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[2620:137:e000::1:20]) by mx.google.com with ESMTP id l18-20020a056a00141200b00686ef19c4d2si13387143pfu.325.2023.08.17.08.01.12; Thu, 17 Aug 2023 08:01:28 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=uK5sXJhH; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348720AbjHQIG4 (ORCPT + 99 others); Thu, 17 Aug 2023 04:06:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36510 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348743AbjHQIGd (ORCPT ); Thu, 17 Aug 2023 04:06:33 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5E3962D77; Thu, 17 Aug 2023 01:06:31 -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 E22BE6524A; Thu, 17 Aug 2023 08:06:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2AF7BC433CC; Thu, 17 Aug 2023 08:06:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692259590; bh=pmoGleVhd8MZ73JWrhPmJMhOV2uZdrh3BJkC59h6O3s=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=uK5sXJhHdIiN3KII4z7IY95vt8enLDhsqpIFOIYx0N3xD0lL5t0oEQzLBTUswvkbv B/Z884GSXDMNcFWgtfVvE1RAkE5LL+P/q2ndBYK0Cs2iwJsBXUwT8W5G/DEIn3iMCh cKosDmok1D5ruq7SxKXiVsh60JmBEfOH+wDOEGjvP19AMai+pz60stltyD2lW5lwic Yf3zB4tIcE9iJGgUAII/HUQLPqjNxyokGKIw68v2U0cdwj9SeKYVoZXYNPE4JG1JAp mfUPPC/ur2tVsXJxQEiXDfNTWdmRsSCBM8lAfmAEVrD5cxhyN+eoFMF0bl7ce3oyuz mwJ7W4ZVzESHA== Received: by mail-ed1-f46.google.com with SMTP id 4fb4d7f45d1cf-5254f9eda36so6267266a12.1; Thu, 17 Aug 2023 01:06:30 -0700 (PDT) X-Gm-Message-State: AOJu0YwwrRVrU21ResttOEkUAGjahfAURtHfoSf+/GNdgDZ8urbG6WGZ 8uUg85Ae8/t7dSg1KmrEjSoo4BvLaATWa2cQmyE= X-Received: by 2002:a05:6402:712:b0:523:3ff6:dfc2 with SMTP id w18-20020a056402071200b005233ff6dfc2mr3146353edx.29.1692259588270; Thu, 17 Aug 2023 01:06:28 -0700 (PDT) MIME-Version: 1.0 References: <5777BD82-2C8D-4BAB-BDD3-C2C003DC57FB@joelfernandes.org> In-Reply-To: <5777BD82-2C8D-4BAB-BDD3-C2C003DC57FB@joelfernandes.org> From: Huacai Chen Date: Thu, 17 Aug 2023 16:06:15 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH V4 2/2] rcu: Update jiffies in rcu_cpu_stall_reset() To: Joel Fernandes Cc: Z qiang , paulmck@kernel.org, Huacai Chen , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Boqun Feng , Thomas Gleixner , Ingo Molnar , John Stultz , Stephen Boyd , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , 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 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Joel, On Thu, Aug 17, 2023 at 3:27=E2=80=AFAM Joel Fernandes wrote: > > > > > On Aug 16, 2023, at 8:29 AM, Huacai Chen wrote: > > > > =EF=BB=BFHi, Qiang, > > > >> On Wed, Aug 16, 2023 at 6:06=E2=80=AFPM Z qiang wrote: > >> > >>> > >>> Hi, Qiang, > >>> > >>> On Wed, Aug 16, 2023 at 1:09=E2=80=AFPM Z qiang wrote: > >>>> > >>>>> > >>>>> Hi, Qiang, > >>>>> > >>>>> On Wed, Aug 16, 2023 at 11:16=E2=80=AFAM Z qiang wrote: > >>>>>> > >>>>>>> > >>>>>>> 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 com= mit > >>>>>>>>> a80be428fbc1f1f3bc9ed924 ("rcu: Do not disable GP stall detecti= on in > >>>>>>>>> rcu_cpu_stall_reset()"). > >>>>>>>>> > >>>>>>>>> [ 53.452051] rcu: INFO: rcu_preempt self-detected stall on CP= U > >>>>>>>>> [ 53.487950] rcu: 3-...0: (1 ticks this GP) idle=3D0e2c/1= /0x4000000000000000 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+ #4848 > >>>>>>>>> [ 53.603005] Hardware name: Loongson Loongson-3A5000-HV-7A200= 0-1w-V0.1-CRB/Loongson-LS3A5000-7A2000-1w-CRB-V1.21, BIOS Loongson-UDK2018-= V2.0.05099-beta8 08 > >>>>>>>>> [ 53.682062] pc 9000000000332100 ra 90000000003320f4 tp 90000= 001000a0000 sp 90000001000a3710 > >>>>>>>>> [ 53.724934] a0 9000000001d4b488 a1 0000000000000000 a2 00000= 00000000001 a3 0000000000000000 > >>>>>>>>> [ 53.768179] a4 9000000001d526c8 a5 90000001000a38f0 a6 00000= 0000000002c a7 0000000000000000 > >>>>>>>>> [ 53.810751] t0 00000000000002b0 t1 0000000000000004 t2 90000= 0000131c9c0 t3 fffffffffffffffa > >>>>>>>>> [ 53.853249] t4 0000000000000080 t5 90000001002ac190 t6 00000= 00000000004 t7 9000000001912d58 > >>>>>>>>> [ 53.895684] t8 0000000000000000 u0 90000000013141a0 s9 00000= 00000000028 s0 9000000001d512f0 > >>>>>>>>> [ 53.937633] s1 9000000001d51278 s2 90000001000a3798 s3 90000= 000019fc410 s4 9000000001d4b488 > >>>>>>>>> [ 53.979486] s5 9000000001d512f0 s6 90000000013141a0 s7 00000= 00000000078 s8 9000000001d4b450 > >>>>>>>>> [ 54.021175] ra: 90000000003320f4 kgdb_cpu_enter+0x534/0x6= 40 > >>>>>>>>> [ 54.060150] ERA: 9000000000332100 kgdb_cpu_enter+0x540/0x6= 40 > >>>>>>>>> [ 54.098347] CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=3DCC DACM= =3DCC -WE) > >>>>>>>>> [ 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 EsubCod= e=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+ #4848 > >>>>>>>>> [ 54.430170] Stack : 0072617764726148 0000000000000000 900000= 0000223504 90000001000a0000 > >>>>>>>>> [ 54.472308] 9000000100073a90 9000000100073a98 000000= 0000000000 9000000100073bd8 > >>>>>>>>> [ 54.514413] 9000000100073bd0 9000000100073bd0 900000= 0100073a00 0000000000000001 > >>>>>>>>> [ 54.556018] 0000000000000001 9000000100073a98 998282= 71f24e961a 90000001002810c0 > >>>>>>>>> [ 54.596924] 0000000000000001 0000000000010003 000000= 0000000000 0000000000000001 > >>>>>>>>> [ 54.637115] ffff8000337cdb80 0000000000000001 000000= 0006360000 900000000131c9c0 > >>>>>>>>> [ 54.677049] 0000000000000000 0000000000000000 900000= 00017b4c98 9000000001912000 > >>>>>>>>> [ 54.716394] 9000000001912f68 9000000001913000 900000= 0001912f70 00000000000002b0 > >>>>>>>>> [ 54.754880] 90000000014a8840 0000000000000000 900000= 000022351c 0000000000000000 > >>>>>>>>> [ 54.792372] 00000000000002b0 000000000000000c 000000= 0000000000 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+0xf0/0x= 148 > >>>>>>>>> [ 54.981116] [<90000000002d2fb8>] rcu_sched_clock_irq+0xb78/0= xe60 > >>>>>>>>> [ 55.012744] [<90000000002e47cc>] update_process_times+0x6c/0= xc0 > >>>>>>>>> [ 55.044169] [<90000000002f65d4>] tick_sched_timer+0x54/0x100 > >>>>>>>>> [ 55.075488] [<90000000002e5174>] __hrtimer_run_queues+0x154/= 0x240 > >>>>>>>>> [ 55.107347] [<90000000002e6288>] hrtimer_interrupt+0x108/0x2= a0 > >>>>>>>>> [ 55.139112] [<9000000000226418>] constant_timer_interrupt+0x= 38/0x60 > >>>>>>>>> [ 55.170749] [<90000000002b3010>] __handle_irq_event_percpu+0= x50/0x160 > >>>>>>>>> [ 55.203141] [<90000000002b3138>] handle_irq_event_percpu+0x1= 8/0x80 > >>>>>>>>> [ 55.235064] [<90000000002b9d54>] handle_percpu_irq+0x54/0xa0 > >>>>>>>>> [ 55.266241] [<90000000002b2168>] generic_handle_domain_irq+0= x28/0x40 > >>>>>>>>> [ 55.298466] [<9000000000aba95c>] handle_cpu_irq+0x5c/0xa0 > >>>>>>>>> [ 55.329749] [<90000000012f7270>] handle_loongarch_irq+0x30/0= x60 > >>>>>>>>> [ 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+0x0/0x2= 8 > >>>>>>>>> [ 55.590319] [<9000000000332e80>] kgdb_register_io_module+0x1= 60/0x1c0 > >>>>>>>>> [ 55.618901] [<9000000000c0f514>] configure_kgdboc+0x154/0x1c= 0 > >>>>>>>>> [ 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/0x= 120 > >>>>>>>>> [ 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+0x124/0= x2c0 > >>>>>>>>> [ 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 check > >>>>>>>>> period later, i.e. jiffies + rcu_jiffies_till_stall_check(). Bu= t jiffies > >>>>>>>>> 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 j= iffies. > >>>>>>>>> Since all interrupts are disabled during kgdb_cpu_enter(), jiff= ies will > >>>>>>>>> not be updated. When kgdb_cpu_enter() returns, rcu_state.jiffie= s_stall > >>>>>>>>> maybe already gets timeout. > >>>>>>>>> > >>>>>>>>> We can set rcu_state.jiffies_stall to two rcu check periods lat= er, 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 becau= se 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 de= bug > >>>>>>>> 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 warning= s > >>>>>>> during sysrq, but kgdb already has no warnings during kgdb_cpu_en= ter() > >>>>>>> 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. > >>>>>>> > >>>>>> > >>>>>> Hello, Huacai > >>>>>> > >>>>>> Is it possible to set the rcu_cpu_stall_suppress is true in > >>>>>> dbg_touch_watchdogs() > >>>>>> and reset the rcu_cpu_stall_suppress at the beginning and end of t= he > >>>>>> RCU grace period? > >>>>> This is possible but not the best: 1, kgdb is not the only caller o= f > >>>>> rcu_cpu_stall_reset(); 2, it is difficult to find the "end" to rese= t > >>>>> rcu_cpu_stall_suppress. > >>>>> > >>>> > >>>> You can replace rcu_state.jiffies_stall update by setting rcu_cpu_st= all_suppress > >>>> in rcu_cpu_stall_reset(), and reset rcu_cpu_stall_suppress in rcu_g= p_init() and > >>>> rcu_gp_cleanup(). > >>> What's the advantage compared with updating jiffies? Updating jiffies > >>> seems more straight forward. > >>> > >> > >> In do_update_jiffies_64(), need to acquire jiffies_lock raw spinlock, > >> like you said, kgdb is not the only caller of rcu_cpu_stall_reset(), > >> the rcu_cpu_stall_reset() maybe invoke in NMI (arch/x86/platform/uv/u= v_nmi.c) > > Reset rcu_cpu_stall_suppress in rcu_gp_init()/rcu_gp_cleanup() is > > still not so good to me, because it does a useless operation in most > > cases. Moreover, the rcu core is refactored again and again, something > > may be changed in future. > > > > If do_update_jiffies_64() cannot be used in NMI context, > > Can you not make the jiffies update conditional on whether it is called w= ithin NMI context? > > > can we > > consider my old method [1]? > > https://lore.kernel.org/rcu/CAAhV-H7j9Y=3DVvRLm8thLw-EX1PGqBA9YfT4G1AN7= ucYS=3DiP+DQ@mail.gmail.com/T/#t > > > > Of course we should set rcu_state.jiffies_stall large enough, so we > > can do like this: > > > > void rcu_cpu_stall_reset(void) > > { > > WRITE_ONCE(rcu_state.jiffies_stall, > > - jiffies + rcu_jiffies_till_stall_check()); > > + jiffies + 300 * HZ); > > } > > > > 300s is the largest timeout value, and I think 300s is enough here in p= ractice. > > I dislike that.. Is this acceptable? void rcu_cpu_stall_reset(void) { unsigned long delta; delta =3D nsecs_to_jiffies(ktime_get_ns() - ktime_get_coarse_ns()); WRITE_ONCE(rcu_state.jiffies_stall, jiffies + delta + rcu_jiffies_till_stall_check()); } This can update jiffies_stall without updating jiffies (but has the same effect). Huacai > > Thanks, > > - Joel > > > > > > > Huacai > > > >> > >> Thanks > >> Zqiang > >> > >> > >>> Huacai > >>> > >>>> > >>>> Thanks > >>>> Zqiang > >>>> > >>>>> > >>>>>> or set rcupdate.rcu_cpu_stall_suppress_at_boot=3D1 in bootargs can > >>>>>> suppress RCU stall > >>>>>> in booting. > >>>>> This is also possible, but it suppresses all kinds of stall warning= s, > >>>>> which is not what we want. > >>>>> > >>>>> Huacai > >>>>>> > >>>>>> > >>>>>> Thanks > >>>>>> Zqiang > >>>>>> > >>>>>> > >>>>>>> > >>>>>>> Huacai > >>>>>>> > >>>>>>>> > >>>>>>>> Thanx, Pa= ul > >>>>>>>> > >>>>>>>>> Cc: stable@vger.kernel.org > >>>>>>>>> Fixes: a80be428fbc1f1f3bc9ed924 ("rcu: Do not disable GP stall = detection 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 > >>>>>>>>>