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. ]

Jeremy Fitzhardinge committed 15 years ago

Commit f4450271 parent aaaa2871 file · +22 −0Browse files

Showing the changes to kernel (1 of 1 file). Show all

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kernel/stop_machine.c+22−0

@@ -41,6 +41,7 @@ struct cpu_stopper { · 40 unmodified lines
41	41	};
42	42
43	43	static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
	44	+static bool stop_machine_initialized = false;
44	45
45	46	static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
46	47	{
@@ -386,6 +387,8 @@ static int __init cpu_stop_init(void) · 339 unmodified lines
386	387	cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
387	388	register_cpu_notifier(&cpu_stop_cpu_notifier);
388	389
	390	+ stop_machine_initialized = true;
	391	+
389	392	return 0;
390	393	}
391	394	early_initcall(cpu_stop_init);
@@ -485,6 +488,25 @@ int __stop_machine(int (fn)(void ), void data, const struct cpumask cpus) · 93 unmodified lines
485	488	.num_threads = num_online_cpus(),
486	489	.active_cpus = cpus };
487	490
	491	+ if (!stop_machine_initialized) {
	492	+ /*
	493	+ * Handle the case where stop_machine() is called
	494	+ * early in boot before stop_machine() has been
	495	+ * initialized.
	496	+ */
	497	+ unsigned long flags;
	498	+ int ret;
	499	+
	500	+ WARN_ON_ONCE(smdata.num_threads != 1);
	501	+
	502	+ local_irq_save(flags);
	503	+ hard_irq_disable();
	504	+ ret = (*fn)(data);
	505	+ local_irq_restore(flags);
	506	+
	507	+ return ret;
	508	+ }
	509	+
488	510	/* Set the initial state and stop all online cpus. */
489	511	set_state(&smdata, STOPMACHINE_PREPARE);
490	512	return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);