sched: Constrain locks in sched_submit_work()

Even though sched_submit_work() is ran from preemptible context,
it is discouraged to have it use blocking locks due to the recursion
potential.

Enforce this.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: Peter Zijlstra

kernel/sched/core.c

@@ -6720,11 +6720,18 @@ void __noreturn do_task_dead(void)
 
 static inline void sched_submit_work(struct task_struct *tsk)
 {
+	static DEFINE_WAIT_OVERRIDE_MAP(sched_map, LD_WAIT_CONFIG);
 	unsigned int task_flags;
 
 	if (task_is_running(tsk))
 		return;
 
+	/*
+	 * Establish LD_WAIT_CONFIG context to ensure none of the code called
+	 * will use a blocking primitive -- which would lead to recursion.
+	 */
+	lock_map_acquire_try(&sched_map);
+
 	task_flags = tsk->flags;
 	/*
 	 * If a worker goes to sleep, notify and ask workqueue whether it
@@ -6749,6 +6756,8 @@ static inline void sched_submit_work(struct task_struct *tsk)
 	 * make sure to submit it to avoid deadlocks.
 	 */
 	blk_flush_plug(tsk->plug, true);
+
+	lock_map_release(&sched_map);
 }
 
 static void sched_update_worker(struct task_struct *tsk)