From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 838AAC433EF for ; Thu, 30 Jun 2022 22:37:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230315AbiF3WhR (ORCPT ); Thu, 30 Jun 2022 18:37:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34834 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229563AbiF3WhP (ORCPT ); Thu, 30 Jun 2022 18:37:15 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A12D81EEF4 for ; Thu, 30 Jun 2022 15:37:14 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3BC0C62433 for ; Thu, 30 Jun 2022 22:37:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A1DDC34115; Thu, 30 Jun 2022 22:37:12 +0000 (UTC) Date: Thu, 30 Jun 2022 18:37:04 -0400 From: Steven Rostedt To: Satya Durga Srinivasu Prabhala Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched: fix rq lock recursion issue Message-ID: References: <20220624074240.13108-1-quic_satyap@quicinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220624074240.13108-1-quic_satyap@quicinc.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 24, 2022 at 12:42:40AM -0700, Satya Durga Srinivasu Prabhala wrote: > Below recursion is observed in a rare scenario where __schedule() > takes rq lock, at around same time task's affinity is being changed, > bpf function for tracing sched_switch calls migrate_enabled(), > checks for affinity change (cpus_ptr != cpus_mask) lands into > __set_cpus_allowed_ptr which tries acquire rq lock and causing the > recursion bug. > > Fix the issue by switching to preempt_enable/disable() for non-RT > Kernels. > > -010 |spin_bug(lock = ???, msg = ???) > -011 |debug_spin_lock_before(inline) > -011 |do_raw_spin_lock(lock = 0xFFFFFF89323BB600) > -012 |_raw_spin_lock(inline) > -012 |raw_spin_rq_lock_nested(inline) > -012 |raw_spin_rq_lock(inline) > -012 |task_rq_lock(p = 0xFFFFFF88CFF1DA00, rf = 0xFFFFFFC03707BBE8) > -013 |__set_cpus_allowed_ptr(inline) > -013 |migrate_enable() > -014 |trace_call_bpf(call = ?, ctx = 0xFFFFFFFDEF954600) > -015 |perf_trace_run_bpf_submit(inline) > -015 |perf_trace_sched_switch(__data = 0xFFFFFFE82CF0BCB8, preempt = FALSE, prev = ?, next = ?) > -016 |__traceiter_sched_switch(inline) > -016 |trace_sched_switch(inline) trace_sched_switch() disables preemption. So how is this a fix? -- Steve > -016 |__schedule(sched_mode = ?) > -017 |schedule() > -018 |arch_local_save_flags(inline) > -018 |arch_irqs_disabled(inline) > -018 |__raw_spin_lock_irq(inline) > -018 |_raw_spin_lock_irq(inline) > -018 |worker_thread(__worker = 0xFFFFFF88CE251300) > -019 |kthread(_create = 0xFFFFFF88730A5A80) > -020 |ret_from_fork(asm) > > Signed-off-by: Satya Durga Srinivasu Prabhala > --- > kernel/sched/core.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index bfa7452ca92e..e254e9227341 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2223,6 +2223,7 @@ static void migrate_disable_switch(struct rq *rq, struct task_struct *p) > > void migrate_disable(void) > { > +#ifdef CONFIG_PREEMPT_RT > struct task_struct *p = current; > > if (p->migration_disabled) { > @@ -2234,11 +2235,15 @@ void migrate_disable(void) > this_rq()->nr_pinned++; > p->migration_disabled = 1; > preempt_enable(); > +#else > + preempt_disable(); > +#endif > } > EXPORT_SYMBOL_GPL(migrate_disable); > > void migrate_enable(void) > { > +#ifdef CONFIG_PREEMPT_RT > struct task_struct *p = current; > > if (p->migration_disabled > 1) { > @@ -2265,6 +2270,9 @@ void migrate_enable(void) > p->migration_disabled = 0; > this_rq()->nr_pinned--; > preempt_enable(); > +#else > + preempt_enable(); > +#endif > } > EXPORT_SYMBOL_GPL(migrate_enable); > > -- > 2.36.1