[PATCH] siox: don't create a thread without starting it

From: Uwe Kleine-KÃnig
Date: Thu Jun 28 2018 - 03:57:57 EST


When a siox master device is registered a kthread is created that is
only started when triggered by userspace. So this thread might be in
TASK_UNINTERRUPTIBLE state for long and trigger a warning

[ 241.130465] INFO: task siox-0:626 blocked for more than 120 seconds.

with the respective debug settings enabled. It might be right to put an
unstarted thread to TASK_IDLE (in kernel/kthread.c:kthread()) instead,
but independant of this discussion it is cleaner for
siox_master_register() to start the thread immediately. The effect is
that it enters its own waiting state and then stays in state TASK_IDLE
which doesn't trigger the above warning.

As siox_poll_thread() uses some variables of the device the
initialisation of these is moved before thread creation.

Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Uwe Kleine-KÃnig <u.kleine-koenig@xxxxxxxxxxxxxx>
---
Hello,

this is the same patch as before with an updated commit log. I added
Peter's ack anyhow assuming my text isn't too bad to make him withdraw
it.

I think this issue isn't critical as the machine works fine otherwise,
so applying it for 4.18-rc isn't necessary.
(OTOH it's an SMP machine so the tests might not have noticed one blocked
CPU, didn't test this.)

Greg, you applied the initial patches creating drivers/siox. I assume
you will continue to apply siox patches and tell if I should search a
different path for these.

Best regards
Uwe

drivers/siox/siox-core.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/siox/siox-core.c b/drivers/siox/siox-core.c
index 16590dfaafa4..cef307c0399c 100644
--- a/drivers/siox/siox-core.c
+++ b/drivers/siox/siox-core.c
@@ -715,17 +715,17 @@ int siox_master_register(struct siox_master *smaster)

dev_set_name(&smaster->dev, "siox-%d", smaster->busno);

+ mutex_init(&smaster->lock);
+ INIT_LIST_HEAD(&smaster->devices);
+
smaster->last_poll = jiffies;
- smaster->poll_thread = kthread_create(siox_poll_thread, smaster,
- "siox-%d", smaster->busno);
+ smaster->poll_thread = kthread_run(siox_poll_thread, smaster,
+ "siox-%d", smaster->busno);
if (IS_ERR(smaster->poll_thread)) {
smaster->active = 0;
return PTR_ERR(smaster->poll_thread);
}

- mutex_init(&smaster->lock);
- INIT_LIST_HEAD(&smaster->devices);
-
ret = device_add(&smaster->dev);
if (ret)
kthread_stop(smaster->poll_thread);
--
2.18.0