[PATCH 07/12] kthread: to_live_kthread() needs try_get_task_stack()

[Andy Lutomirski]

From: Oleg Nesterov 

get_task_struct(tsk) no longer pins tsk->stack so all users of
to_live_kthread() should do try_get_task_stack/put_task_stack to protect
"struct kthread" which lives on kthread's stack.

TODO: Kill to_live_kthread(), perhaps we can even kill "struct kthread" too,
and rework kthread_stop(), it can use task_work_add() to sync with the exiting
kernel thread.

Message-Id: <20160629180357.ga7...@redhat.com>
Signed-off-by: Oleg Nesterov 
Signed-off-by: Andy Lutomirski 
---
 kernel/kthread.c | 8 ++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 9ff173dca1ae..4ab4c3766a80 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -64,7 +64,7 @@ static inline struct kthread *to_kthread(struct task_struct 
*k)
 static struct kthread *to_live_kthread(struct task_struct *k)
 {
struct completion *vfork = ACCESS_ONCE(k->vfork_done);
-   if (likely(vfork))
+   if (likely(vfork) && try_get_task_stack(k))
return __to_kthread(vfork);
return NULL;
 }
@@ -425,8 +425,10 @@ void kthread_unpark(struct task_struct *k)
 {
struct kthread *kthread = to_live_kthread(k);
 
-   if (kthread)
+   if (kthread) {
__kthread_unpark(k, kthread);
+   put_task_stack(k);
+   }
 }
 EXPORT_SYMBOL_GPL(kthread_unpark);
 
@@ -455,6 +457,7 @@ int kthread_park(struct task_struct *k)
wait_for_completion(>parked);
}
}
+   put_task_stack(k);
ret = 0;
}
return ret;
@@ -490,6 +493,7 @@ int kthread_stop(struct task_struct *k)
__kthread_unpark(k, kthread);
wake_up_process(k);
wait_for_completion(>exited);
+   put_task_stack(k);
}
ret = k->exit_code;
put_task_struct(k);
-- 
2.7.4

[PATCH 07/12] kthread: to_live_kthread() needs try_get_task_stack()

[Andy Lutomirski]

From: Oleg Nesterov 

get_task_struct(tsk) no longer pins tsk->stack so all users of
to_live_kthread() should do try_get_task_stack/put_task_stack to protect
"struct kthread" which lives on kthread's stack.

TODO: Kill to_live_kthread(), perhaps we can even kill "struct kthread" too,
and rework kthread_stop(), it can use task_work_add() to sync with the exiting
kernel thread.

Message-Id: <20160629180357.ga7...@redhat.com>
Signed-off-by: Oleg Nesterov 
Signed-off-by: Andy Lutomirski 
---
 kernel/kthread.c | 8 ++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 9ff173dca1ae..4ab4c3766a80 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -64,7 +64,7 @@ static inline struct kthread *to_kthread(struct task_struct 
*k)
 static struct kthread *to_live_kthread(struct task_struct *k)
 {
struct completion *vfork = ACCESS_ONCE(k->vfork_done);
-   if (likely(vfork))
+   if (likely(vfork) && try_get_task_stack(k))
return __to_kthread(vfork);
return NULL;
 }
@@ -425,8 +425,10 @@ void kthread_unpark(struct task_struct *k)
 {
struct kthread *kthread = to_live_kthread(k);
 
-   if (kthread)
+   if (kthread) {
__kthread_unpark(k, kthread);
+   put_task_stack(k);
+   }
 }
 EXPORT_SYMBOL_GPL(kthread_unpark);
 
@@ -455,6 +457,7 @@ int kthread_park(struct task_struct *k)
wait_for_completion(>parked);
}
}
+   put_task_stack(k);
ret = 0;
}
return ret;
@@ -490,6 +493,7 @@ int kthread_stop(struct task_struct *k)
__kthread_unpark(k, kthread);
wake_up_process(k);
wait_for_completion(>exited);
+   put_task_stack(k);
}
ret = k->exit_code;
put_task_struct(k);
-- 
2.7.4