Re: [PATCH 15/36] cpuidle,cpu_pm: Remove RCU fiddling from cpu_pm_{enter,exit}()
From: Mark Rutland <mark.rutland@arm.com>
Date: 2022-06-14 16:15:36
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linux-acpi, linux-alpha, linux-arch, linux-arm-msm, linux-clk, linux-m68k, linux-mips, linux-omap, linux-perf-users, linux-pm, linux-riscv, linux-s390, linux-sh, linux-tegra, linux-um, lkml, rcu, sparclinux, virtualization, xen-devel
arndb.de>, ulli.kroll@googlemail.com, vgupta@kernel.org, linux-clk@vger.kernel.org, josh@joshtriplett.org, rostedt@goodmis.org, rcu@vger.kernel.org, bp@alien8.de, bcain@quicinc.com, tsbogend@alpha.franken.de, linux-parisc@vger.kernel.org, sudeep.holla@arm.com, shawnguo@kernel.org, davem@davemloft.net, dalias@libc.org, tony@atomide.com, amakhalov@vmware.com, bjorn.andersson@linaro.org, hpa@zytor.com, sparclinux@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-riscv@lists.infradead.org, anton.ivanov@cambridgegreys.com, jonas@southpole.se, yury.norov@gmail.com, richard@nod.at, x86@kernel.org, linux@armlinux.org.uk, mingo@redhat.com, aou@eecs.berkeley.edu, paulmck@kernel.org, hca@linux.ibm.com, stefan.kristiansson@saunalahti.fi, openrisc@lists.librecores.org, paul.walmsley@sifive.com, linux-tegra@vger.kernel.org, namhyung@kernel.org, andriy.shevchenko@linux.intel.com, jpoimboe@kernel.org, jgross@suse.com, monstr@monstr.eu, linux-mips@vger.kernel.org, palmer@dabbelt.com, anup@brainfa ult.org, ink@jurassic.park.msu.ru, johannes@sipsolutions.net, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" [off-list ref] On Wed, Jun 08, 2022 at 04:27:38PM +0200, Peter Zijlstra wrote:
All callers should still have RCU enabled.
IIUC with that true we should be able to drop the RCU_NONIDLE() from drivers/perf/arm_pmu.c, as we only needed that for an invocation via a pm notifier. I should be able to give that a spin on some hardware.
quoted hunk ↗ jump to hunk
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/cpu_pm.c | 9 --------- 1 file changed, 9 deletions(-)--- a/kernel/cpu_pm.c +++ b/kernel/cpu_pm.c@@ -30,16 +30,9 @@ static int cpu_pm_notify(enum cpu_pm_eve { int ret; - /* - * This introduces a RCU read critical section, which could be - * disfunctional in cpu idle. Copy RCU_NONIDLE code to let RCU know - * this. - */ - rcu_irq_enter_irqson(); rcu_read_lock(); ret = raw_notifier_call_chain(&cpu_pm_notifier.chain, event, NULL); rcu_read_unlock(); - rcu_irq_exit_irqson();
To make this easier to debug, is it worth adding an assertion that RCU is watching here? e.g. RCU_LOCKDEP_WARN(!rcu_is_watching(), "cpu_pm_notify() used illegally from EQS");
quoted hunk ↗ jump to hunk
return notifier_to_errno(ret); }@@ -49,11 +42,9 @@ static int cpu_pm_notify_robust(enum cpu unsigned long flags; int ret; - rcu_irq_enter_irqson(); raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags); ret = raw_notifier_call_chain_robust(&cpu_pm_notifier.chain, event_up, event_down, NULL); raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags); - rcu_irq_exit_irqson();
... and likewise here? Thanks, Mark.
return notifier_to_errno(ret); }