sched/all: Change all BUG_ON() instances in the scheduler to WARN_ON_ONCE()

There's no good reason to crash a user's system with a BUG_ON(),
chances are high that they'll never even see the crash message on
Xorg, and it won't make it into the syslog either.

By using a WARN_ON_ONCE() we at least give the user a chance to report
any bugs triggered here - instead of getting silent hangs.

None of these WARN_ON_ONCE()s are supposed to trigger, ever - so we ignore
cases where a NULL check is done via a BUG_ON() and we let a NULL
pointer through after a WARN_ON_ONCE().

There's one exception: WARN_ON_ONCE() arguments with side-effects,
such as locking - in this case we use the return value of the
WARN_ON_ONCE(), such as in:

 -       BUG_ON(!lock_task_sighand(p, &flags));
 +       if (WARN_ON_ONCE(!lock_task_sighand(p, &flags)))
 +               return;

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/YvSsKcAXISmshtHo@gmail.com

1 files changed, 13 insertions, 13 deletions

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0ab79d819a0d..962b169b05cf 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -310,7 +310,7 @@ static void dl_change_utilization(struct task_struct *p, u64 new_bw)
 {
 	struct rq *rq;
 
-	BUG_ON(p->dl.flags & SCHED_FLAG_SUGOV);
+	WARN_ON_ONCE(p->dl.flags & SCHED_FLAG_SUGOV);
 
 	if (task_on_rq_queued(p))
 		return;
@@ -607,7 +607,7 @@ static void enqueue_pushable_dl_task(struct rq *rq, struct task_struct *p)
 {
 	struct rb_node *leftmost;
 
-	BUG_ON(!RB_EMPTY_NODE(&p->pushable_dl_tasks));
+	WARN_ON_ONCE(!RB_EMPTY_NODE(&p->pushable_dl_tasks));
 
 	leftmost = rb_add_cached(&p->pushable_dl_tasks,
 				 &rq->dl.pushable_dl_tasks_root,
@@ -684,7 +684,7 @@ static struct rq *dl_task_offline_migration(struct rq *rq, struct task_struct *p
 			 * Failed to find any suitable CPU.
 			 * The task will never come back!
 			 */
-			BUG_ON(dl_bandwidth_enabled());
+			WARN_ON_ONCE(dl_bandwidth_enabled());
 
 			/*
 			 * If admission control is disabled we
@@ -830,7 +830,7 @@ static void replenish_dl_entity(struct sched_dl_entity *dl_se)
 	struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
 	struct rq *rq = rq_of_dl_rq(dl_rq);
 
-	BUG_ON(pi_of(dl_se)->dl_runtime <= 0);
+	WARN_ON_ONCE(pi_of(dl_se)->dl_runtime <= 0);
 
 	/*
 	 * This could be the case for a !-dl task that is boosted.
@@ -1616,7 +1616,7 @@ static void __enqueue_dl_entity(struct sched_dl_entity *dl_se)
 {
 	struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
 
-	BUG_ON(!RB_EMPTY_NODE(&dl_se->rb_node));
+	WARN_ON_ONCE(!RB_EMPTY_NODE(&dl_se->rb_node));
 
 	rb_add_cached(&dl_se->rb_node, &dl_rq->root, __dl_less);
 
@@ -1640,7 +1640,7 @@ static void __dequeue_dl_entity(struct sched_dl_entity *dl_se)
 static void
 enqueue_dl_entity(struct sched_dl_entity *dl_se, int flags)
 {
-	BUG_ON(on_dl_rq(dl_se));
+	WARN_ON_ONCE(on_dl_rq(dl_se));
 
 	update_stats_enqueue_dl(dl_rq_of_se(dl_se), dl_se, flags);
 
@@ -2017,7 +2017,7 @@ static struct task_struct *pick_task_dl(struct rq *rq)
 		return NULL;
 
 	dl_se = pick_next_dl_entity(dl_rq);
-	BUG_ON(!dl_se);
+	WARN_ON_ONCE(!dl_se);
 	p = dl_task_of(dl_se);
 
 	return p;
@@ -2277,12 +2277,12 @@ static struct task_struct *pick_next_pushable_dl_task(struct rq *rq)
 
 	p = __node_2_pdl(rb_first_cached(&rq->dl.pushable_dl_tasks_root));
 
-	BUG_ON(rq->cpu != task_cpu(p));
-	BUG_ON(task_current(rq, p));
-	BUG_ON(p->nr_cpus_allowed <= 1);
+	WARN_ON_ONCE(rq->cpu != task_cpu(p));
+	WARN_ON_ONCE(task_current(rq, p));
+	WARN_ON_ONCE(p->nr_cpus_allowed <= 1);
 
-	BUG_ON(!task_on_rq_queued(p));
-	BUG_ON(!dl_task(p));
+	WARN_ON_ONCE(!task_on_rq_queued(p));
+	WARN_ON_ONCE(!dl_task(p));
 
 	return p;
 }
@@ -2492,7 +2492,7 @@ static void set_cpus_allowed_dl(struct task_struct *p,
 	struct root_domain *src_rd;
 	struct rq *rq;
 
-	BUG_ON(!dl_task(p));
+	WARN_ON_ONCE(!dl_task(p));
 
 	rq = task_rq(p);
 	src_rd = rq->rd;