Hi ,
We can also fix below race by smpboot code as well:
@@ -109,7 +109,6 @@ static int smpboot_thread_fn(void *data)
struct smp_hotplug_thread *ht = td->ht;
while (1) {
- set_current_state(TASK_INTERRUPTIBLE);
preempt_disable();
if (kthread_should_stop()) {
__set_current_state(TASK_RUNNING);
@@ -157,6 +156,7 @@ static int smpboot_thread_fn(void *data)
if (!ht->thread_should_run(td->cpu)) {
preempt_enable_no_resched();
+ set_current_state(TASK_INTERRUPTIBLE);
schedule();
} else {
__set_current_state(TASK_RUNNING);
Please suggest if this approach is better.
Regards
Gaurav
On 4/24/2018 2:58 PM, Gaurav Kohli wrote:
The control cpu thread which initiates hotplug calls kthread_park()
for hotplug thread and sets KTHREAD_SHOULD_PARK. After this control
thread wakes up the hotplug thread. There is a chance that wakeup
code sees the hotplug thread (running on AP core) in INTERRUPTIBLE
state, but sets its state to RUNNING after hotplug thread has entered
kthread_parkme() and changed its state to TASK_PARKED. This can result
in panic later on in kthread_unpark(), as it sees KTHREAD_IS_PARKED
flag set but fails to rebind the kthread, due to it being not in
TASK_PARKED state. Fix this, by serializing wakeup state change,
against state change before parking the kthread.
Below is the possible race:
Control thread Hotplug Thread
kthread_park()
set KTHREAD_SHOULD_PARK
smpboot_thread_fn
set_current_state(TASK_INTERRUPTIBLE);
kthread_parkme
wake_up_process()
raw_spin_lock_irqsave(&p->pi_lock, flags);
if (!(p->state & state)) -> this will fail
goto out;
__kthread_parkme
__set_current_state(TASK_PARKED);
if (p->on_rq && ttwu_remote(p, wake_flags))
ttwu_remote()
p->state = TASK_RUNNING;
schedule();
So to avoid this race, take pi_lock to serial state changes.
Suggested-by: Pavankumar Kondeti <pkondeti@xxxxxxxxxxxxxx>
Co-developed-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
Signed-off-by: Gaurav Kohli <gkohli@xxxxxxxxxxxxxx>
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 1650578..514b232 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -121,7 +121,9 @@ static int smpboot_thread_fn(void *data)
}
if (kthread_should_park()) {
+ raw_spin_lock(¤t->pi_lock);
__set_current_state(TASK_RUNNING);
+ raw_spin_unlock(¤t->pi_lock);
preempt_enable();
if (ht->park && td->status == HP_THREAD_ACTIVE) {
BUG_ON(td->cpu != smp_processor_id());
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
--
To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
