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kthread: kill task_get_live_kthread()

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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>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2013-04-29 15:05:12 -07:00 committed by Linus Torvalds
parent 4ecdafc808
commit b5c5442bb6
1 changed files with 7 additions and 13 deletions
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20
kernel/kthread.c
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@ -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);
}
static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
{
clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
@ -356,11 +350,10 @@ static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
*/
void kthread_unpark(struct task_struct *k)
{
struct kthread *kthread = task_get_live_kthread(k);
struct kthread *kthread = to_live_kthread(k);
if (kthread)
__kthread_unpark(k, kthread);
put_task_struct(k);
}
/**
@ -377,7 +370,7 @@ 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) {
@ -390,7 +383,6 @@ int kthread_park(struct task_struct *k)
}
ret = 0;
}
put_task_struct(k);
return ret;
}
@ -411,10 +403,13 @@ 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);
__kthread_unpark(k, kthread);
@ -422,10 +417,9 @@ 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);