Hi,
Just for info , the patch that I have shared earlier with pi_lock
approach has been tested since last one month and no issue has been
observed,
https://lkml.org/lkml/2018/4/25/189
Can we take this if it looks good?
Regards
Gaurav
On 6/5/2018 10:05 PM, Oleg Nesterov wrote:
On 06/05, Peter Zijlstra wrote:
On Tue, Jun 05, 2018 at 05:22:12PM +0200, Peter Zijlstra wrote:
OK, but __kthread_parkme() can be preempted before it calls schedule(), so the
caller still can be migrated? Plus kthread_park_complete() can be called twice.
Argh... I forgot TASK_DEAD does the whole thing with preempt_disable().
Let me stare at that a bit.
This should ensure we only ever complete when we read PARKED, right?
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8d59b259af4a..e513b4600796 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2641,7 +2641,7 @@ prepare_task_switch(struct rq *rq, struct task_struct *prev,
* past. prev == current is still correct but we need to recalculate this_rq
* because prev may have moved to another CPU.
*/
-static struct rq *finish_task_switch(struct task_struct *prev)
+static struct rq *finish_task_switch(struct task_struct *prev, bool preempt)
__releases(rq->lock)
{
struct rq *rq = this_rq();
@@ -2674,7 +2674,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
*
* We must observe prev->state before clearing prev->on_cpu (in
* finish_task), otherwise a concurrent wakeup can get prev
- * running on another CPU and we could rave with its RUNNING -> DEAD
+ * running on another CPU and we could race with its RUNNING -> DEAD
* transition, resulting in a double drop.
*/
prev_state = prev->state;
@@ -2720,7 +2720,8 @@ static struct rq *finish_task_switch(struct task_struct *prev)
break;
case TASK_PARKED:
- kthread_park_complete(prev);
+ if (!preempt)
+ kthread_park_complete(prev);
Yes, but this won't fix the race decribed by Kohli...
Plus this complicates the schedule() paths for the very special case, and to me
it seems that all this kthread_park/unpark logic needs some serious cleanups...
Not that I can suggest something better right now.
Oleg.
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