Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758009Ab1EZRVe (ORCPT ); Thu, 26 May 2011 13:21:34 -0400 Received: from casper.infradead.org ([85.118.1.10]:58269 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757582Ab1EZRVd (ORCPT ); Thu, 26 May 2011 13:21:33 -0400 Subject: Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM From: Peter Zijlstra To: Oleg Nesterov Cc: Marc Zyngier , Yong Zhang , Ingo Molnar , Frank Rowand , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org In-Reply-To: <1306430264.2497.88.camel@laptop> References: <1306343335.21578.65.camel@twins> <1306358128.21578.107.camel@twins> <1306405979.1200.63.camel@twins> <1306407759.27474.207.camel@e102391-lin.cambridge.arm.com> <1306409575.1200.71.camel@twins> <1306412511.1200.90.camel@twins> <20110526154508.GA13788@redhat.com> <1306425584.2497.81.camel@laptop> <1306426148.2497.83.camel@laptop> <20110526170422.GA18413@redhat.com> <1306430264.2497.88.camel@laptop> Content-Type: text/plain; charset="UTF-8" Date: Thu, 26 May 2011 19:23:53 +0200 Message-ID: <1306430633.2497.91.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3205 Lines: 96 On Thu, 2011-05-26 at 19:17 +0200, Peter Zijlstra wrote: > On Thu, 2011-05-26 at 19:04 +0200, Oleg Nesterov wrote: > > On 05/26, Peter Zijlstra wrote: > > > > > > @@ -2636,7 +2636,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > > > * to spin on ->on_cpu if p is current, since that would > > > * deadlock. > > > */ > > > - if (p == current) { > > > + if (cpu == smp_processor_id()) { > > > + p->sched_contributes_to_load = 0; > > > ttwu_queue(p, cpu); > > > > Btw. I do not pretend I really understand se->vruntime, but in this > > case we are doing enqueue_task() without ->task_waking(), however we > > pass ENQUEUE_WAKING. Is it correct? > > No its not, that's the thing that I got wrong the first time and caused > these pauses. We'd end up with something like the below, which isn't too different from what I've now got queued. It has the extra cpu == smp_processor_id() check, but I'm not sure this whole case is worth the trouble. I could go stick some counters in to verify how often all this happens I guess. --- arch/x86/include/asm/system.h | 2 ++ kernel/sched.c | 14 +++++++++++--- kernel/sched_debug.c | 7 +++++++ 3 files changed, 20 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h index c2ff2a1..2c597e8 100644 --- a/arch/x86/include/asm/system.h +++ b/arch/x86/include/asm/system.h @@ -10,6 +10,8 @@ #include #include +#define __ARCH_WANT_INTERRUPTS_ON_CTXSW + /* entries in ARCH_DLINFO: */ #if defined(CONFIG_IA32_EMULATION) || !defined(CONFIG_X86_64) # define AT_VECTOR_SIZE_ARCH 2 diff --git a/kernel/sched.c b/kernel/sched.c index 2d12893..e4f7a9f 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2636,9 +2636,17 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) * to spin on ->on_cpu if p is current, since that would * deadlock. */ - if (p == current) { - ttwu_queue(p, cpu); - goto stat; + if (cpu == smp_processor_id()) { + struct rq *rq; + + rq = __task_rq_lock(p); + if (p->on_cpu) { + ttwu_activate(rq, p, ENQUEUE_WAKEUP); + ttwu_do_wakeup(rq, p, wake_flags); + __task_rq_unlock(rq); + goto stat; + } + __task_rq_unlock(rq); } #endif cpu_relax(); diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c index a6710a1..f0ff1de 100644 --- a/kernel/sched_debug.c +++ b/kernel/sched_debug.c @@ -332,6 +332,13 @@ static int sched_debug_show(struct seq_file *m, void *v) (int)strcspn(init_utsname()->version, " "), init_utsname()->version); +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW + SEQ_printf(m, "__ARCH_WANT_INTERRUPTS_ON_CTXSW\n"); +#endif +#ifdef __ARCH_WANT_UNLOCKED_CTXSW + SEQ_printf(m, "__ARCH_WANT_UNLOCKED_CTXSW\n"); +#endif + #define P(x) \ SEQ_printf(m, "%-40s: %Ld\n", #x, (long long)(x)) #define PN(x) \ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/