sched: move_task_off_dead_cpu(): Remove retry logic

commit c1804d547dc098363443667609c272d1e4d15ee8 upstream

The previous patch preserved the retry logic, but it looks unneeded.

__migrate_task() can only fail if we raced with migration after we dropped
the lock, but in this case the caller of set_cpus_allowed/etc must initiate
migration itself if ->on_rq == T.

We already fixed p->cpus_allowed, the changes in active/online masks must
be visible to racer, it should migrate the task to online cpu correctly.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100315091014.GA9138@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/kernel/sched.c b/kernel/sched.c
index d92a62215b8cc8cbcfe8d8c6ff4ce7031d9d8fca..c40bf288fae0972c380e2dea25253cb87b711aa4 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7407,7 +7407,7 @@ static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p)
        struct rq *rq = cpu_rq(dead_cpu);
        int needs_cpu, uninitialized_var(dest_cpu);
        unsigned long flags;
-again:
+
        local_irq_save(flags);
 
        spin_lock(&rq->lock);
@@ -7415,14 +7415,13 @@ again:
        if (needs_cpu)
                dest_cpu = select_fallback_rq(dead_cpu, p);
        spin_unlock(&rq->lock);
-
-       /* It can have affinity changed while we were choosing. */
+       /*
+        * It can only fail if we race with set_cpus_allowed(),
+        * in the racer should migrate the task anyway.
+        */
        if (needs_cpu)
-               needs_cpu = !__migrate_task(p, dead_cpu, dest_cpu);
+               __migrate_task(p, dead_cpu, dest_cpu);
        local_irq_restore(flags);
-
-       if (unlikely(needs_cpu))
-               goto again;
 }
 
 /*