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Subject[PATCH RFC V4 02/10] stop_machine: make stop_machine safe and efficient to call early
Date
From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

Make stop_machine() safe to call early in boot, before stop_machine()
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. ]

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: H. Peter Anvin <hpa@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
kernel/stop_machine.c | 22 ++++++++++++++++++++++
1 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index ba5070c..d3f960a 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 +488,25 @@ 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);
--
1.7.6.4


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