Having a stable wchan means the process must be blocked and for it to
stay that way while performing stack unwinding.
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
include/linux/sched.h | 1 +
kernel/sched/core.c | 16 ++++++++++++++++
2 files changed, 17 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 39039ce8ac4c..0c8185089e20 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2137,6 +2137,7 @@ static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
#endif /* CONFIG_SMP */
extern bool sched_task_on_rq(struct task_struct *p);
+extern unsigned long sched_task_get_wchan(struct task_struct *p);
/*
* In order to reduce various lock holder preemption latencies provide an
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1bba4128a3e6..4a30455e1ff5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1962,6 +1962,22 @@ bool sched_task_on_rq(struct task_struct *p)
return task_on_rq_queued(p);
}
+unsigned long sched_task_get_wchan(struct task_struct *p)
+{
+ unsigned int state;
+ unsigned long ip = 0;
+
+ /* Only get wchan if task is blocked and we can keep it that way. */
+ raw_spin_lock_irq(&p->pi_lock);
+ state = READ_ONCE(p->__state);
+ smp_rmb(); /* see try_to_wake_up() */
+ if (state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq)
+ ip = get_wchan(p);
+ raw_spin_unlock_irq(&p->pi_lock);
+
+ return ip;
+}
+
static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
{
if (!(flags & ENQUEUE_NOCLOCK))
--
2.30.2
