Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934325Ab1FWSWV (ORCPT ); Thu, 23 Jun 2011 14:22:21 -0400 Received: from mga11.intel.com ([192.55.52.93]:30095 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933225Ab1FWSWM (ORCPT ); Thu, 23 Jun 2011 14:22:12 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.65,414,1304319600"; d="scan'208";a="22073803" Message-Id: <20110623182056.982526827@sbsiddha-MOBL3.sc.intel.com> User-Agent: quilt/0.47-1 Date: Thu, 23 Jun 2011 11:19:28 -0700 From: Suresh Siddha To: mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com, trenn@suse.de, prarit@redhat.com, tj@kernel.org, rusty@rustcorp.com.au, a.p.zijlstra@chello.nl, akpm@linux-foundation.org, torvalds@linux-foundation.org Cc: linux-kernel@vger.kernel.org, suresh.b.siddha@intel.com, youquan.song@intel.com Subject: [patch v2 3/4] stop_machine: implement stop_machine_from_inactive_cpu() References: <20110623181925.983511592@sbsiddha-MOBL3.sc.intel.com> Content-Disposition: inline; filename=implement_stop_machine_from_inactive_cpu.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5521 Lines: 161 From: Tejun Heo Currently, mtrr wants stop_machine functionality while a CPU is being brought up. As stop_machine() requires the calling CPU to be active, mtrr implements its own stop_machine using stop_one_cpu() on each online CPU. This doesn't only unnecessarily duplicate complex logic but also introduces a possibility of deadlock when it races against the generic stop_machine(). This patch implements stop_machine_from_inactive_cpu() to serve such use cases. Its functionality is basically the same as stop_machine(); however, it should be called from a CPU which isn't active and doesn't depend on working scheduling on the calling CPU. This is achieved by using busy loops for synchronization and open-coding stop_cpus queuing and waiting with direct invocation of fn() for local CPU inbetween. Signed-off-by: Tejun Heo Signed-off-by: Suresh Siddha Cc: Ingo Molnar Cc: Andrew Morton Cc: Linus Torvalds Cc: Peter Zijlstra --- include/linux/stop_machine.h | 14 ++++++++- kernel/stop_machine.c | 62 ++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 73 insertions(+), 3 deletions(-) Index: linux-2.6-tip/kernel/stop_machine.c =================================================================== --- linux-2.6-tip.orig/kernel/stop_machine.c +++ linux-2.6-tip/kernel/stop_machine.c @@ -439,8 +439,15 @@ static int stop_machine_cpu_stop(void *d struct stop_machine_data *smdata = data; enum stopmachine_state curstate = STOPMACHINE_NONE; int cpu = smp_processor_id(), err = 0; + unsigned long flags; bool is_active; + /* + * When called from stop_machine_from_inactive_cpu(), irq might + * already be disabled. Save the state and restore it on exit. + */ + local_save_flags(flags); + if (!smdata->active_cpus) is_active = cpu == cpumask_first(cpu_online_mask); else @@ -468,7 +475,7 @@ static int stop_machine_cpu_stop(void *d } } while (curstate != STOPMACHINE_EXIT); - local_irq_enable(); + local_irq_restore(flags); return err; } @@ -495,4 +502,57 @@ int stop_machine(int (*fn)(void *), void } EXPORT_SYMBOL_GPL(stop_machine); +/** + * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU + * @fn: the function to run + * @data: the data ptr for the @fn() + * @cpus: the cpus to run the @fn() on (NULL = any online cpu) + * + * This is identical to stop_machine() but can be called from a CPU which + * is not active. The local CPU is in the process of hotplug (so no other + * CPU hotplug can start) and not marked active and doesn't have enough + * context to sleep. + * + * This function provides stop_machine() functionality for such state by + * using busy-wait for synchronization and executing @fn directly for local + * CPU. + * + * CONTEXT: + * Local CPU is inactive. Temporarily stops all active CPUs. + * + * RETURNS: + * 0 if all executions of @fn returned 0, any non zero return value if any + * returned non zero. + */ +int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data, + const struct cpumask *cpus) +{ + struct stop_machine_data smdata = { .fn = fn, .data = data, + .active_cpus = cpus }; + struct cpu_stop_done done; + int ret; + + /* Local CPU must be inactive and CPU hotplug in progress. */ + BUG_ON(cpu_active(raw_smp_processor_id())); + smdata.num_threads = num_active_cpus() + 1; /* +1 for local */ + + /* No proper task established and can't sleep - busy wait for lock. */ + while (!mutex_trylock(&stop_cpus_mutex)) + cpu_relax(); + + /* Schedule work on other CPUs and execute directly for local CPU */ + set_state(&smdata, STOPMACHINE_PREPARE); + cpu_stop_init_done(&done, num_active_cpus()); + queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata, + &done); + ret = stop_machine_cpu_stop(&smdata); + + /* Busy wait for completion. */ + while (!completion_done(&done.completion)) + cpu_relax(); + + mutex_unlock(&stop_cpus_mutex); + return ret ?: done.ret; +} + #endif /* CONFIG_STOP_MACHINE */ Index: linux-2.6-tip/include/linux/stop_machine.h =================================================================== --- linux-2.6-tip.orig/include/linux/stop_machine.h +++ linux-2.6-tip/include/linux/stop_machine.h @@ -126,15 +126,19 @@ int stop_machine(int (*fn)(void *), void */ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus); +int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data, + const struct cpumask *cpus); + #else /* CONFIG_STOP_MACHINE && CONFIG_SMP */ static inline int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) { + unsigned long flags; int ret; - local_irq_disable(); + local_irq_save(flags); ret = fn(data); - local_irq_enable(); + local_irq_restore(flags); return ret; } @@ -144,5 +148,11 @@ static inline int stop_machine(int (*fn) return __stop_machine(fn, data, cpus); } +static inline int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data, + const struct cpumask *cpus) +{ + return __stop_machine(fn, data, cpus); +} + #endif /* CONFIG_STOP_MACHINE && CONFIG_SMP */ #endif /* _LINUX_STOP_MACHINE */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/