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sched: move_task_off_dead_cpu(): Remove retry logic
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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>
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Oleg Nesterov authored and Ingo Molnar committed Apr 2, 2010
1 parent 1445c08 commit c1804d5
Showing 1 changed file with 6 additions and 7 deletions.
13 changes: 6 additions & 7 deletions kernel/sched.c
Original file line number Diff line number Diff line change
Expand Up @@ -5456,22 +5456,21 @@ 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);

raw_spin_lock(&rq->lock);
needs_cpu = (task_cpu(p) == dead_cpu) && (p->state != TASK_WAKING);
if (needs_cpu)
dest_cpu = select_fallback_rq(dead_cpu, p);
raw_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;
}

/*
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