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Date: Tue, 14 Jun 2011 19:06:58 +0200
From: Tejun Heo <tj@...nel.org>
To: x86@...nel.org, mingo@...e.hu, akpm@...ux-foundation.org,
torvalds@...ux-foundation.org, suresh.b.siddha@...el.com,
a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org
Cc: Tejun Heo <tj@...nel.org>
Subject: [PATCH 3/3] stop_machine: implement stop_machine_from_offline_cpu()
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@...nel.org>
Cc: Suresh Siddha <suresh.b.siddha@...el.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.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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