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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 <tj@kernel.org>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: H. Peter Anvin <hpa@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Tejun Heo <htejun@gmail.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jeremy Fitzhardinge 2011-10-31 17:11:15 -07:00 committed by Linus Torvalds
parent aaaa287b89
commit f445027e4e
1 changed files with 22 additions and 0 deletions
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22
kernel/stop_machine.c
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@ -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 +488,25 @@ 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 stop_machine() has been
* initialized.
*/
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);