* [PATCH] sched: Assign !p->on_cpu to the second parameter of smp_cond_load_acquire()
@ 2016-07-01 3:08 T.Zhou
2016-07-01 6:55 ` Peter Zijlstra
0 siblings, 1 reply; 2+ messages in thread
From: T.Zhou @ 2016-07-01 3:08 UTC (permalink / raw)
To: peterz; +Cc: mingo, linux-kernel
The second parameter of smp_cond_load_acquire() should be !p->on_cpu
cause remote wakeup need to ensure that: if the task is running on
prev cpu, it should be descheduled before doing the actual wakeup.
Signed-off-by: T.Zhou <t1zhou@163.com>
---
kernel/sched/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3387e4f..8e6fef6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2047,7 +2047,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
* This ensures that tasks getting woken will be fully ordered against
* their previous state and preserve Program Order.
*/
- smp_cond_load_acquire(&p->on_cpu, !VAL);
+ smp_cond_load_acquire(&p->on_cpu, !p->on_cpu);
p->sched_contributes_to_load = !!task_contributes_to_load(p);
p->state = TASK_WAKING;
--
2.7.3
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] sched: Assign !p->on_cpu to the second parameter of smp_cond_load_acquire()
2016-07-01 3:08 [PATCH] sched: Assign !p->on_cpu to the second parameter of smp_cond_load_acquire() T.Zhou
@ 2016-07-01 6:55 ` Peter Zijlstra
0 siblings, 0 replies; 2+ messages in thread
From: Peter Zijlstra @ 2016-07-01 6:55 UTC (permalink / raw)
To: T.Zhou; +Cc: mingo, linux-kernel
On Fri, Jul 01, 2016 at 11:08:01AM +0800, T.Zhou wrote:
> - smp_cond_load_acquire(&p->on_cpu, !VAL);
> + smp_cond_load_acquire(&p->on_cpu, !p->on_cpu);
Huh, what?! No, the second parameter should very much include VAL, which
gets assigned the value of *(&p->on_cpu).
Go read the macro, it even has a comment on.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2016-07-01 3:08 [PATCH] sched: Assign !p->on_cpu to the second parameter of smp_cond_load_acquire() T.Zhou
2016-07-01 6:55 ` Peter Zijlstra
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