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Subject[PATCH] cpu_stop: add dummy implementation for UP
When !CONFIG_SMP, cpu_stop functions weren't defined at all which
could lead to build failures if UP code uses cpu_stop facility. Add
dummy cpu_stop implementation for UP. The waiting variants execute
the work function directly with preempt disabled and
stop_one_cpu_nowait() schedules a workqueue work.

Makefile and ifdefs around stop_machine implementation are updated to
accomodate CONFIG_SMP && !CONFIG_STOP_MACHINE case.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Ingo Molnar <mingo@elte.hu>
---
This patch should fix possible build issues on UP configurations.
I've published the patch to the cpu_stop branch.

git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git cpu_stop

Ingo, can you please pull from it?

Thank you.

include/linux/stop_machine.h | 69 ++++++++++++++++++++++++++++++++++++++----
kernel/Makefile | 2 +-
kernel/stop_machine.c | 4 ++
3 files changed, 68 insertions(+), 7 deletions(-)

diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
index 0e552e7..6b524a0 100644
--- a/include/linux/stop_machine.h
+++ b/include/linux/stop_machine.h
@@ -6,8 +6,6 @@
#include <linux/list.h>
#include <asm/system.h>

-#if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
-
/*
* stop_cpu[s]() is simplistic per-cpu maximum priority cpu
* monopolization mechanism. The caller can specify a non-sleeping
@@ -18,9 +16,10 @@
* up and requests are guaranteed to be served as long as the target
* cpus are online.
*/
-
typedef int (*cpu_stop_fn_t)(void *arg);

+#ifdef CONFIG_SMP
+
struct cpu_stop_work {
struct list_head list; /* cpu_stopper->works */
cpu_stop_fn_t fn;
@@ -34,12 +33,70 @@ void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg);
int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg);

+#else /* CONFIG_SMP */
+
+#include <linux/workqueue.h>
+
+struct cpu_stop_work {
+ struct work_struct work;
+ cpu_stop_fn_t fn;
+ void *arg;
+};
+
+static inline int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
+{
+ int ret = -ENOENT;
+ preempt_disable();
+ if (cpu == smp_processor_id())
+ ret = fn(arg);
+ preempt_enable();
+ return ret;
+}
+
+static void stop_one_cpu_nowait_workfn(struct work_struct *work)
+{
+ struct cpu_stop_work *stwork =
+ container_of(work, struct cpu_stop_work, work);
+ preempt_disable();
+ stwork->fn(stwork->arg);
+ preempt_enable();
+}
+
+static inline void stop_one_cpu_nowait(unsigned int cpu,
+ cpu_stop_fn_t fn, void *arg,
+ struct cpu_stop_work *work_buf)
+{
+ if (cpu == smp_processor_id()) {
+ INIT_WORK(&work_buf->work, stop_one_cpu_nowait_workfn);
+ work_buf->fn = fn;
+ work_buf->arg = arg;
+ schedule_work(&work_buf->work);
+ }
+}
+
+static inline int stop_cpus(const struct cpumask *cpumask,
+ cpu_stop_fn_t fn, void *arg)
+{
+ if (cpumask_test_cpu(raw_smp_processor_id(), cpumask))
+ return stop_one_cpu(raw_smp_processor_id(), fn, arg);
+ return -ENOENT;
+}
+
+static inline int try_stop_cpus(const struct cpumask *cpumask,
+ cpu_stop_fn_t fn, void *arg)
+{
+ return stop_cpus(cpumask, fn, arg);
+}
+
+#endif /* CONFIG_SMP */
+
/*
* stop_machine "Bogolock": stop the entire machine, disable
* interrupts. This is a very heavy lock, which is equivalent to
* grabbing every spinlock (and more). So the "read" side to such a
* lock is anything which disables preeempt.
*/
+#if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)

/**
* stop_machine: freeze the machine on all CPUs and run this function
@@ -67,7 +124,7 @@ int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus);
*/
int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus);

-#else
+#else /* CONFIG_STOP_MACHINE && CONFIG_SMP */

static inline int stop_machine(int (*fn)(void *), void *data,
const struct cpumask *cpus)
@@ -79,5 +136,5 @@ static inline int stop_machine(int (*fn)(void *), void *data,
return ret;
}

-#endif /* CONFIG_SMP */
-#endif /* _LINUX_STOP_MACHINE */
+#endif /* CONFIG_STOP_MACHINE && CONFIG_SMP */
+#endif /* _LINUX_STOP_MACHINE */
diff --git a/kernel/Makefile b/kernel/Makefile
index a987aa1..149e18e 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -68,7 +68,7 @@ obj-$(CONFIG_USER_NS) += user_namespace.o
obj-$(CONFIG_PID_NS) += pid_namespace.o
obj-$(CONFIG_IKCONFIG) += configs.o
obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o
-obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
+obj-$(CONFIG_SMP) += stop_machine.o
obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
obj-$(CONFIG_AUDIT) += audit.o auditfilter.o audit_watch.o
obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 5b20141..ef51d1f 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -375,6 +375,8 @@ static int __init cpu_stop_init(void)
}
early_initcall(cpu_stop_init);

+#ifdef CONFIG_STOP_MACHINE
+
/* This controls the threads on each CPU. */
enum stopmachine_state {
/* Dummy starting state for thread. */
@@ -477,3 +479,5 @@ int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
return ret;
}
EXPORT_SYMBOL_GPL(stop_machine);
+
+#endif /* CONFIG_STOP_MACHINE */
--
1.6.4.2


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