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Subject[PATCH 2/2] kthread: kill task_get_live_kthread()
task_get_live_kthread() looks confusing and unneeded. It does
get_task_struct() but only kthread_stop() needs this, it can be
called even if the calller doesn't have a reference when we know
that this kthread can't exit until we do kthread_stop().

kthread_park() and kthread_unpark() do not need get_task_struct(),
the callers already have the reference. And it can not help if we
can race with the exiting kthread anyway, kthread_park() can hang
forever in this case.

Change kthread_park() and kthread_unpark() to use to_live_kthread(),
change kthread_stop() to do get_task_struct() by hand and remove
task_get_live_kthread().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/kthread.c | 20 +++++++-------------
1 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index fa4a013..d345f4e 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -324,12 +324,6 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
return p;
}

-static struct kthread *task_get_live_kthread(struct task_struct *k)
-{
- get_task_struct(k);
- return to_live_kthread(k);
-}
-
/**
* kthread_unpark - unpark a thread created by kthread_create().
* @k: thread created by kthread_create().
@@ -340,7 +334,7 @@ static struct kthread *task_get_live_kthread(struct task_struct *k)
*/
void kthread_unpark(struct task_struct *k)
{
- struct kthread *kthread = task_get_live_kthread(k);
+ struct kthread *kthread = to_live_kthread(k);

if (kthread) {
clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
@@ -356,7 +350,6 @@ void kthread_unpark(struct task_struct *k)
wake_up_process(k);
}
}
- put_task_struct(k);
}

/**
@@ -373,7 +366,7 @@ void kthread_unpark(struct task_struct *k)
*/
int kthread_park(struct task_struct *k)
{
- struct kthread *kthread = task_get_live_kthread(k);
+ struct kthread *kthread = to_live_kthread(k);
int ret = -ENOSYS;

if (kthread) {
@@ -386,7 +379,6 @@ int kthread_park(struct task_struct *k)
}
ret = 0;
}
- put_task_struct(k);
return ret;
}

@@ -407,10 +399,13 @@ int kthread_park(struct task_struct *k)
*/
int kthread_stop(struct task_struct *k)
{
- struct kthread *kthread = task_get_live_kthread(k);
+ struct kthread *kthread;
int ret;

trace_sched_kthread_stop(k);
+
+ get_task_struct(k);
+ kthread = to_live_kthread(k);
if (kthread) {
set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
@@ -418,10 +413,9 @@ int kthread_stop(struct task_struct *k)
wait_for_completion(&kthread->exited);
}
ret = k->exit_code;
-
put_task_struct(k);
- trace_sched_kthread_stop_ret(ret);

+ trace_sched_kthread_stop_ret(ret);
return ret;
}
EXPORT_SYMBOL(kthread_stop);
--
1.5.5.1


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