From 779b459eda0ddf8d2138410fc065eb3640bf1569 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Wed, 5 Oct 2011 11:43:24 +1100 Subject: [PATCH] stop_machine: make stop_machine safe and efficient to call early Make stop_machine() safe to call early in boot, before SMP has been set up, by simply calling the callback function directly if there's only one CPU online. [ Fixes from AKPM: - add comment - local_irq_flags, not save_flags - also call hard_irq_disable() for systems which need it Tejun suggested using an explicit flag rather than just looking at the online cpu count. ] Cc: Tejun Heo Cc: Rusty Russell Cc: Peter Zijlstra Cc: H. Peter Anvin Cc: Ingo Molnar Cc: Steven Rostedt Acked-by: Tejun Heo Cc: Tejun Heo Cc: Konrad Rzeszutek Wilk Signed-off-by: Jeremy Fitzhardinge Signed-off-by: Andrew Morton --- kernel/stop_machine.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index e78db365fa83..0ee58f4545ab 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -41,6 +41,7 @@ struct cpu_stopper { }; static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper); +static bool stop_machine_initialized = false; static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo) { @@ -386,6 +387,8 @@ static int __init cpu_stop_init(void) cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu); register_cpu_notifier(&cpu_stop_cpu_notifier); + stop_machine_initialized = true; + return 0; } early_initcall(cpu_stop_init); @@ -485,6 +488,24 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) .num_threads = num_online_cpus(), .active_cpus = cpus }; + if (!stop_machine_initialized) { + /* + * Handle the case where stop_machine() is called early in boot + * before SMP startup. + */ + unsigned long flags; + int ret; + + WARN_ON_ONCE(smdata.num_threads != 1); + + local_irq_save(flags); + hard_irq_disable(); + ret = (*fn)(data); + local_irq_restore(flags); + + return ret; + } + /* Set the initial state and stop all online cpus. */ set_state(&smdata, STOPMACHINE_PREPARE); return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata); -- 2.39.5