Message-ID: <Y8WCWAuQSHN651dA@FVFF77S0Q05N.cambridge.arm.com>
Date:   Mon, 16 Jan 2023 16:59:04 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     richard.henderson@...aro.org, ink@...assic.park.msu.ru,
        mattst88@...il.com, vgupta@...nel.org, linux@...linux.org.uk,
        nsekhar@...com, brgl@...ev.pl, ulli.kroll@...glemail.com,
        linus.walleij@...aro.org, shawnguo@...nel.org,
        Sascha Hauer <s.hauer@...gutronix.de>, kernel@...gutronix.de,
        festevam@...il.com, linux-imx@....com, tony@...mide.com,
        khilman@...nel.org, krzysztof.kozlowski@...aro.org,
        alim.akhtar@...sung.com, catalin.marinas@....com, will@...nel.org,
        guoren@...nel.org, bcain@...cinc.com, chenhuacai@...nel.org,
        kernel@...0n.name, geert@...ux-m68k.org, sammy@...my.net,
        monstr@...str.eu, tsbogend@...ha.franken.de, dinguyen@...nel.org,
        jonas@...thpole.se, stefan.kristiansson@...nalahti.fi,
        shorne@...il.com, James.Bottomley@...senPartnership.com,
        deller@....de, mpe@...erman.id.au, npiggin@...il.com,
        christophe.leroy@...roup.eu, paul.walmsley@...ive.com,
        palmer@...belt.com, aou@...s.berkeley.edu, hca@...ux.ibm.com,
        gor@...ux.ibm.com, agordeev@...ux.ibm.com,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com,
        ysato@...rs.sourceforge.jp, dalias@...c.org, davem@...emloft.net,
        richard@....at, anton.ivanov@...bridgegreys.com,
        johannes@...solutions.net, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, namhyung@...nel.org, jgross@...e.com,
        srivatsa@...il.mit.edu, amakhalov@...are.com,
        pv-drivers@...are.com, boris.ostrovsky@...cle.com,
        chris@...kel.net, jcmvbkbc@...il.com, rafael@...nel.org,
        lenb@...nel.org, pavel@....cz, gregkh@...uxfoundation.org,
        mturquette@...libre.com, sboyd@...nel.org,
        daniel.lezcano@...aro.org, lpieralisi@...nel.org,
        sudeep.holla@....com, agross@...nel.org, andersson@...nel.org,
        konrad.dybcio@...aro.org, anup@...infault.org,
        thierry.reding@...il.com, jonathanh@...dia.com,
        jacob.jun.pan@...ux.intel.com, atishp@...shpatra.org,
        Arnd Bergmann <arnd@...db.de>, yury.norov@...il.com,
        andriy.shevchenko@...ux.intel.com, linux@...musvillemoes.dk,
        dennis@...nel.org, tj@...nel.org, cl@...ux.com,
        rostedt@...dmis.org, mhiramat@...nel.org, frederic@...nel.org,
        paulmck@...nel.org, pmladek@...e.com, senozhatsky@...omium.org,
        john.ogness@...utronix.de, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, ryabinin.a.a@...il.com, glider@...gle.com,
        andreyknvl@...il.com, dvyukov@...gle.com,
        vincenzo.frascino@....com,
        Andrew Morton <akpm@...ux-foundation.org>, jpoimboe@...nel.org,
        linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org, linux-csky@...r.kernel.org,
        linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-perf-users@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-xtensa@...ux-xtensa.org, linux-acpi@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-trace-kernel@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH v3 00/51] cpuidle,rcu: Clean up the mess

On Thu, Jan 12, 2023 at 08:43:14PM +0100, Peter Zijlstra wrote:
> Hi All!

Hi Peter,

> The (hopefully) final respin of cpuidle vs rcu cleanup patches. Barring any
> objections I'll be queueing these patches in tip/sched/core in the next few
> days.

I'm sorry to have to bear some bad news on that front. :(

I just had a go at testing this on a Juno dev board, using your queue.git
sched/idle branch and defconfig + CONFIG_PROVE_LOCKING=y +
CONFIG_DEBUG_LOCKDEP=y + CONFIG_DEBUG_ATOMIC_SLEEP=y.

With that I consistently see RCU at boot time (log below).

| =============================
| WARNING: suspicious RCU usage
| 6.2.0-rc3-00051-gced9b6eecb31 #1 Not tainted
| -----------------------------
| include/trace/events/ipi.h:19 suspicious rcu_dereference_check() usage!
| 
| other info that might help us debug this:
| 
| 
| rcu_scheduler_active = 2, debug_locks = 1
| RCU used illegally from extended quiescent state!
| no locks held by swapper/0/0.
| 
| stack backtrace:
| CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.2.0-rc3-00051-gced9b6eecb31 #1
| Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II May 16 2021
| Call trace:
|  dump_backtrace.part.0+0xe4/0xf0
|  show_stack+0x18/0x30
|  dump_stack_lvl+0x98/0xd4
|  dump_stack+0x18/0x34
|  lockdep_rcu_suspicious+0xf8/0x10c
|  trace_ipi_raise+0x1a8/0x1b0
|  arch_irq_work_raise+0x4c/0x70
|  __irq_work_queue_local+0x48/0x80
|  irq_work_queue+0x50/0x80
|  __wake_up_klogd.part.0+0x98/0xe0
|  defer_console_output+0x20/0x30
|  vprintk+0x98/0xf0
|  _printk+0x5c/0x84
|  lockdep_rcu_suspicious+0x34/0x10c
|  trace_lock_acquire+0x174/0x180
|  lock_acquire+0x3c/0x8c
|  _raw_spin_lock_irqsave+0x70/0x150
|  down_trylock+0x18/0x50
|  __down_trylock_console_sem+0x3c/0xd0
|  console_trylock+0x28/0x90
|  vprintk_emit+0x11c/0x354
|  vprintk_default+0x38/0x4c
|  vprintk+0xd4/0xf0
|  _printk+0x5c/0x84
|  lockdep_rcu_suspicious+0x34/0x10c
|  printk_sprint+0x238/0x240
|  vprintk_store+0x32c/0x4b0
|  vprintk_emit+0x104/0x354
|  vprintk_default+0x38/0x4c
|  vprintk+0xd4/0xf0
|  _printk+0x5c/0x84
|  lockdep_rcu_suspicious+0x34/0x10c
|  trace_irq_disable+0x1ac/0x1b0
|  trace_hardirqs_off+0xe8/0x110
|  cpu_suspend+0x4c/0xfc
|  psci_cpu_suspend_enter+0x58/0x6c
|  psci_enter_idle_state+0x70/0x170
|  cpuidle_enter_state+0xc4/0x464
|  cpuidle_enter+0x38/0x50
|  do_idle+0x230/0x2c0
|  cpu_startup_entry+0x24/0x30
|  rest_init+0x110/0x190
|  arch_post_acpi_subsys_init+0x0/0x18
|  start_kernel+0x6f8/0x738
|  __primary_switched+0xbc/0xc4

IIUC what's happenign here is the PSCI cpuidle driver has entered idle and RCU
is no longer watching when arm64's cpu_suspend() manipulates DAIF. Our
local_daif_*() helpers poke lockdep and tracing, hence the call to
trace_hardirqs_off() and the RCU usage.

I think we need RCU to be watching all the way down to cpu_suspend(), and it's
cpu_suspend() that should actually enter/exit idle context. That and we need to
make cpu_suspend() and the low-level PSCI invocation noinstr.

I'm not sure whether 32-bit will have a similar issue or not.

I'm surprised no-one else who has tested has seen this; I suspect people
haven't enabled lockdep and friends. :/

Thanks,
Mark. 

Powered by blists - more mailing lists