From patchwork Tue Apr 5 01:07:51 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Frederic Weisbecker X-Patchwork-Id: 558483 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 9CF4BC433EF for ; Tue, 5 Apr 2022 01:59:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229580AbiDECBk (ORCPT ); Mon, 4 Apr 2022 22:01:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38412 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229546AbiDECBj (ORCPT ); Mon, 4 Apr 2022 22:01:39 -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 EF48C462B01; Mon, 4 Apr 2022 18:18:12 -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 30A9060DC6; Tue, 5 Apr 2022 01:08:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 31008C2BBE4; Tue, 5 Apr 2022 01:08:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1649120887; bh=Jpz+Jv4Xaf7lFDh2SyosScKUc58hWmkQlsew08yht+o=; h=From:To:Cc:Subject:Date:From; b=gXub8KIAxJdu63/6MTrPAGneJXnd33dv3jqT5/0InvZyfMvDdsjypiJF0mto6q6Cv YWCf8Tb872r+2Rl4K9dpQUcB0YJk+XoyfGUjkRiSq1wT7U65peaU4UbicSrtviTo8W bKrnRxxCVyVNqiaycQ0H+MvUz/I08bwaZjFP+K+YB68g0lBYcBZPCap2uO3Um6Rr1H 31i+hM6JhR63/nOoS0nS25pbmjnnod8+BTvHDo0btkMBCDBxLEzm+X8BmKfzrn5mVr hP8iJuyoWGAAyVcn2uyRCX0dpaOgNLWjJX73pEa9FAxZ6EIuT9Gx0YdUddFU/a11Oz lO9XgGO2Tr/5Q== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , linux-rt-users , Mel Gorman , Sebastian Andrzej Siewior , Thomas Gleixner Subject: [RT][PATCH 1/2] rcutorture: Also force sched priority to timersd on boosting test Date: Tue, 5 Apr 2022 03:07:51 +0200 Message-Id: <20220405010752.1347437-1-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org ksoftirqd is statically boosted to the priority level right above the one of rcu_torture_boost() so that timers, which torture readers rely on, get a chance to run while rcu_torture_boost() is polling. However timers processing got split from ksoftirqd into their own kthread (timersd) that isn't boosted. It has the same SCHED_FIFO low prio as rcu_torture_boost() and therefore timers can't preempt it and may starve. The issue can be triggered in practice on v5.17.1-rt17 using: ./kvm.sh --allcpus --configs TREE04 --duration 10m --kconfig "CONFIG_EXPERT=y CONFIG_PREEMPT_RT=y" triggering the following: rcu-torture: rcu_torture_boost boosting failed Boost inversion thread ->rt_priority 1 gp_state 12908 jiffies 3501 rcu: rcu_preempt: wait state: RCU_GP_WAIT_FQS(5) ->state: 0x402 ->rt_priority 2 delta ->gp_start 3502 ->gp_activity 3502 ->gp_req_activity 3502 ->gp_wake_time 3502 ->gp_wake_seq 12897 ->gp_seq 12901 ->gp_seq_needed 12904 ->gp_max 4057 ->gp_flags 0x0 rcu: rcu_node 0:7 ->gp_seq 12901 ->gp_seq_needed 12904 ->qsmask 0x2 .... ->n_boosts 0 rcu: rcu_node 0:3 ->gp_seq 12901 ->gp_seq_needed 12908 ->qsmask 0x0 b... ->n_boosts 22 rcu: cpu 0 ->gp_seq_needed 12904 rcu: rcu_node 4:7 ->gp_seq 12901 ->gp_seq_needed 12908 ->qsmask 0x0 b..G ->n_boosts 6 rcu: cpu 5 ->gp_seq_needed 12904 rcu: CB 1^0->2 KbclSW F5089 L5089 C1 ..... q0 S CPU 0 rcu: CB 2^0->3 KbclSW F16859 L16859 C1 ..... q0 S CPU 0 rcu: CB 3^0->-1 KbclSW F3502 L3502 C2 .W12908.N. q4 S CPU 0 rcu: nocb GP 4 KldtS .[W.] .G:12904 rnp 4:7 1459 S CPU 0 rcu: CB 4^4->5 KbclSW F9918 L10534 C4 ..... q0 S CPU 0 rcu: CB 5^4->6 KbclSW F2550 L2550 C2 .W12904.N. q8 S CPU 0 rcu: CB 6^4->7 KbclSW F6639 L7253 C0 ..... q0 S CPU 0 rcu: CB 7^4->-1 KbclSW F30685 L30685 C1 ..... q0 S CPU 0 rcu: RCU callbacks invoked since boot: 236075 rcu_tasks: RTGS_WAIT_CBS(11) since 409853 g:0 i:0/0 k. rcu_tasks_rude: RTGS_WAIT_CBS(11) since 409851 g:0 i:0/0 k. rcu_tasks_trace: RTGS_WAIT_CBS(11) since 409848 g:0 i:0/0 k. N0 h:0/0/0 Boost inversion: GP 12908 still pending. rcu-torture: rtc: 0000000093327eb2 ver: 1504 tfle: 0 rta: 1505 rtaf: 0 rtf: 1493 rtmbe: 0 rtmbkf: 0/782 rtbe: 0 rtbke: 0 rtbre: 0 rtbf: 1 rtb: 7 nt: 66220 onoff: 6/6:11/12 40,763:29,5050 1537:11766 (HZ=1000) barrier: 239/240:0 read-exits: 67 nocb-toggles: 0:0 rcu-torture: !!! ------------[ cut here ]------------ WARNING: CPU: 5 PID: 121 at kernel/rcu/rcutorture.c:1870 rcu_torture_stats_print+0x5ad/0x610 Modules linked in: CPU: 5 PID: 121 Comm: rcu_torture_sta Not tainted 5.17.1-rt17 #63 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009) RIP: 0010:rcu_torture_stats_print+0x5ad/0x610 Code: c7 01 02 00 74 02 0f 0b 48 83 3d 35 c7 01 02 00 74 02 0f 0b 48 83 3d 21 c7 01 02 00 74 02 0f 0b 48 83 3d 0d c7 01 02 00 74 02 <0f> 0b 83 eb 01 0f 8e ba fc ff ff 0f 0b e9 b3 fc ff ff 8b 05 8f c6 RSP: 0018:ffffa7560041fdf8 EFLAGS: 00010202 RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000001 RDX: 0000000000000000 RSI: 40000000ffffe735 RDI: 00000000ffffffff RBP: 00000000000005d5 R08: ffffffffaf65f6e0 R09: ffffffffafee3a7c R10: ffffa75600427d58 R11: 0000000020212121 R12: ffffa7560041fe20 R13: ffffa7560041fe78 R14: 0000000000000000 R15: 000000000001bd20 FS: 0000000000000000(0000) GS:ffff9fe7df540000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 0000000014216000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: ? lock_timer_base+0x62/0x80 ? rcu_torture_stats_print+0x610/0x610 rcu_torture_stats+0x29/0x70 kthread+0x118/0x130 ? kthread_complete_and_exit+0x20/0x20 ret_from_fork+0x22/0x30 Fix this with statically boosting timersd just like is done with ksoftirqd. Suggested-by: Mel Gorman Cc: Sebastian Andrzej Siewior Cc: Thomas Gleixner Signed-off-by: Frederic Weisbecker --- include/linux/interrupt.h | 1 + kernel/rcu/rcutorture.c | 6 ++++++ kernel/softirq.c | 2 +- 3 files changed, 8 insertions(+), 1 deletion(-) diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index db4a23d07a57..e4b8a04e67ce 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -606,6 +606,7 @@ extern void raise_softirq_irqoff(unsigned int nr); extern void raise_softirq(unsigned int nr); #ifdef CONFIG_PREEMPT_RT +DECLARE_PER_CPU(struct task_struct *, timersd); extern void raise_timer_softirq(void); extern void raise_hrtimer_softirq(void); diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 422f7e4cc08d..ac9715ed58ba 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -3283,6 +3283,12 @@ rcu_torture_init(void) WARN_ON_ONCE(!t); sp.sched_priority = 2; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); +#ifdef CONFIG_PREEMPT_RT + t = per_cpu(timersd, cpu); + WARN_ON_ONCE(!t); + sp.sched_priority = 2; + sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); +#endif } } } diff --git a/kernel/softirq.c b/kernel/softirq.c index 22948c2109f5..89eb45614af6 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -624,7 +624,7 @@ static inline void tick_irq_exit(void) #endif } -static DEFINE_PER_CPU(struct task_struct *, timersd); +DEFINE_PER_CPU(struct task_struct *, timersd); static DEFINE_PER_CPU(unsigned long, pending_timer_softirq); static unsigned int local_pending_timers(void)