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 B4372C04FE0 for ; Wed, 16 Aug 2023 12:30:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245241AbjHPM3h (ORCPT ); Wed, 16 Aug 2023 08:29:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60358 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245253AbjHPM3I (ORCPT ); Wed, 16 Aug 2023 08:29:08 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 144152705; Wed, 16 Aug 2023 05:29:04 -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 97E936682D; Wed, 16 Aug 2023 12:29:03 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D9D88C433CC; Wed, 16 Aug 2023 12:29:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692188943; bh=JfECNxQFNHmkFIgs6SUzhiwAem2MAlpAOG6ZY2xyhOE=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=JKUXUuysJoxlrIKQlKan2MIGLQtCJOOQPTNCanNSL3JR9VfFHEHuM5Pm1Cc3byjY1 mx3m6/j7VWwrGdI4LrGb0PltB1rPho64yisi3/FMghyw7SneipH2teGhAgNI3v2hP9 hPpZ25x1PgaOhvBeBiXFPTiDok1J6yvjayk/dfggnObkBjW+CjAVc/hIeYRKLNxM+x JTIBgTZSnChI2uj1tMKwvWSI/2S9pN0c1Jjyk6sUE0Wn7k8dY6RQfXvKXZ/Gjwi/rT rK5wUYeuJOF/eqGfiMOfAmNlPSp88Emh4Kx/QCXTinoOU8GJHX7pt2cqWbnTVQPtm4 gIrvqqRLt3RpA== Received: by mail-lf1-f54.google.com with SMTP id 2adb3069b0e04-4ff933f9ca8so699352e87.1; Wed, 16 Aug 2023 05:29:02 -0700 (PDT) X-Gm-Message-State: AOJu0Ywg05O6esWfNgUAi4AsBqyG754aZvgG7PKzxcwQmBuEJ/wMGvtt i5ksYxp9BFMiqRuGMEoDBgPves+l6qH/gVGQacQ= X-Google-Smtp-Source: AGHT+IG7E4dOZ48hLxFd4z1+z9MS2KpKJ1nepP+SsvTY1SfniU34522QriVlzbGV1N6spMSyz0mKoo6Uzqwvc8qvw44= X-Received: by 2002:a05:6512:10c6:b0:4fe:1c40:9274 with SMTP id k6-20020a05651210c600b004fe1c409274mr1880220lfg.41.1692188940768; Wed, 16 Aug 2023 05:29:00 -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: From: Huacai Chen Date: Wed, 16 Aug 2023 20:28:54 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH V4 2/2] rcu: Update jiffies in rcu_cpu_stall_reset() To: Z qiang Cc: paulmck@kernel.org, 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 , 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, 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= commit > > > > > > > > a80be428fbc1f1f3bc9ed924 ("rcu: Do not disable GP stall det= ection in > > > > > > > > rcu_cpu_stall_reset()"). > > > > > > > > > > > > > > > > [ 53.452051] rcu: INFO: rcu_preempt self-detected stall o= n CPU > > > > > > > > [ 53.487950] rcu: 3-...0: (1 ticks this GP) idle=3D0e= 2c/1/0x4000000000000000 softirq=3D375/375 fqs=3D8 > > > > > > > > [ 53.528243] rcu: (t=3D12297 jiffies g=3D-995 q=3D1 n= cpus=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-7= A2000-1w-V0.1-CRB/Loongson-LS3A5000-7A2000-1w-CRB-V1.21, BIOS Loongson-UDK2= 018-V2.0.05099-beta8 08 > > > > > > > > [ 53.682062] pc 9000000000332100 ra 90000000003320f4 tp 9= 0000001000a0000 sp 90000001000a3710 > > > > > > > > [ 53.724934] a0 9000000001d4b488 a1 0000000000000000 a2 0= 000000000000001 a3 0000000000000000 > > > > > > > > [ 53.768179] a4 9000000001d526c8 a5 90000001000a38f0 a6 0= 00000000000002c a7 0000000000000000 > > > > > > > > [ 53.810751] t0 00000000000002b0 t1 0000000000000004 t2 9= 00000000131c9c0 t3 fffffffffffffffa > > > > > > > > [ 53.853249] t4 0000000000000080 t5 90000001002ac190 t6 0= 000000000000004 t7 9000000001912d58 > > > > > > > > [ 53.895684] t8 0000000000000000 u0 90000000013141a0 s9 0= 000000000000028 s0 9000000001d512f0 > > > > > > > > [ 53.937633] s1 9000000001d51278 s2 90000001000a3798 s3 9= 0000000019fc410 s4 9000000001d4b488 > > > > > > > > [ 53.979486] s5 9000000001d512f0 s6 90000000013141a0 s7 0= 000000000000078 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 -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 Esu= bCode=3D0) > > > > > > > > [ 54.277996] PRID: 0014c011 (Loongson-64bit, Loongson-3A= 5000-HV) > > > > > > > > [ 54.313544] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 6.= 5.0-rc2+ #4848 > > > > > > > > [ 54.430170] Stack : 0072617764726148 0000000000000000 90= 00000000223504 90000001000a0000 > > > > > > > > [ 54.472308] 9000000100073a90 9000000100073a98 00= 00000000000000 9000000100073bd8 > > > > > > > > [ 54.514413] 9000000100073bd0 9000000100073bd0 90= 00000100073a00 0000000000000001 > > > > > > > > [ 54.556018] 0000000000000001 9000000100073a98 99= 828271f24e961a 90000001002810c0 > > > > > > > > [ 54.596924] 0000000000000001 0000000000010003 00= 00000000000000 0000000000000001 > > > > > > > > [ 54.637115] ffff8000337cdb80 0000000000000001 00= 00000006360000 900000000131c9c0 > > > > > > > > [ 54.677049] 0000000000000000 0000000000000000 90= 000000017b4c98 9000000001912000 > > > > > > > > [ 54.716394] 9000000001912f68 9000000001913000 90= 00000001912f70 00000000000002b0 > > > > > > > > [ 54.754880] 90000000014a8840 0000000000000000 90= 0000000022351c 0000000000000000 > > > > > > > > [ 54.792372] 00000000000002b0 000000000000000c 00= 00000000000000 0000000000071c1c > > > > > > > > [ 54.829302] ... > > > > > > > > [ 54.859163] Call Trace: > > > > > > > > [ 54.859165] [<900000000022351c>] show_stack+0x5c/0x180 > > > > > > > > [ 54.918298] [<90000000012f6100>] dump_stack_lvl+0x60/0x8= 8 > > > > > > > > [ 54.949251] [<90000000012dd5d8>] rcu_dump_cpu_stacks+0xf= 0/0x148 > > > > > > > > [ 54.981116] [<90000000002d2fb8>] rcu_sched_clock_irq+0xb= 78/0xe60 > > > > > > > > [ 55.012744] [<90000000002e47cc>] update_process_times+0x= 6c/0xc0 > > > > > > > > [ 55.044169] [<90000000002f65d4>] tick_sched_timer+0x54/0= x100 > > > > > > > > [ 55.075488] [<90000000002e5174>] __hrtimer_run_queues+0x= 154/0x240 > > > > > > > > [ 55.107347] [<90000000002e6288>] hrtimer_interrupt+0x108= /0x2a0 > > > > > > > > [ 55.139112] [<9000000000226418>] constant_timer_interrup= t+0x38/0x60 > > > > > > > > [ 55.170749] [<90000000002b3010>] __handle_irq_event_perc= pu+0x50/0x160 > > > > > > > > [ 55.203141] [<90000000002b3138>] handle_irq_event_percpu= +0x18/0x80 > > > > > > > > [ 55.235064] [<90000000002b9d54>] handle_percpu_irq+0x54/= 0xa0 > > > > > > > > [ 55.266241] [<90000000002b2168>] generic_handle_domain_i= rq+0x28/0x40 > > > > > > > > [ 55.298466] [<9000000000aba95c>] handle_cpu_irq+0x5c/0xa= 0 > > > > > > > > [ 55.329749] [<90000000012f7270>] handle_loongarch_irq+0x= 30/0x60 > > > > > > > > [ 55.361476] [<90000000012f733c>] do_vint+0x9c/0x100 > > > > > > > > [ 55.391737] [<9000000000332100>] kgdb_cpu_enter+0x540/0x= 640 > > > > > > > > [ 55.422440] [<9000000000332b64>] kgdb_handle_exception+0= x104/0x180 > > > > > > > > [ 55.452911] [<9000000000232478>] kgdb_loongarch_notify+0= x38/0xa0 > > > > > > > > [ 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+0x68/0x1= 00 > > > > > > > > [ 55.702613] [<9000000000c938e0>] really_probe+0xc0/0x340 > > > > > > > > [ 55.730528] [<9000000000c93be4>] __driver_probe_device+0= x84/0x140 > > > > > > > > [ 55.759615] [<9000000000c93cdc>] driver_probe_device+0x3= c/0x120 > > > > > > > > [ 55.787990] [<9000000000c93e8c>] __device_attach_driver+= 0xcc/0x160 > > > > > > > > [ 55.817145] [<9000000000c91290>] bus_for_each_drv+0x90/0= x100 > > > > > > > > [ 55.845654] [<9000000000c94328>] __device_attach+0xa8/0x= 1a0 > > > > > > > > [ 55.874145] [<9000000000c925f0>] bus_probe_device+0xb0/0= xe0 > > > > > > > > [ 55.902572] [<9000000000c8ec7c>] device_add+0x65c/0x860 > > > > > > > > [ 55.930635] [<9000000000c96704>] platform_device_add+0x1= 24/0x2c0 > > > > > > > > [ 55.959669] [<9000000001452b38>] init_kgdboc+0x58/0xa0 > > > > > > > > [ 55.987677] [<900000000022015c>] do_one_initcall+0x7c/0x= 1e0 > > > > > > > > [ 56.016134] [<9000000001420f1c>] kernel_init_freeable+0x= 22c/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()= . But jiffies > > > > > > > > is only updated in the timer interrupt, so when kgdb_cpu_en= ter() begins > > > > > > > > to run there may already be nearly one rcu check period aft= er jiffies. > > > > > > > > Since all interrupts are disabled during kgdb_cpu_enter(), = jiffies will > > > > > > > > not be updated. When kgdb_cpu_enter() returns, rcu_state.ji= ffies_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_s= tall_reset() > > > > > > > > to avoid this problem. But this isn't a complete solution b= ecause kgdb > > > > > > > > may take a very long time in irq disabled context. > > > > > > > > > > > > > > > > Instead, update jiffies at the beginning of rcu_cpu_stall_r= eset() can > > > > > > > > solve all kinds of problems. > > > > > > > > > > > > > > Would it make sense for there to be a kgdb_cpu_exit()? In th= at case, > > > > > > > the stalls could simply be suppressed at the beginning of the= debug > > > > > > > session and re-enabled upon exit, as is currently done for sy= srq 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 warni= ngs > > > > > > during sysrq, but kgdb already has no warnings during kgdb_cpu_= enter() > > > > > > since it is executed in irq disabled context. Instead, this pat= ch > > > > > > 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 = the > > > > > 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_sta= ll_suppress > > > in rcu_cpu_stall_reset(), and reset rcu_cpu_stall_suppress in rcu_gp= _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/uv_n= mi.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 we consider my old method [1]? https://lore.kernel.org/rcu/CAAhV-H7j9Y=3DVvRLm8thLw-EX1PGqBA9YfT4G1AN7ucYS= =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 pract= ice. Huacai > > Thanks > Zqiang > > > > Huacai > > > > > > > > Thanks > > > Zqiang > > > > > > > > > > > > or set rcupdate.rcu_cpu_stall_suppress_at_boot=3D1 in bootargs ca= n > > > > > 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= , Paul > > > > > > > > > > > > > > > Cc: stable@vger.kernel.org > > > > > > > > Fixes: a80be428fbc1f1f3bc9ed924 ("rcu: Do not disable GP st= all 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_stal= l.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 > > > > > > > >