CPU hangs were reported while offlining/onlining CPUs on s390.
Analyzing the vmcore data shows `stop_one_cpu_nowait()` in `affine_move_task()`
can fail when racing with off-/on-lining resulting in a deadlock waiting for
the pending migration stop work completion which is never done.
Fix this by gracefully handling such condition.
Fixes: 9e81889c7648 ("sched: Fix affine_move_task() self-concurrency")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Bill Peters <wpeters@xxxxxxxxx>
Tested-by: Bill Peters <wpeters@xxxxxxxxx>
Signed-off-by: Daniel Vacek <neelx@xxxxxxxxxx>
---
kernel/sched/core.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f3951e4a55e5b..40a3c9ff74077 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2871,8 +2871,25 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
preempt_disable();
task_rq_unlock(rq, p, rf);
if (!stop_pending) {
- stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
- &pending->arg, &pending->stop_work);
+ stop_pending =
+ stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
+ &pending->arg, &pending->stop_work);
+ /*
+ * The state resulting in this failure is not expected
+ * at this point. At least report a WARNING to be able
+ * to panic and further debug if reproduced.
+ */
+ if (WARN_ON(!stop_pending)) {
+ /*
+ * Then try to handle the failure gracefully
+ * to prevent the deadlock a few lines later.
+ */
+ rq = task_rq_lock(p, rf);
+ pending->stop_pending = false;
+ p->migration_pending = NULL;
+ task_rq_unlock(rq, p, rf);
+ complete_all(&pending->done);
+ }
}
preempt_enable();
--
2.43.0
