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Subject[PATCH RT v2] cpu unplug with PREEMPT_LL

v2: less UGLY (less intrusive in sched.c)

With CONFIG_PREEMPT_LL, cpu unplug generates a bunch of
BUG: sleeping function called from invalid context
BUG: scheduling while atomic

To reproduce the problem:
echo 0 > /sys/devices/system/cpu/cpu1/online

This patch should maybe not be included in the RT patch set but it
may be useful to anyone determined to use cpu hotplug with PREEMPT_LL.

This patch was tested on 3.0.36-rt58 since that release has the latest
hotplug patches. I will rework and test this on 3.5-rtX when that is available.

Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
---
include/linux/preempt.h | 10 8 + 2 - 0 !
include/linux/sched.h | 6 3 + 3 - 0 !
kernel/cpu.c | 12 12 + 0 - 0 !
kernel/sched.c | 10 5 + 5 - 0 !
4 files changed, 28 insertions(+), 10 deletions(-)

Index: b/include/linux/preempt.h
===================================================================
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -109,8 +109,10 @@ do { \
# define preempt_disable_nort() do { } while (0)
# define preempt_enable_nort() do { } while (0)
# ifdef CONFIG_SMP
- extern void migrate_disable(void);
- extern void migrate_enable(void);
+ extern void __migrate_disable(void);
+ extern void __migrate_enable(void);
+# define migrate_disable() __migrate_disable()
+# define migrate_enable() __migrate_enable()
# else /* CONFIG_SMP */
# define migrate_disable() do { } while (0)
# define migrate_enable() do { } while (0)
@@ -122,6 +124,10 @@ do { \
# define preempt_enable_nort() preempt_enable()
# define migrate_disable() preempt_disable()
# define migrate_enable() preempt_enable()
+#ifdef CONFIG_PREEMPT_LL
+ extern void __migrate_disable(void);
+ extern void __migrate_enable(void);
+#endif
#endif

#ifdef CONFIG_PREEMPT_NOTIFIERS
Index: b/kernel/cpu.c
===================================================================
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -500,11 +500,19 @@ static int __ref _cpu_down(unsigned int
cpumask_andnot(cpumask, cpu_online_mask, cpumask_of(cpu));
set_cpus_allowed_ptr(current, cpumask);
free_cpumask_var(cpumask);
+#ifdef CONFIG_PREEMPT_LL
+ __migrate_disable();
+#else
migrate_disable();
+#endif
mycpu = smp_processor_id();
if (mycpu == cpu) {
printk(KERN_ERR "Yuck! Still on unplug CPU\n!");
+#ifdef CONFIG_PREEMPT_LL
+ __migrate_enable();
+#else
migrate_enable();
+#endif
return -EBUSY;
}

@@ -557,7 +565,11 @@ static int __ref _cpu_down(unsigned int
out_release:
cpu_unplug_done(cpu);
out_cancel:
+#ifdef CONFIG_PREEMPT_LL
+ __migrate_enable();
+#else
migrate_enable();
+#endif
cpu_hotplug_done();
if (!err)
cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
Index: b/kernel/sched.c
===================================================================
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4192,7 +4192,7 @@ static inline void schedule_debug(struct
schedstat_inc(this_rq(), sched_count);
}

-#if defined(CONFIG_PREEMPT_RT_FULL) && defined(CONFIG_SMP)
+#if (defined(CONFIG_PREEMPT_RT_FULL) || defined(CONFIG_PREEMPT_LL)) && defined(CONFIG_SMP)
#define MIGRATE_DISABLE_SET_AFFIN (1<<30) /* Can't make a negative */
#define migrate_disabled_updated(p) ((p)->migrate_disable & MIGRATE_DISABLE_SET_AFFIN)
#define migrate_disable_count(p) ((p)->migrate_disable & ~MIGRATE_DISABLE_SET_AFFIN)
@@ -4228,7 +4228,7 @@ static inline void update_migrate_disabl
p->migrate_disable |= MIGRATE_DISABLE_SET_AFFIN;
}

-void migrate_disable(void)
+void __migrate_disable(void)
{
struct task_struct *p = current;

@@ -4254,9 +4254,9 @@ void migrate_disable(void)
p->migrate_disable = 1;
preempt_enable();
}
-EXPORT_SYMBOL(migrate_disable);
+EXPORT_SYMBOL(__migrate_disable);

-void migrate_enable(void)
+void __migrate_enable(void)
{
struct task_struct *p = current;
const struct cpumask *mask;
@@ -4306,7 +4306,7 @@ void migrate_enable(void)
unpin_current_cpu();
preempt_enable();
}
-EXPORT_SYMBOL(migrate_enable);
+EXPORT_SYMBOL(__migrate_enable);
#else
static inline void update_migrate_disable(struct task_struct *p) { }
#define migrate_disabled_updated(p) 0
Index: b/include/linux/sched.h
===================================================================
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1260,7 +1260,7 @@ struct task_struct {
#endif

unsigned int policy;
-#ifdef CONFIG_PREEMPT_RT_FULL
+#if defined(CONFIG_PREEMPT_RT_FULL) || defined(CONFIG_PREEMPT_LL)
int migrate_disable;
#ifdef CONFIG_SCHED_DEBUG
int migrate_disable_atomic;
@@ -2678,7 +2678,7 @@ static inline void set_task_cpu(struct t

static inline int __migrate_disabled(struct task_struct *p)
{
-#ifdef CONFIG_PREEMPT_RT_FULL
+#if defined(CONFIG_PREEMPT_RT_FULL) || defined(CONFIG_PREEMPT_LL)
return p->migrate_disable;
#else
return 0;
@@ -2688,7 +2688,7 @@ static inline int __migrate_disabled(str
/* Future-safe accessor for struct task_struct's cpus_allowed. */
static inline const struct cpumask *tsk_cpus_allowed(struct task_struct *p)
{
-#ifdef CONFIG_PREEMPT_RT_FULL
+#if defined(CONFIG_PREEMPT_RT_FULL) || defined(CONFIG_PREEMPT_LL)
if (p->migrate_disable)
return cpumask_of(task_cpu(p));
#endif


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