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 D8377C43334 for ; Wed, 6 Jul 2022 03:50:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231493AbiGFDuU (ORCPT ); Tue, 5 Jul 2022 23:50:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49658 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231801AbiGFDty (ORCPT ); Tue, 5 Jul 2022 23:49:54 -0400 Received: from alexa-out-sd-02.qualcomm.com (alexa-out-sd-02.qualcomm.com [199.106.114.39]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6C502205DB for ; Tue, 5 Jul 2022 20:48:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1657079288; x=1688615288; h=subject:to:cc:references:from:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=FtAQ47kRhcsSDlE6KTDwkolcwd+jvA+etT4YjBKsmM0=; b=i52ws6+aDrB9+XkNaAFnhw3IruZXZnF7auoqvUgUiyOdfb4b9fOLY6Pm wjowZJyz7GpwHNyNVu9KMLv8oh1/GA4gY1j4zWK3oykMiW9yqqy6W4Q+Q 4GHcKUL3jhuJeG6Gjwr15zfeR/dChDQaY8QSIb3UAJM1K3TwjfHz77krC U=; Received: from unknown (HELO ironmsg01-sd.qualcomm.com) ([10.53.140.141]) by alexa-out-sd-02.qualcomm.com with ESMTP; 05 Jul 2022 20:48:08 -0700 X-QCInternal: smtphost Received: from nasanex01c.na.qualcomm.com ([10.47.97.222]) by ironmsg01-sd.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Jul 2022 20:48:07 -0700 Received: from nalasex01a.na.qualcomm.com (10.47.209.196) by nasanex01c.na.qualcomm.com (10.47.97.222) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.22; Tue, 5 Jul 2022 20:47:33 -0700 Received: from [10.47.234.156] (10.49.16.6) by nalasex01a.na.qualcomm.com (10.47.209.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.22; Tue, 5 Jul 2022 20:47:33 -0700 Subject: Re: [PATCH] sched: fix rq lock recursion issue To: Steven Rostedt CC: , , , , , , , , , References: <20220624074240.13108-1-quic_satyap@quicinc.com> From: Satya Durga Srinivasu Prabhala Message-ID: <037be4d3-0474-ba9f-fd0f-4bd9af3e835d@quicinc.com> Date: Tue, 5 Jul 2022 20:47:33 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Originating-IP: [10.49.16.6] X-ClientProxiedBy: nalasex01b.na.qualcomm.com (10.47.209.197) To nalasex01a.na.qualcomm.com (10.47.209.196) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/30/22 3:37 PM, Steven Rostedt wrote: > 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? Thanks for your time and comments. I was more looking at non-RT Kernel where switching to preempt_disable/enable() helps as it's just increment/decrement of count. I agree, this isn't a right fix. I'm still cross checking on easy way to repro the issue. Will cross check further and get back. > > -- 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