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Subject[PATCH] [5/6] scheduler: Protect important kernel threads against normalize_rt
Date

Not only the migration thread, but also softlockup and stop machine
need to be protected against normalize_rt(). Instead of checking
for them all I added a new process flag for this.

This was the last available bit in 32bit task->flags, sorry for that.

This removes the is_migration_thread macro added in the last patch
again because it is not needed anymore.

Signed-off-by: Andi Kleen <ak@suse.de>

Index: linux-2.6-sched-devel/include/linux/sched.h
===================================================================
--- linux-2.6-sched-devel.orig/include/linux/sched.h
+++ linux-2.6-sched-devel/include/linux/sched.h
@@ -1330,6 +1330,7 @@ static inline void put_task_struct(struc
#define PF_MEMPOLICY 0x10000000 /* Non-default NUMA mempolicy */
#define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */
#define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezeable */
+#define PF_RT_PROTECTED 0x80000000 /* RT task protected from sysrq */

/*
* Only the _current_ task can read/write to tsk->flags, but other
Index: linux-2.6-sched-devel/kernel/sched.c
===================================================================
--- linux-2.6-sched-devel.orig/kernel/sched.c
+++ linux-2.6-sched-devel/kernel/sched.c
@@ -74,12 +74,6 @@ unsigned long long __attribute__((weak))
return (unsigned long long)jiffies * (1000000000 / HZ);
}

-#ifdef CONFIG_SMP
-#define is_migration_thread(p, rq) ((p) == (rq)->migration_thread)
-#else
-#define is_migration_thread(p, rq) 0
-#endif
-
/*
* Convert user-nice values [ -20 ... 0 ... 19 ]
* to static priority [ MAX_RT_PRIO..MAX_PRIO-1 ],
@@ -5305,6 +5299,7 @@ migration_call(struct notifier_block *nf
kthread_bind(p, cpu);
/* Must be high prio: stop_machine expects to yield to it. */
rq = task_rq_lock(p, &flags);
+ p->flags |= PF_RT_PROTECTED;
__setscheduler(rq, p, SCHED_FIFO, MAX_RT_PRIO-1);
task_rq_unlock(rq, &flags);
cpu_rq(cpu)->migration_thread = p;
@@ -6583,7 +6578,7 @@ void normalize_rt_tasks(void)
spin_lock_irqsave(&p->pi_lock, flags);
rq = __task_rq_lock(p);

- if (!is_migration_thread(p, rq))
+ if (!(p->flags & PF_RT_PROTECTED))
normalize_task(rq, p);

__task_rq_unlock(rq);
Index: linux-2.6-sched-devel/kernel/softlockup.c
===================================================================
--- linux-2.6-sched-devel.orig/kernel/softlockup.c
+++ linux-2.6-sched-devel/kernel/softlockup.c
@@ -116,6 +116,7 @@ static int watchdog(void * __bind_cpu)
{
struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };

+ current->flags |= PF_RT_PROTECTED;
sched_setscheduler(current, SCHED_FIFO, &param);

/* initialize timestamp */
Index: linux-2.6-sched-devel/kernel/stop_machine.c
===================================================================
--- linux-2.6-sched-devel.orig/kernel/stop_machine.c
+++ linux-2.6-sched-devel/kernel/stop_machine.c
@@ -187,6 +187,7 @@ struct task_struct *__stop_machine_run(i
if (!IS_ERR(p)) {
struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };

+ p->flags |= PF_RT_PROTECTED;
/* One high-prio thread per cpu. We'll do this one. */
sched_setscheduler(p, SCHED_FIFO, &param);
kthread_bind(p, cpu);
-
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