From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Rutland Subject: Re: [PATCH 15/36] cpuidle,cpu_pm: Remove RCU fiddling from cpu_pm_{enter,exit}() Date: Tue, 14 Jun 2022 17:53:25 +0100 Message-ID: References: <20220608142723.103523089@infradead.org> <20220608144516.871305980@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" To: Peter Zijlstra Cc: juri.lelli@redhat.com, rafael@kernel.org, benh@kernel.crashing.org, linus.walleij@linaro.org, bsegall@google.com, guoren@kernel.org, pavel@ucw.cz, agordeev@linux.ibm.com, linux-arch@vger.kernel.org, vincent.guittot@linaro.org, mpe@ellerman.id.au, chenhuacai@kernel.org, linux-acpi@vger.kernel.org, agross@kernel.org, geert@linux-m68k.org, linux-imx@nxp.com, catalin.marinas@arm.com, xen-devel@lists.xenproject.org, mattst88@gmail.com, mturquette@baylibre.com, sammy@sammy.net, pmladek@suse.com, linux-pm@vger.kernel.org, jiangshanlai@gmail.com, Sascha Hauer , linux-um@lists.infradead.org, acme@kernel.org, tglx@linutronix.de, linux-omap@vger.kernel.org, dietmar.eggemann@arm.com, rth@twiddle.net, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, senozhatsky@chromium.org, svens@linux.ibm.com, jolsa@kernel.org, paul On Tue, Jun 14, 2022 at 06:42:14PM +0200, Peter Zijlstra wrote: > On Tue, Jun 14, 2022 at 05:13:16PM +0100, Mark Rutland wrote: > > 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. > > > > > > > > Signed-off-by: Peter Zijlstra (Intel) > > > --- > > > 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"); > > > > My understanding is that rcu_read_lock() implies something along those > lines when PROVE_RCU. Ah, duh. Given that: Acked-by: Mark Rutland Mark.