Messages in this thread Patch in this message | | | From | Tejun Heo <> | Subject | [PATCH 3/3] stop_machine: implement stop_machine_from_offline_cpu() | Date | Tue, 14 Jun 2011 19:06:58 +0200 |
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Currently, mtrr wants stop_machine functionality while a CPU is being brought up. As stop_machine() requires the calling CPU to be online, 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_offline_cpu() to serve such use cases. Its functionality is basically the same to stop_machine(); however, it should be called from a CPU which isn't online 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 queueing and waiting with direct invocation of fn() for local CPU inbetween.
This is inspired from Suresh's patch to implement similar functionality into stop_machine().
http://article.gmane.org/gmane.linux.kernel/1154384
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Suresh Siddha <suresh.b.siddha@intel.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> --- include/linux/stop_machine.h | 14 ++++++++- kernel/stop_machine.c | 61 +++++++++++++++++++++++++++++++++++++++++- 2 files changed, 72 insertions(+), 3 deletions(-)
diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h index 4f1a73c..c78ef6a 100644 --- a/include/linux/stop_machine.h +++ b/include/linux/stop_machine.h @@ -99,18 +99,28 @@ static inline int try_stop_cpus(const struct cpumask *cpumask, #if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP) int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus); +int stop_machine_from_offline_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; } +static inline int stop_machine_from_offline_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 */ diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 198973f..ff648d9 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -439,8 +439,15 @@ static int stop_machine_cpu_stop(void *data) 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_offline_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 *data) } } while (curstate != STOPMACHINE_EXIT); - local_irq_enable(); + local_irq_restore(flags); return err; } @@ -511,4 +518,56 @@ int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) } EXPORT_SYMBOL_GPL(stop_machine); +/** + * stop_machine_from_offline_cpu - stop_machine() from offline 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 + * isn't online. The local CPU is in the process of hotplug (so no other + * CPU hotplug can start) and not marked online 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 offline. Temporarily stops all online CPUs. + * + * RETURNS: + * 0 if all executions of @fn returned 0, any non zero return value if any + * returned non zero. + */ +int stop_machine_from_offline_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 offline and CPU hotplug in progress. */ + BUG_ON(cpu_online(raw_smp_processor_id())); + smdata.num_threads = num_online_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_online_cpus()); + stop_cpus_queue(cpu_online_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 */ -- 1.7.5.2
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