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, 5 insertions, 5 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 914096c5b1ae..28f10dccd194 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2600,7 +2600,7 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
 	if (!join)
 		return;
 
-	BUG_ON(irqs_disabled());
+	WARN_ON_ONCE(irqs_disabled());
 	double_lock_irq(&my_grp->lock, &grp->lock);
 
 	for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
@@ -7279,7 +7279,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
 		return;
 
 	find_matching_se(&se, &pse);
-	BUG_ON(!pse);
+	WARN_ON_ONCE(!pse);
 
 	cse_is_idle = se_is_idle(se);
 	pse_is_idle = se_is_idle(pse);
@@ -8159,7 +8159,7 @@ static void attach_task(struct rq *rq, struct task_struct *p)
 {
 	lockdep_assert_rq_held(rq);
 
-	BUG_ON(task_rq(p) != rq);
+	WARN_ON_ONCE(task_rq(p) != rq);
 	activate_task(rq, p, ENQUEUE_NOCLOCK);
 	check_preempt_curr(rq, p, 0);
 }
@@ -10134,7 +10134,7 @@ redo:
 		goto out_balanced;
 	}
 
-	BUG_ON(busiest == env.dst_rq);
+	WARN_ON_ONCE(busiest == env.dst_rq);
 
 	schedstat_add(sd->lb_imbalance[idle], env.imbalance);
 
@@ -10430,7 +10430,7 @@ static int active_load_balance_cpu_stop(void *data)
 	 * we need to fix it. Originally reported by
 	 * Bjorn Helgaas on a 128-CPU setup.
 	 */
-	BUG_ON(busiest_rq == target_rq);
+	WARN_ON_ONCE(busiest_rq == target_rq);
 
 	/* Search for an sd spanning us and the target CPU. */
 	rcu_read_lock();