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 A5B7FC41513 for ; Tue, 15 Aug 2023 06:09:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234904AbjHOGJL (ORCPT ); Tue, 15 Aug 2023 02:09:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50616 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234886AbjHOGHl (ORCPT ); Tue, 15 Aug 2023 02:07:41 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C9F4C1BF6; Mon, 14 Aug 2023 23:06:28 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 858F863B44; Tue, 15 Aug 2023 06:06:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AA0E6C433C9; Tue, 15 Aug 2023 06:06:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692079560; bh=3fF8zkzYbyZlkRIRqbt1UfQ3YQ0+mOdlH5oL0RtWi+E=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=hcpLM5o/fraEgYYD3wmS4wjNcQLAmyKoBzI556KK7xCG+PtOnwMBygUxLwGxZh5HS LtG9e9RmZ4Ry7dsc2wjZqdLq+IF7KZLAARbyS2fFryb2L1kLgxqUB6FU0kO2s8nGCs sE4UFg1mEjrp7sAqT6BnAzVlfHV5E+QSW2Z+Mgv3ofeMEfChMupdkx8p/ggS8HcVqd xSFvIAwfPM/tbH5NZ+eIBG4Aao2S7ce6JZQyBl7o/r6Wut4rRR796cmD9hpHl3yCrz BQfeoofF9b7jf1dQ8YgI5fpFMWihs6rPHksKCEABmz/qIi8xnqGiix8iSYfeR7FuQR /oJQVH4EiAUsA== Received: by mail-ed1-f46.google.com with SMTP id 4fb4d7f45d1cf-5254f9eda36so3242948a12.1; Mon, 14 Aug 2023 23:06:00 -0700 (PDT) X-Gm-Message-State: AOJu0Yxm9tuzp4ybIx0ok4ioB/uUwak6ZqnhSq9Dmzn8gloVDo+FT70y X+0CJ0GM6SoDfda0dpaUguHabaT/gfNjVy5pTdU= X-Google-Smtp-Source: AGHT+IGV7zP9JNYa1B8ETmftWnQz31OFFk6gqfYd+zlEWsCy1iXHcwzckDYd7cEqYfX0WjxSC7Ou6n4fWK+xp7rwM0o= X-Received: by 2002:a05:6402:1b1b:b0:522:216a:28d4 with SMTP id by27-20020a0564021b1b00b00522216a28d4mr9789262edb.7.1692079558803; Mon, 14 Aug 2023 23:05:58 -0700 (PDT) MIME-Version: 1.0 References: <20230814020045.51950-1-chenhuacai@loongson.cn> <20230814020045.51950-2-chenhuacai@loongson.cn> <18b9119c-cbc8-42a1-a313-9154d73c9841@paulmck-laptop> In-Reply-To: <18b9119c-cbc8-42a1-a313-9154d73c9841@paulmck-laptop> From: Huacai Chen Date: Tue, 15 Aug 2023 14:05:46 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH V4 2/2] rcu: Update jiffies in rcu_cpu_stall_reset() To: paulmck@kernel.org Cc: Huacai Chen , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Thomas Gleixner , Ingo Molnar , John Stultz , Stephen Boyd , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Sergey Senozhatsky , rcu@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Binbin Zhou Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Paul, On Tue, Aug 15, 2023 at 12:15=E2=80=AFAM Paul E. McKenney wrote: > > On Mon, Aug 14, 2023 at 10:00:45AM +0800, Huacai Chen wrote: > > The KGDB initial breakpoint gets an rcu stall warning after commit > > a80be428fbc1f1f3bc9ed924 ("rcu: Do not disable GP stall detection in > > rcu_cpu_stall_reset()"). > > > > [ 53.452051] rcu: INFO: rcu_preempt self-detected stall on CPU > > [ 53.487950] rcu: 3-...0: (1 ticks this GP) idle=3D0e2c/1/0x40000= 00000000000 softirq=3D375/375 fqs=3D8 > > [ 53.528243] rcu: (t=3D12297 jiffies g=3D-995 q=3D1 ncpus=3D4) > > [ 53.564840] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc2+ #48= 48 > > [ 53.603005] Hardware name: Loongson Loongson-3A5000-HV-7A2000-1w-V0.= 1-CRB/Loongson-LS3A5000-7A2000-1w-CRB-V1.21, BIOS Loongson-UDK2018-V2.0.050= 99-beta8 08 > > [ 53.682062] pc 9000000000332100 ra 90000000003320f4 tp 90000001000a0= 000 sp 90000001000a3710 > > [ 53.724934] a0 9000000001d4b488 a1 0000000000000000 a2 0000000000000= 001 a3 0000000000000000 > > [ 53.768179] a4 9000000001d526c8 a5 90000001000a38f0 a6 0000000000000= 02c a7 0000000000000000 > > [ 53.810751] t0 00000000000002b0 t1 0000000000000004 t2 900000000131c= 9c0 t3 fffffffffffffffa > > [ 53.853249] t4 0000000000000080 t5 90000001002ac190 t6 0000000000000= 004 t7 9000000001912d58 > > [ 53.895684] t8 0000000000000000 u0 90000000013141a0 s9 0000000000000= 028 s0 9000000001d512f0 > > [ 53.937633] s1 9000000001d51278 s2 90000001000a3798 s3 90000000019fc= 410 s4 9000000001d4b488 > > [ 53.979486] s5 9000000001d512f0 s6 90000000013141a0 s7 0000000000000= 078 s8 9000000001d4b450 > > [ 54.021175] ra: 90000000003320f4 kgdb_cpu_enter+0x534/0x640 > > [ 54.060150] ERA: 9000000000332100 kgdb_cpu_enter+0x540/0x640 > > [ 54.098347] CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=3DCC DACM=3DCC -W= E) > > [ 54.136621] PRMD: 0000000c (PPLV0 +PIE +PWE) > > [ 54.172192] EUEN: 00000000 (-FPE -SXE -ASXE -BTE) > > [ 54.207838] ECFG: 00071c1c (LIE=3D2-4,10-12 VS=3D7) > > [ 54.242503] ESTAT: 00000800 [INT] (IS=3D11 ECode=3D0 EsubCode=3D0) > > [ 54.277996] PRID: 0014c011 (Loongson-64bit, Loongson-3A5000-HV) > > [ 54.313544] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc2+ #48= 48 > > [ 54.430170] Stack : 0072617764726148 0000000000000000 90000000002235= 04 90000001000a0000 > > [ 54.472308] 9000000100073a90 9000000100073a98 00000000000000= 00 9000000100073bd8 > > [ 54.514413] 9000000100073bd0 9000000100073bd0 9000000100073a= 00 0000000000000001 > > [ 54.556018] 0000000000000001 9000000100073a98 99828271f24e96= 1a 90000001002810c0 > > [ 54.596924] 0000000000000001 0000000000010003 00000000000000= 00 0000000000000001 > > [ 54.637115] ffff8000337cdb80 0000000000000001 00000000063600= 00 900000000131c9c0 > > [ 54.677049] 0000000000000000 0000000000000000 90000000017b4c= 98 9000000001912000 > > [ 54.716394] 9000000001912f68 9000000001913000 9000000001912f= 70 00000000000002b0 > > [ 54.754880] 90000000014a8840 0000000000000000 90000000002235= 1c 0000000000000000 > > [ 54.792372] 00000000000002b0 000000000000000c 00000000000000= 00 0000000000071c1c > > [ 54.829302] ... > > [ 54.859163] Call Trace: > > [ 54.859165] [<900000000022351c>] show_stack+0x5c/0x180 > > [ 54.918298] [<90000000012f6100>] dump_stack_lvl+0x60/0x88 > > [ 54.949251] [<90000000012dd5d8>] rcu_dump_cpu_stacks+0xf0/0x148 > > [ 54.981116] [<90000000002d2fb8>] rcu_sched_clock_irq+0xb78/0xe60 > > [ 55.012744] [<90000000002e47cc>] update_process_times+0x6c/0xc0 > > [ 55.044169] [<90000000002f65d4>] tick_sched_timer+0x54/0x100 > > [ 55.075488] [<90000000002e5174>] __hrtimer_run_queues+0x154/0x240 > > [ 55.107347] [<90000000002e6288>] hrtimer_interrupt+0x108/0x2a0 > > [ 55.139112] [<9000000000226418>] constant_timer_interrupt+0x38/0x60 > > [ 55.170749] [<90000000002b3010>] __handle_irq_event_percpu+0x50/0x16= 0 > > [ 55.203141] [<90000000002b3138>] handle_irq_event_percpu+0x18/0x80 > > [ 55.235064] [<90000000002b9d54>] handle_percpu_irq+0x54/0xa0 > > [ 55.266241] [<90000000002b2168>] generic_handle_domain_irq+0x28/0x40 > > [ 55.298466] [<9000000000aba95c>] handle_cpu_irq+0x5c/0xa0 > > [ 55.329749] [<90000000012f7270>] handle_loongarch_irq+0x30/0x60 > > [ 55.361476] [<90000000012f733c>] do_vint+0x9c/0x100 > > [ 55.391737] [<9000000000332100>] kgdb_cpu_enter+0x540/0x640 > > [ 55.422440] [<9000000000332b64>] kgdb_handle_exception+0x104/0x180 > > [ 55.452911] [<9000000000232478>] kgdb_loongarch_notify+0x38/0xa0 > > [ 55.481964] [<900000000026b4d4>] notify_die+0x94/0x100 > > [ 55.509184] [<90000000012f685c>] do_bp+0x21c/0x340 > > [ 55.562475] [<90000000003315b8>] kgdb_compiled_break+0x0/0x28 > > [ 55.590319] [<9000000000332e80>] kgdb_register_io_module+0x160/0x1c0 > > [ 55.618901] [<9000000000c0f514>] configure_kgdboc+0x154/0x1c0 > > [ 55.647034] [<9000000000c0f5e0>] kgdboc_probe+0x60/0x80 > > [ 55.674647] [<9000000000c96da8>] platform_probe+0x68/0x100 > > [ 55.702613] [<9000000000c938e0>] really_probe+0xc0/0x340 > > [ 55.730528] [<9000000000c93be4>] __driver_probe_device+0x84/0x140 > > [ 55.759615] [<9000000000c93cdc>] driver_probe_device+0x3c/0x120 > > [ 55.787990] [<9000000000c93e8c>] __device_attach_driver+0xcc/0x160 > > [ 55.817145] [<9000000000c91290>] bus_for_each_drv+0x90/0x100 > > [ 55.845654] [<9000000000c94328>] __device_attach+0xa8/0x1a0 > > [ 55.874145] [<9000000000c925f0>] bus_probe_device+0xb0/0xe0 > > [ 55.902572] [<9000000000c8ec7c>] device_add+0x65c/0x860 > > [ 55.930635] [<9000000000c96704>] platform_device_add+0x124/0x2c0 > > [ 55.959669] [<9000000001452b38>] init_kgdboc+0x58/0xa0 > > [ 55.987677] [<900000000022015c>] do_one_initcall+0x7c/0x1e0 > > [ 56.016134] [<9000000001420f1c>] kernel_init_freeable+0x22c/0x2a0 > > [ 56.045128] [<90000000012f923c>] kernel_init+0x20/0x124 > > > > Currently rcu_cpu_stall_reset() set rcu_state.jiffies_stall to one chec= k > > period later, i.e. jiffies + rcu_jiffies_till_stall_check(). But jiffie= s > > is only updated in the timer interrupt, so when kgdb_cpu_enter() begins > > to run there may already be nearly one rcu check period after jiffies. > > Since all interrupts are disabled during kgdb_cpu_enter(), jiffies will > > not be updated. When kgdb_cpu_enter() returns, rcu_state.jiffies_stall > > maybe already gets timeout. > > > > We can set rcu_state.jiffies_stall to two rcu check periods later, e.g. > > jiffies + (rcu_jiffies_till_stall_check() * 2) in rcu_cpu_stall_reset() > > to avoid this problem. But this isn't a complete solution because kgdb > > may take a very long time in irq disabled context. > > > > Instead, update jiffies at the beginning of rcu_cpu_stall_reset() can > > solve all kinds of problems. > > Would it make sense for there to be a kgdb_cpu_exit()? In that case, > the stalls could simply be suppressed at the beginning of the debug > session and re-enabled upon exit, as is currently done for sysrq output > via rcu_sysrq_start() and rcu_sysrq_end(). Thank you for your advice, but that doesn't help. Because rcu_sysrq_start() and rcu_sysrq_end() try to suppress the warnings during sysrq, but kgdb already has no warnings during kgdb_cpu_enter() since it is executed in irq disabled context. Instead, this patch wants to suppress the warnings *after* kgdb_cpu_enter() due to a very old jiffies value. Huacai > > Thanx, Paul > > > Cc: stable@vger.kernel.org > > Fixes: a80be428fbc1f1f3bc9ed924 ("rcu: Do not disable GP stall detectio= n in rcu_cpu_stall_reset()") > > Reported-off-by: Binbin Zhou > > Signed-off-by: Huacai Chen > > --- > > kernel/rcu/tree_stall.h | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h > > index b10b8349bb2a..1c7b540985bf 100644 > > --- a/kernel/rcu/tree_stall.h > > +++ b/kernel/rcu/tree_stall.h > > @@ -153,6 +153,7 @@ static void panic_on_rcu_stall(void) > > */ > > void rcu_cpu_stall_reset(void) > > { > > + do_update_jiffies_64(ktime_get()); > > WRITE_ONCE(rcu_state.jiffies_stall, > > jiffies + rcu_jiffies_till_stall_check()); > > } > > -- > > 2.39.3 > >