Prev: [PATCH] serial: fix possible imx deadlock
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From: Oleg Nesterov on 15 Mar 2010 05:20
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(a)redhat.com>
---

kernel/sched.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

--- 34-rc1/kernel/sched.c~2_XXX_MTODC_DONT_RETRY 2010-03-15 09:40:31.000000000 +0100
+++ 34-rc1/kernel/sched.c 2010-03-15 09:40:44.000000000 +0100
@@ -5517,7 +5517,7 @@ static void move_task_off_dead_cpu(int d
struct rq *rq = cpu_rq(dead_cpu);
int needs_cpu, dest_cpu;
unsigned long flags;
-again:
+
local_irq_save(flags);

raw_spin_lock(&rq->lock);
@@ -5525,14 +5525,13 @@ again:
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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Prev: [PATCH] serial: fix possible imx deadlock
Next: [PATCH 0/6] sched/cpusets fixes, more changes are needed