sched: do not normalize kernel threads via SysRq-N

do not normalize kernel threads via SysRq-N: the migration threads,
softlockup threads, etc. might be essential for the system to
function properly. So only zap user tasks.

pointed out by Andi Kleen.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 11 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index fc61b1fc67d5..791dd08c692f 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -365,15 +365,6 @@ static inline int cpu_of(struct rq *rq)
 #endif
 }
 
-static inline int is_migration_thread(struct task_struct *p, struct rq *rq)
-{
-#ifdef CONFIG_SMP
-        return p == rq->migration_thread;
-#else
-        return 0;
-#endif
-}
-
 /*
  * Update the per-runqueue clock, as finegrained as the platform can give
  * us, but without assuming monotonicity, etc.:
@@ -6563,6 +6554,12 @@ void normalize_rt_tasks(void)
 
         read_lock_irq(&tasklist_lock);
         do_each_thread(g, p) {
+                /*
+                 * Only normalize user tasks:
+                 */
+                if (!p->mm)
+                        continue;
+
                 p->se.exec_start                = 0;
 #ifdef CONFIG_SCHEDSTATS
                 p->se.wait_start                = 0;
@@ -6584,8 +6581,7 @@ void normalize_rt_tasks(void)
                 spin_lock_irqsave(&p->pi_lock, flags);
                 rq = __task_rq_lock(p);
 
-                if (!is_migration_thread(p, rq))
-                        normalize_task(rq, p);
+                normalize_task(rq, p);
 
                 __task_rq_unlock(rq);
                 spin_unlock_irqrestore(&p->pi_lock, flags);