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McKenney" To: Peter Zijlstra Subject: Re: [PATCH 16/36] rcu: Fix rcu_idle_exit() Message-ID: <20220615004412.GA5766@paulmck-ThinkPad-P17-Gen-1> References: <20220608142723.103523089@infradead.org> <20220608144516.935970247@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220608144516.935970247@infradead.org> X-Mailman-Approved-At: Thu, 16 Jun 2022 11:54:30 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: paulmck@kernel.org Cc: juri.lelli@redhat.com, rafael@kernel.org, linus.walleij@linaro.org, bsegall@google.com, guoren@kernel.org, pavel@ucw.cz, agordeev@linux.ibm.com, srivatsa@csail.mit.edu, linux-arch@vger.kernel.org, vincent.guittot@linaro.org, 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, borntraeger@linux.ibm.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, paulus@samba.org, mark.rutland@arm.com, linux-ia64@vger.kernel.org, dave.hansen@linux.intel.com, virtualizatio n@lists.linux-foundation.org, James.Bottomley@HansenPartnership.com, jcmvbkbc@gmail.com, thierry.reding@gmail.com, kernel@xen0n.name, quic_neeraju@quicinc.com, linux-s390@vger.kernel.org, vschneid@redhat.com, john.ogness@linutronix.de, ysato@users.sourceforge.jp, linux-sh@vger.kernel.org, festevam@gmail.com, deller@gmx.de, daniel.lezcano@linaro.org, jonathanh@nvidia.com, mathieu.desnoyers@efficios.com, frederic@kernel.org, lenb@kernel.org, linux-xtensa@linux-xtensa.org, kernel@pengutronix.de, gor@linux.ibm.com, linux-arm-msm@vger.kernel.org, linux-alpha@vger.kernel.org, linux-m68k@lists.linux-m68k.org, shorne@gmail.com, linux-arm-kernel@lists.infradead.org, chris@zankel.net, sboyd@kernel.org, dinguyen@kernel.org, bristot@redhat.com, alexander.shishkin@linux.intel.com, lpieralisi@kernel.org, linux@rasmusvillemoes.dk, joel@joelfernandes.org, will@kernel.org, boris.ostrovsky@oracle.com, khilman@kernel.org, linux-csky@vger.kernel.org, pv-drivers@vmware.com, linux-snps-arc@lists.infradea d.org, mgorman@suse.de, jacob.jun.pan@linux.intel.com , Arnd Bergmann , 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, 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@brain fault.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" On Wed, Jun 08, 2022 at 04:27:39PM +0200, Peter Zijlstra wrote: > Current rcu_idle_exit() is terminally broken because it uses > local_irq_{save,restore}(), which are traced which uses RCU. > > However, now that all the callers are sure to have IRQs disabled, we > can remove these calls. > > Signed-off-by: Peter Zijlstra (Intel) > Acked-by: Paul E. McKenney We have some fun conflicts between this series and Frederic's context-tracking series. But it looks like these can be resolved by: 1. A patch on top of Frederic's series that provides the old rcu_*() names for the functions now prefixed with ct_*() such as ct_idle_exit(). 2. Another patch on top of Frederic's series that takes the changes remaining from this patch, shown below. Frederic's series uses raw_local_irq_save() and raw_local_irq_restore(), which can then be removed. Or is there a better way to do this? Thanx, Paul ------------------------------------------------------------------------ commit f64cee8c159e9863a74594efe3d33fb513a6a7b5 Author: Peter Zijlstra Date: Tue Jun 14 17:24:43 2022 -0700 context_tracking: Interrupts always disabled for ct_idle_exit() Now that the idle-loop cleanups have ensured that rcu_idle_exit() is always invoked with interrupts disabled, remove the interrupt disabling in favor of a debug check. Signed-off-by: Peter Zijlstra Cc: Frederic Weisbecker Signed-off-by: Paul E. McKenney diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c index 1da44803fd319..99310cf5b0254 100644 --- a/kernel/context_tracking.c +++ b/kernel/context_tracking.c @@ -332,11 +332,8 @@ EXPORT_SYMBOL_GPL(ct_idle_enter); */ void noinstr ct_idle_exit(void) { - unsigned long flags; - - raw_local_irq_save(flags); + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled()); ct_kernel_enter(false, RCU_DYNTICKS_IDX - CONTEXT_IDLE); - raw_local_irq_restore(flags); } EXPORT_SYMBOL_GPL(ct_idle_exit);