[PATCH 1/6] sched: Constrain locks in sched_submit_work()

Peter Zijlstra
2023-08-15T11:18:06Z

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) <peterz@infradead.org>
---
kernel/sched/core.c | 9 +++++++++
1 file changed, 9 insertions(+)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6737,11 +6737,18 @@ 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
@@ -6766,6 +6773,8 @@ static inline void sched_submit_work(str
* 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)