadline <= period (if period != 0) */ + if ((attr->sched_period != 0 && + attr->sched_period < attr->sched_deadline) || + attr->sched_deadline < attr->sched_runtime) + return false; + + return true; } /* -- 1.7.9.5