The scheduler has this special SCHED_WARN() facility that
depends on CONFIG_SCHED_DEBUG.

Since CONFIG_SCHED_DEBUG is getting removed, convert
SCHED_WARN() to WARN_ON_ONCE().

Note that the warning output isn't 100% equivalent:

   #define SCHED_WARN_ON(x)      WARN_ONCE(x, #x)

Because SCHED_WARN_ON() would output the 'x' condition
as well, while WARN_ONCE() will only show a backtrace.

Hopefully these are rare enough to not really matter.

If it does, we should probably introduce a new WARN_ON()
variant that outputs the condition in stringified form,
or improve WARN_ON() itself.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c       | 24 ++++++++++++------------
 kernel/sched/core_sched.c |  2 +-
 kernel/sched/deadline.c   | 12 ++++++------
 kernel/sched/ext.c        |  2 +-
 kernel/sched/fair.c       | 58 +++++++++++++++++++++++++++++-----------------------------
 kernel/sched/rt.c         |  2 +-
 kernel/sched/sched.h      | 16 +++++-----------
 kernel/sched/stats.h      |  2 +-
 8 files changed, 56 insertions(+), 62 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 03d7b63dc3e5..2da197b2968b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -801,7 +801,7 @@ void update_rq_clock(struct rq *rq)
 
 #ifdef CONFIG_SCHED_DEBUG
 	if (sched_feat(WARN_DOUBLE_CLOCK))
-		SCHED_WARN_ON(rq->clock_update_flags & RQCF_UPDATED);
+		WARN_ON_ONCE(rq->clock_update_flags & RQCF_UPDATED);
 	rq->clock_update_flags |= RQCF_UPDATED;
 #endif
 	clock = sched_clock_cpu(cpu_of(rq));
@@ -1719,7 +1719,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
 
 	bucket = &uc_rq->bucket[uc_se->bucket_id];
 
-	SCHED_WARN_ON(!bucket->tasks);
+	WARN_ON_ONCE(!bucket->tasks);
 	if (likely(bucket->tasks))
 		bucket->tasks--;
 
@@ -1739,7 +1739,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
 	 * Defensive programming: this should never happen. If it happens,
 	 * e.g. due to future modification, warn and fix up the expected value.
 	 */
-	SCHED_WARN_ON(bucket->value > rq_clamp);
+	WARN_ON_ONCE(bucket->value > rq_clamp);
 	if (bucket->value >= rq_clamp) {
 		bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
 		uclamp_rq_set(rq, clamp_id, bkt_clamp);
@@ -2121,7 +2121,7 @@ void activate_task(struct rq *rq, struct task_struct *p, int flags)
 
 void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
 {
-	SCHED_WARN_ON(flags & DEQUEUE_SLEEP);
+	WARN_ON_ONCE(flags & DEQUEUE_SLEEP);
 
 	WRITE_ONCE(p->on_rq, TASK_ON_RQ_MIGRATING);
 	ASSERT_EXCLUSIVE_WRITER(p->on_rq);
@@ -2726,7 +2726,7 @@ __do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
 	 * XXX do further audits, this smells like something putrid.
 	 */
 	if (ctx->flags & SCA_MIGRATE_DISABLE)
-		SCHED_WARN_ON(!p->on_cpu);
+		WARN_ON_ONCE(!p->on_cpu);
 	else
 		lockdep_assert_held(&p->pi_lock);
 
@@ -4195,7 +4195,7 @@ int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 		 *  - we're serialized against set_special_state() by virtue of
 		 *    it disabling IRQs (this allows not taking ->pi_lock).
 		 */
-		SCHED_WARN_ON(p->se.sched_delayed);
+		WARN_ON_ONCE(p->se.sched_delayed);
 		if (!ttwu_state_match(p, state, &success))
 			goto out;
 
@@ -4489,7 +4489,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 	INIT_LIST_HEAD(&p->se.group_node);
 
 	/* A delayed task cannot be in clone(). */
-	SCHED_WARN_ON(p->se.sched_delayed);
+	WARN_ON_ONCE(p->se.sched_delayed);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	p->se.cfs_rq			= NULL;
@@ -5745,7 +5745,7 @@ static void sched_tick_remote(struct work_struct *work)
 			 * we are always sure that there is no proxy (only a
 			 * single task is running).
 			 */
-			SCHED_WARN_ON(rq->curr != rq->donor);
+			WARN_ON_ONCE(rq->curr != rq->donor);
 			update_rq_clock(rq);
 
 			if (!is_idle_task(curr)) {
@@ -5965,7 +5965,7 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt)
 		preempt_count_set(PREEMPT_DISABLED);
 	}
 	rcu_sleep_check();
-	SCHED_WARN_ON(ct_state() == CT_STATE_USER);
+	WARN_ON_ONCE(ct_state() == CT_STATE_USER);
 
 	profile_hit(SCHED_PROFILING, __builtin_return_address(0));
 
@@ -6811,7 +6811,7 @@ static inline void sched_submit_work(struct task_struct *tsk)
 	 * deadlock if the callback attempts to acquire a lock which is
 	 * already acquired.
 	 */
-	SCHED_WARN_ON(current->__state & TASK_RTLOCK_WAIT);
+	WARN_ON_ONCE(current->__state & TASK_RTLOCK_WAIT);
 
 	/*
 	 * If we are going to sleep and we have plugged IO queued,
@@ -9202,7 +9202,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
 	unsigned int clamps;
 
 	lockdep_assert_held(&uclamp_mutex);
-	SCHED_WARN_ON(!rcu_read_lock_held());
+	WARN_ON_ONCE(!rcu_read_lock_held());
 
 	css_for_each_descendant_pre(css, top_css) {
 		uc_parent = css_tg(css)->parent
@@ -10537,7 +10537,7 @@ static void task_mm_cid_work(struct callback_head *work)
 	struct mm_struct *mm;
 	int weight, cpu;
 
-	SCHED_WARN_ON(t != container_of(work, struct task_struct, cid_work));
+	WARN_ON_ONCE(t != container_of(work, struct task_struct, cid_work));
 
 	work->next = work;	/* Prevent double-add */
 	if (t->flags & PF_EXITING)
diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c
index 1ef98a93eb1d..c4606ca89210 100644
--- a/kernel/sched/core_sched.c
+++ b/kernel/sched/core_sched.c
@@ -65,7 +65,7 @@ static unsigned long sched_core_update_cookie(struct task_struct *p,
 	 * a cookie until after we've removed it, we must have core scheduling
 	 * enabled here.
 	 */
-	SCHED_WARN_ON((p->core_cookie || cookie) && !sched_core_enabled(rq));
+	WARN_ON_ONCE((p->core_cookie || cookie) && !sched_core_enabled(rq));
 
 	if (sched_core_enqueued(p))
 		sched_core_dequeue(rq, p, DEQUEUE_SAVE);
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index ff4df16b5186..b18c80272f86 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -249,8 +249,8 @@ void __add_running_bw(u64 dl_bw, struct dl_rq *dl_rq)
 
 	lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
 	dl_rq->running_bw += dl_bw;
-	SCHED_WARN_ON(dl_rq->running_bw < old); /* overflow */
-	SCHED_WARN_ON(dl_rq->running_bw > dl_rq->this_bw);
+	WARN_ON_ONCE(dl_rq->running_bw < old); /* overflow */
+	WARN_ON_ONCE(dl_rq->running_bw > dl_rq->this_bw);
 	/* kick cpufreq (see the comment in kernel/sched/sched.h). */
 	cpufreq_update_util(rq_of_dl_rq(dl_rq), 0);
 }
@@ -262,7 +262,7 @@ void __sub_running_bw(u64 dl_bw, struct dl_rq *dl_rq)
 
 	lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
 	dl_rq->running_bw -= dl_bw;
-	SCHED_WARN_ON(dl_rq->running_bw > old); /* underflow */
+	WARN_ON_ONCE(dl_rq->running_bw > old); /* underflow */
 	if (dl_rq->running_bw > old)
 		dl_rq->running_bw = 0;
 	/* kick cpufreq (see the comment in kernel/sched/sched.h). */
@@ -276,7 +276,7 @@ void __add_rq_bw(u64 dl_bw, struct dl_rq *dl_rq)
 
 	lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
 	dl_rq->this_bw += dl_bw;
-	SCHED_WARN_ON(dl_rq->this_bw < old); /* overflow */
+	WARN_ON_ONCE(dl_rq->this_bw < old); /* overflow */
 }
 
 static inline
@@ -286,10 +286,10 @@ void __sub_rq_bw(u64 dl_bw, struct dl_rq *dl_rq)
 
 	lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
 	dl_rq->this_bw -= dl_bw;
-	SCHED_WARN_ON(dl_rq->this_bw > old); /* underflow */
+	WARN_ON_ONCE(dl_rq->this_bw > old); /* underflow */
 	if (dl_rq->this_bw > old)
 		dl_rq->this_bw = 0;
-	SCHED_WARN_ON(dl_rq->running_bw > dl_rq->this_bw);
+	WARN_ON_ONCE(dl_rq->running_bw > dl_rq->this_bw);
 }
 
 static inline
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 0f1da199cfc7..953a5b9ec0cd 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2341,7 +2341,7 @@ static bool task_can_run_on_remote_rq(struct task_struct *p, struct rq *rq,
 {
 	int cpu = cpu_of(rq);
 
-	SCHED_WARN_ON(task_cpu(p) == cpu);
+	WARN_ON_ONCE(task_cpu(p) == cpu);
 
 	/*
 	 * If @p has migration disabled, @p->cpus_ptr is updated to contain only
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9dafb374d76d..89609ebd4904 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -399,7 +399,7 @@ static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 
 static inline void assert_list_leaf_cfs_rq(struct rq *rq)
 {
-	SCHED_WARN_ON(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list);
+	WARN_ON_ONCE(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list);
 }
 
 /* Iterate through all leaf cfs_rq's on a runqueue */
@@ -696,7 +696,7 @@ static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	s64 vlag, limit;
 
-	SCHED_WARN_ON(!se->on_rq);
+	WARN_ON_ONCE(!se->on_rq);
 
 	vlag = avg_vruntime(cfs_rq) - se->vruntime;
 	limit = calc_delta_fair(max_t(u64, 2*se->slice, TICK_NSEC), se);
@@ -3317,7 +3317,7 @@ static void task_numa_work(struct callback_head *work)
 	bool vma_pids_skipped;
 	bool vma_pids_forced = false;
 
-	SCHED_WARN_ON(p != container_of(work, struct task_struct, numa_work));
+	WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work));
 
 	work->next = work;
 	/*
@@ -4036,7 +4036,7 @@ static inline bool load_avg_is_decayed(struct sched_avg *sa)
 	 * Make sure that rounding and/or propagation of PELT values never
 	 * break this.
 	 */
-	SCHED_WARN_ON(sa->load_avg ||
+	WARN_ON_ONCE(sa->load_avg ||
 		      sa->util_avg ||
 		      sa->runnable_avg);
 
@@ -5460,7 +5460,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	clear_buddies(cfs_rq, se);
 
 	if (flags & DEQUEUE_DELAYED) {
-		SCHED_WARN_ON(!se->sched_delayed);
+		WARN_ON_ONCE(!se->sched_delayed);
 	} else {
 		bool delay = sleep;
 		/*
@@ -5470,7 +5470,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 		if (flags & DEQUEUE_SPECIAL)
 			delay = false;
 
-		SCHED_WARN_ON(delay && se->sched_delayed);
+		WARN_ON_ONCE(delay && se->sched_delayed);
 
 		if (sched_feat(DELAY_DEQUEUE) && delay &&
 		    !entity_eligible(cfs_rq, se)) {
@@ -5551,7 +5551,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 	}
 
 	update_stats_curr_start(cfs_rq, se);
-	SCHED_WARN_ON(cfs_rq->curr);
+	WARN_ON_ONCE(cfs_rq->curr);
 	cfs_rq->curr = se;
 
 	/*
@@ -5592,7 +5592,7 @@ pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq)
 	if (sched_feat(PICK_BUDDY) &&
 	    cfs_rq->next && entity_eligible(cfs_rq, cfs_rq->next)) {
 		/* ->next will never be delayed */
-		SCHED_WARN_ON(cfs_rq->next->sched_delayed);
+		WARN_ON_ONCE(cfs_rq->next->sched_delayed);
 		return cfs_rq->next;
 	}
 
@@ -5628,7 +5628,7 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
 		/* in !on_rq case, update occurred at dequeue */
 		update_load_avg(cfs_rq, prev, 0);
 	}
-	SCHED_WARN_ON(cfs_rq->curr != prev);
+	WARN_ON_ONCE(cfs_rq->curr != prev);
 	cfs_rq->curr = NULL;
 }
 
@@ -5851,7 +5851,7 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
 
 			cfs_rq->throttled_clock_self = 0;
 
-			if (SCHED_WARN_ON((s64)delta < 0))
+			if (WARN_ON_ONCE((s64)delta < 0))
 				delta = 0;
 
 			cfs_rq->throttled_clock_self_time += delta;
@@ -5871,7 +5871,7 @@ static int tg_throttle_down(struct task_group *tg, void *data)
 		cfs_rq->throttled_clock_pelt = rq_clock_pelt(rq);
 		list_del_leaf_cfs_rq(cfs_rq);
 
-		SCHED_WARN_ON(cfs_rq->throttled_clock_self);
+		WARN_ON_ONCE(cfs_rq->throttled_clock_self);
 		if (cfs_rq->nr_queued)
 			cfs_rq->throttled_clock_self = rq_clock(rq);
 	}
@@ -5980,7 +5980,7 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
 	 * throttled-list.  rq->lock protects completion.
 	 */
 	cfs_rq->throttled = 1;
-	SCHED_WARN_ON(cfs_rq->throttled_clock);
+	WARN_ON_ONCE(cfs_rq->throttled_clock);
 	if (cfs_rq->nr_queued)
 		cfs_rq->throttled_clock = rq_clock(rq);
 	return true;
@@ -6136,7 +6136,7 @@ static inline void __unthrottle_cfs_rq_async(struct cfs_rq *cfs_rq)
 	}
 
 	/* Already enqueued */
-	if (SCHED_WARN_ON(!list_empty(&cfs_rq->throttled_csd_list)))
+	if (WARN_ON_ONCE(!list_empty(&cfs_rq->throttled_csd_list)))
 		return;
 
 	first = list_empty(&rq->cfsb_csd_list);
@@ -6155,7 +6155,7 @@ static void unthrottle_cfs_rq_async(struct cfs_rq *cfs_rq)
 {
 	lockdep_assert_rq_held(rq_of(cfs_rq));
 
-	if (SCHED_WARN_ON(!cfs_rq_throttled(cfs_rq) ||
+	if (WARN_ON_ONCE(!cfs_rq_throttled(cfs_rq) ||
 	    cfs_rq->runtime_remaining <= 0))
 		return;
 
@@ -6191,7 +6191,7 @@ static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b)
 			goto next;
 
 		/* By the above checks, this should never be true */
-		SCHED_WARN_ON(cfs_rq->runtime_remaining > 0);
+		WARN_ON_ONCE(cfs_rq->runtime_remaining > 0);
 
 		raw_spin_lock(&cfs_b->lock);
 		runtime = -cfs_rq->runtime_remaining + 1;
@@ -6212,7 +6212,7 @@ static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b)
 				 * We currently only expect to be unthrottling
 				 * a single cfs_rq locally.
 				 */
-				SCHED_WARN_ON(!list_empty(&local_unthrottle));
+				WARN_ON_ONCE(!list_empty(&local_unthrottle));
 				list_add_tail(&cfs_rq->throttled_csd_list,
 					      &local_unthrottle);
 			}
@@ -6237,7 +6237,7 @@ static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b)
 
 		rq_unlock_irqrestore(rq, &rf);
 	}
-	SCHED_WARN_ON(!list_empty(&local_unthrottle));
+	WARN_ON_ONCE(!list_empty(&local_unthrottle));
 
 	rcu_read_unlock();
 
@@ -6789,7 +6789,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
 {
 	struct sched_entity *se = &p->se;
 
-	SCHED_WARN_ON(task_rq(p) != rq);
+	WARN_ON_ONCE(task_rq(p) != rq);
 
 	if (rq->cfs.h_nr_queued > 1) {
 		u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
@@ -6900,8 +6900,8 @@ requeue_delayed_entity(struct sched_entity *se)
 	 * Because a delayed entity is one that is still on
 	 * the runqueue competing until elegibility.
 	 */
-	SCHED_WARN_ON(!se->sched_delayed);
-	SCHED_WARN_ON(!se->on_rq);
+	WARN_ON_ONCE(!se->sched_delayed);
+	WARN_ON_ONCE(!se->on_rq);
 
 	if (sched_feat(DELAY_ZERO)) {
 		update_entity_lag(cfs_rq, se);
@@ -7161,8 +7161,8 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
 		rq->next_balance = jiffies;
 
 	if (p && task_delayed) {
-		SCHED_WARN_ON(!task_sleep);
-		SCHED_WARN_ON(p->on_rq != 1);
+		WARN_ON_ONCE(!task_sleep);
+		WARN_ON_ONCE(p->on_rq != 1);
 
 		/* Fix-up what dequeue_task_fair() skipped */
 		hrtick_update(rq);
@@ -8740,7 +8740,7 @@ static inline void set_task_max_allowed_capacity(struct task_struct *p) {}
 static void set_next_buddy(struct sched_entity *se)
 {
 	for_each_sched_entity(se) {
-		if (SCHED_WARN_ON(!se->on_rq))
+		if (WARN_ON_ONCE(!se->on_rq))
 			return;
 		if (se_is_idle(se))
 			return;
@@ -12484,7 +12484,7 @@ static void set_cpu_sd_state_busy(int cpu)
 
 void nohz_balance_exit_idle(struct rq *rq)
 {
-	SCHED_WARN_ON(rq != this_rq());
+	WARN_ON_ONCE(rq != this_rq());
 
 	if (likely(!rq->nohz_tick_stopped))
 		return;
@@ -12520,7 +12520,7 @@ void nohz_balance_enter_idle(int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);
 
-	SCHED_WARN_ON(cpu != smp_processor_id());
+	WARN_ON_ONCE(cpu != smp_processor_id());
 
 	/* If this CPU is going down, then nothing needs to be done: */
 	if (!cpu_active(cpu))
@@ -12603,7 +12603,7 @@ static void _nohz_idle_balance(struct rq *this_rq, unsigned int flags)
 	int balance_cpu;
 	struct rq *rq;
 
-	SCHED_WARN_ON((flags & NOHZ_KICK_MASK) == NOHZ_BALANCE_KICK);
+	WARN_ON_ONCE((flags & NOHZ_KICK_MASK) == NOHZ_BALANCE_KICK);
 
 	/*
 	 * We assume there will be no idle load after this update and clear
@@ -13043,7 +13043,7 @@ bool cfs_prio_less(const struct task_struct *a, const struct task_struct *b,
 	struct cfs_rq *cfs_rqb;
 	s64 delta;
 
-	SCHED_WARN_ON(task_rq(b)->core != rq->core);
+	WARN_ON_ONCE(task_rq(b)->core != rq->core);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	/*
@@ -13246,7 +13246,7 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
 
 static void switched_to_fair(struct rq *rq, struct task_struct *p)
 {
-	SCHED_WARN_ON(p->se.sched_delayed);
+	WARN_ON_ONCE(p->se.sched_delayed);
 
 	attach_task_cfs_rq(p);
 
@@ -13281,7 +13281,7 @@ static void __set_next_task_fair(struct rq *rq, struct task_struct *p, bool firs
 	if (!first)
 		return;
 
-	SCHED_WARN_ON(se->sched_delayed);
+	WARN_ON_ONCE(se->sched_delayed);
 
 	if (hrtick_enabled_fair(rq))
 		hrtick_start_fair(rq, p);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4b8e33c615b1..926281ac3ac0 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1713,7 +1713,7 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rt_rq *rt_rq)
 	BUG_ON(idx >= MAX_RT_PRIO);
 
 	queue = array->queue + idx;
-	if (SCHED_WARN_ON(list_empty(queue)))
+	if (WARN_ON_ONCE(list_empty(queue)))
 		return NULL;
 	next = list_entry(queue->next, struct sched_rt_entity, run_list);
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0212a0c5534a..189f7b033dab 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -91,12 +91,6 @@ struct cpuidle_state;
 #include "cpupri.h"
 #include "cpudeadline.h"
 
-#ifdef CONFIG_SCHED_DEBUG
-# define SCHED_WARN_ON(x)      WARN_ONCE(x, #x)
-#else
-# define SCHED_WARN_ON(x)      ({ (void)(x), 0; })
-#endif
-
 /* task_struct::on_rq states: */
 #define TASK_ON_RQ_QUEUED	1
 #define TASK_ON_RQ_MIGRATING	2
@@ -1571,7 +1565,7 @@ static inline void update_idle_core(struct rq *rq) { }
 
 static inline struct task_struct *task_of(struct sched_entity *se)
 {
-	SCHED_WARN_ON(!entity_is_task(se));
+	WARN_ON_ONCE(!entity_is_task(se));
 	return container_of(se, struct task_struct, se);
 }
 
@@ -1652,7 +1646,7 @@ static inline void assert_clock_updated(struct rq *rq)
 	 * The only reason for not seeing a clock update since the
 	 * last rq_pin_lock() is if we're currently skipping updates.
 	 */
-	SCHED_WARN_ON(rq->clock_update_flags < RQCF_ACT_SKIP);
+	WARN_ON_ONCE(rq->clock_update_flags < RQCF_ACT_SKIP);
 }
 
 static inline u64 rq_clock(struct rq *rq)
@@ -1699,7 +1693,7 @@ static inline void rq_clock_cancel_skipupdate(struct rq *rq)
 static inline void rq_clock_start_loop_update(struct rq *rq)
 {
 	lockdep_assert_rq_held(rq);
-	SCHED_WARN_ON(rq->clock_update_flags & RQCF_ACT_SKIP);
+	WARN_ON_ONCE(rq->clock_update_flags & RQCF_ACT_SKIP);
 	rq->clock_update_flags |= RQCF_ACT_SKIP;
 }
 
@@ -1774,7 +1768,7 @@ static inline void rq_pin_lock(struct rq *rq, struct rq_flags *rf)
 	rq->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
 	rf->clock_update_flags = 0;
 # ifdef CONFIG_SMP
-	SCHED_WARN_ON(rq->balance_callback && rq->balance_callback != &balance_push_callback);
+	WARN_ON_ONCE(rq->balance_callback && rq->balance_callback != &balance_push_callback);
 # endif
 #endif
 }
@@ -2685,7 +2679,7 @@ static inline void idle_set_state(struct rq *rq,
 
 static inline struct cpuidle_state *idle_get_state(struct rq *rq)
 {
-	SCHED_WARN_ON(!rcu_read_lock_held());
+	WARN_ON_ONCE(!rcu_read_lock_held());
 
 	return rq->idle_state;
 }
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 19cdbe96f93d..452826df6ae1 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -144,7 +144,7 @@ static inline void psi_enqueue(struct task_struct *p, int flags)
 
 	if (p->se.sched_delayed) {
 		/* CPU migration of "sleeping" task */
-		SCHED_WARN_ON(!(flags & ENQUEUE_MIGRATED));
+		WARN_ON_ONCE(!(flags & ENQUEUE_MIGRATED));
 		if (p->in_memstall)
 			set |= TSK_MEMSTALL;
 		if (p->in_iowait)
-- 
2.45.2

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     f7d2728cc032a23fccb5ecde69793a38eb30ba5c
Gitweb:        https://git.kernel.org/tip/f7d2728cc032a23fccb5ecde69793a38eb30ba5c
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Mon, 17 Mar 2025 11:42:52 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 19 Mar 2025 22:20:53 +01:00

sched/debug: Change SCHED_WARN_ON() to WARN_ON_ONCE()

The scheduler has this special SCHED_WARN() facility that
depends on CONFIG_SCHED_DEBUG.

Since CONFIG_SCHED_DEBUG is getting removed, convert
SCHED_WARN() to WARN_ON_ONCE().

Note that the warning output isn't 100% equivalent:

   #define SCHED_WARN_ON(x)      WARN_ONCE(x, #x)

Because SCHED_WARN_ON() would output the 'x' condition
as well, while WARN_ONCE() will only show a backtrace.

Hopefully these are rare enough to not really matter.

If it does, we should probably introduce a new WARN_ON()
variant that outputs the condition in stringified form,
or improve WARN_ON() itself.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250317104257.3496611-2-mingo@kernel.org
---
 kernel/sched/core.c       | 24 ++++++++--------
 kernel/sched/core_sched.c |  2 +-
 kernel/sched/deadline.c   | 12 ++++----
 kernel/sched/ext.c        |  2 +-
 kernel/sched/fair.c       | 58 +++++++++++++++++++-------------------
 kernel/sched/rt.c         |  2 +-
 kernel/sched/sched.h      | 16 +++-------
 kernel/sched/stats.h      |  2 +-
 8 files changed, 56 insertions(+), 62 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index affa99f..6f666b4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -801,7 +801,7 @@ void update_rq_clock(struct rq *rq)
 
 #ifdef CONFIG_SCHED_DEBUG
 	if (sched_feat(WARN_DOUBLE_CLOCK))
-		SCHED_WARN_ON(rq->clock_update_flags & RQCF_UPDATED);
+		WARN_ON_ONCE(rq->clock_update_flags & RQCF_UPDATED);
 	rq->clock_update_flags |= RQCF_UPDATED;
 #endif
 	clock = sched_clock_cpu(cpu_of(rq));
@@ -1719,7 +1719,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
 
 	bucket = &uc_rq->bucket[uc_se->bucket_id];
 
-	SCHED_WARN_ON(!bucket->tasks);
+	WARN_ON_ONCE(!bucket->tasks);
 	if (likely(bucket->tasks))
 		bucket->tasks--;
 
@@ -1739,7 +1739,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
 	 * Defensive programming: this should never happen. If it happens,
 	 * e.g. due to future modification, warn and fix up the expected value.
 	 */
-	SCHED_WARN_ON(bucket->value > rq_clamp);
+	WARN_ON_ONCE(bucket->value > rq_clamp);
 	if (bucket->value >= rq_clamp) {
 		bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
 		uclamp_rq_set(rq, clamp_id, bkt_clamp);
@@ -2121,7 +2121,7 @@ void activate_task(struct rq *rq, struct task_struct *p, int flags)
 
 void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
 {
-	SCHED_WARN_ON(flags & DEQUEUE_SLEEP);
+	WARN_ON_ONCE(flags & DEQUEUE_SLEEP);
 
 	WRITE_ONCE(p->on_rq, TASK_ON_RQ_MIGRATING);
 	ASSERT_EXCLUSIVE_WRITER(p->on_rq);
@@ -2726,7 +2726,7 @@ __do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
 	 * XXX do further audits, this smells like something putrid.
 	 */
 	if (ctx->flags & SCA_MIGRATE_DISABLE)
-		SCHED_WARN_ON(!p->on_cpu);
+		WARN_ON_ONCE(!p->on_cpu);
 	else
 		lockdep_assert_held(&p->pi_lock);
 
@@ -4195,7 +4195,7 @@ int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 		 *  - we're serialized against set_special_state() by virtue of
 		 *    it disabling IRQs (this allows not taking ->pi_lock).
 		 */
-		SCHED_WARN_ON(p->se.sched_delayed);
+		WARN_ON_ONCE(p->se.sched_delayed);
 		if (!ttwu_state_match(p, state, &success))
 			goto out;
 
@@ -4489,7 +4489,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 	INIT_LIST_HEAD(&p->se.group_node);
 
 	/* A delayed task cannot be in clone(). */
-	SCHED_WARN_ON(p->se.sched_delayed);
+	WARN_ON_ONCE(p->se.sched_delayed);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	p->se.cfs_rq			= NULL;
@@ -5745,7 +5745,7 @@ static void sched_tick_remote(struct work_struct *work)
 			 * we are always sure that there is no proxy (only a
 			 * single task is running).
 			 */
-			SCHED_WARN_ON(rq->curr != rq->donor);
+			WARN_ON_ONCE(rq->curr != rq->donor);
 			update_rq_clock(rq);
 
 			if (!is_idle_task(curr)) {
@@ -5965,7 +5965,7 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt)
 		preempt_count_set(PREEMPT_DISABLED);
 	}
 	rcu_sleep_check();
-	SCHED_WARN_ON(ct_state() == CT_STATE_USER);
+	WARN_ON_ONCE(ct_state() == CT_STATE_USER);
 
 	profile_hit(SCHED_PROFILING, __builtin_return_address(0));
 
@@ -6811,7 +6811,7 @@ static inline void sched_submit_work(struct task_struct *tsk)
 	 * deadlock if the callback attempts to acquire a lock which is
 	 * already acquired.
 	 */
-	SCHED_WARN_ON(current->__state & TASK_RTLOCK_WAIT);
+	WARN_ON_ONCE(current->__state & TASK_RTLOCK_WAIT);
 
 	/*
 	 * If we are going to sleep and we have plugged IO queued,
@@ -9249,7 +9249,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
 	unsigned int clamps;
 
 	lockdep_assert_held(&uclamp_mutex);
-	SCHED_WARN_ON(!rcu_read_lock_held());
+	WARN_ON_ONCE(!rcu_read_lock_held());
 
 	css_for_each_descendant_pre(css, top_css) {
 		uc_parent = css_tg(css)->parent
@@ -10584,7 +10584,7 @@ static void task_mm_cid_work(struct callback_head *work)
 	struct mm_struct *mm;
 	int weight, cpu;
 
-	SCHED_WARN_ON(t != container_of(work, struct task_struct, cid_work));
+	WARN_ON_ONCE(t != container_of(work, struct task_struct, cid_work));
 
 	work->next = work;	/* Prevent double-add */
 	if (t->flags & PF_EXITING)
diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c
index 1ef98a9..c4606ca 100644
--- a/kernel/sched/core_sched.c
+++ b/kernel/sched/core_sched.c
@@ -65,7 +65,7 @@ static unsigned long sched_core_update_cookie(struct task_struct *p,
 	 * a cookie until after we've removed it, we must have core scheduling
 	 * enabled here.
 	 */
-	SCHED_WARN_ON((p->core_cookie || cookie) && !sched_core_enabled(rq));
+	WARN_ON_ONCE((p->core_cookie || cookie) && !sched_core_enabled(rq));
 
 	if (sched_core_enqueued(p))
 		sched_core_dequeue(rq, p, DEQUEUE_SAVE);
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 5dca336..d4f7cbf 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -249,8 +249,8 @@ void __add_running_bw(u64 dl_bw, struct dl_rq *dl_rq)
 
 	lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
 	dl_rq->running_bw += dl_bw;
-	SCHED_WARN_ON(dl_rq->running_bw < old); /* overflow */
-	SCHED_WARN_ON(dl_rq->running_bw > dl_rq->this_bw);
+	WARN_ON_ONCE(dl_rq->running_bw < old); /* overflow */
+	WARN_ON_ONCE(dl_rq->running_bw > dl_rq->this_bw);
 	/* kick cpufreq (see the comment in kernel/sched/sched.h). */
 	cpufreq_update_util(rq_of_dl_rq(dl_rq), 0);
 }
@@ -262,7 +262,7 @@ void __sub_running_bw(u64 dl_bw, struct dl_rq *dl_rq)
 
 	lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
 	dl_rq->running_bw -= dl_bw;
-	SCHED_WARN_ON(dl_rq->running_bw > old); /* underflow */
+	WARN_ON_ONCE(dl_rq->running_bw > old); /* underflow */
 	if (dl_rq->running_bw > old)
 		dl_rq->running_bw = 0;
 	/* kick cpufreq (see the comment in kernel/sched/sched.h). */
@@ -276,7 +276,7 @@ void __add_rq_bw(u64 dl_bw, struct dl_rq *dl_rq)
 
 	lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
 	dl_rq->this_bw += dl_bw;
-	SCHED_WARN_ON(dl_rq->this_bw < old); /* overflow */
+	WARN_ON_ONCE(dl_rq->this_bw < old); /* overflow */
 }
 
 static inline
@@ -286,10 +286,10 @@ void __sub_rq_bw(u64 dl_bw, struct dl_rq *dl_rq)
 
 	lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
 	dl_rq->this_bw -= dl_bw;
-	SCHED_WARN_ON(dl_rq->this_bw > old); /* underflow */
+	WARN_ON_ONCE(dl_rq->this_bw > old); /* underflow */
 	if (dl_rq->this_bw > old)
 		dl_rq->this_bw = 0;
-	SCHED_WARN_ON(dl_rq->running_bw > dl_rq->this_bw);
+	WARN_ON_ONCE(dl_rq->running_bw > dl_rq->this_bw);
 }
 
 static inline
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 0f1da19..953a5b9 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2341,7 +2341,7 @@ static bool task_can_run_on_remote_rq(struct task_struct *p, struct rq *rq,
 {
 	int cpu = cpu_of(rq);
 
-	SCHED_WARN_ON(task_cpu(p) == cpu);
+	WARN_ON_ONCE(task_cpu(p) == cpu);
 
 	/*
 	 * If @p has migration disabled, @p->cpus_ptr is updated to contain only
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9dafb37..89609eb 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -399,7 +399,7 @@ static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 
 static inline void assert_list_leaf_cfs_rq(struct rq *rq)
 {
-	SCHED_WARN_ON(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list);
+	WARN_ON_ONCE(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list);
 }
 
 /* Iterate through all leaf cfs_rq's on a runqueue */
@@ -696,7 +696,7 @@ static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	s64 vlag, limit;
 
-	SCHED_WARN_ON(!se->on_rq);
+	WARN_ON_ONCE(!se->on_rq);
 
 	vlag = avg_vruntime(cfs_rq) - se->vruntime;
 	limit = calc_delta_fair(max_t(u64, 2*se->slice, TICK_NSEC), se);
@@ -3317,7 +3317,7 @@ static void task_numa_work(struct callback_head *work)
 	bool vma_pids_skipped;
 	bool vma_pids_forced = false;
 
-	SCHED_WARN_ON(p != container_of(work, struct task_struct, numa_work));
+	WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work));
 
 	work->next = work;
 	/*
@@ -4036,7 +4036,7 @@ static inline bool load_avg_is_decayed(struct sched_avg *sa)
 	 * Make sure that rounding and/or propagation of PELT values never
 	 * break this.
 	 */
-	SCHED_WARN_ON(sa->load_avg ||
+	WARN_ON_ONCE(sa->load_avg ||
 		      sa->util_avg ||
 		      sa->runnable_avg);
 
@@ -5460,7 +5460,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	clear_buddies(cfs_rq, se);
 
 	if (flags & DEQUEUE_DELAYED) {
-		SCHED_WARN_ON(!se->sched_delayed);
+		WARN_ON_ONCE(!se->sched_delayed);
 	} else {
 		bool delay = sleep;
 		/*
@@ -5470,7 +5470,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 		if (flags & DEQUEUE_SPECIAL)
 			delay = false;
 
-		SCHED_WARN_ON(delay && se->sched_delayed);
+		WARN_ON_ONCE(delay && se->sched_delayed);
 
 		if (sched_feat(DELAY_DEQUEUE) && delay &&
 		    !entity_eligible(cfs_rq, se)) {
@@ -5551,7 +5551,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 	}
 
 	update_stats_curr_start(cfs_rq, se);
-	SCHED_WARN_ON(cfs_rq->curr);
+	WARN_ON_ONCE(cfs_rq->curr);
 	cfs_rq->curr = se;
 
 	/*
@@ -5592,7 +5592,7 @@ pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq)
 	if (sched_feat(PICK_BUDDY) &&
 	    cfs_rq->next && entity_eligible(cfs_rq, cfs_rq->next)) {
 		/* ->next will never be delayed */
-		SCHED_WARN_ON(cfs_rq->next->sched_delayed);
+		WARN_ON_ONCE(cfs_rq->next->sched_delayed);
 		return cfs_rq->next;
 	}
 
@@ -5628,7 +5628,7 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
 		/* in !on_rq case, update occurred at dequeue */
 		update_load_avg(cfs_rq, prev, 0);
 	}
-	SCHED_WARN_ON(cfs_rq->curr != prev);
+	WARN_ON_ONCE(cfs_rq->curr != prev);
 	cfs_rq->curr = NULL;
 }
 
@@ -5851,7 +5851,7 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
 
 			cfs_rq->throttled_clock_self = 0;
 
-			if (SCHED_WARN_ON((s64)delta < 0))
+			if (WARN_ON_ONCE((s64)delta < 0))
 				delta = 0;
 
 			cfs_rq->throttled_clock_self_time += delta;
@@ -5871,7 +5871,7 @@ static int tg_throttle_down(struct task_group *tg, void *data)
 		cfs_rq->throttled_clock_pelt = rq_clock_pelt(rq);
 		list_del_leaf_cfs_rq(cfs_rq);
 
-		SCHED_WARN_ON(cfs_rq->throttled_clock_self);
+		WARN_ON_ONCE(cfs_rq->throttled_clock_self);
 		if (cfs_rq->nr_queued)
 			cfs_rq->throttled_clock_self = rq_clock(rq);
 	}
@@ -5980,7 +5980,7 @@ done:
 	 * throttled-list.  rq->lock protects completion.
 	 */
 	cfs_rq->throttled = 1;
-	SCHED_WARN_ON(cfs_rq->throttled_clock);
+	WARN_ON_ONCE(cfs_rq->throttled_clock);
 	if (cfs_rq->nr_queued)
 		cfs_rq->throttled_clock = rq_clock(rq);
 	return true;
@@ -6136,7 +6136,7 @@ static inline void __unthrottle_cfs_rq_async(struct cfs_rq *cfs_rq)
 	}
 
 	/* Already enqueued */
-	if (SCHED_WARN_ON(!list_empty(&cfs_rq->throttled_csd_list)))
+	if (WARN_ON_ONCE(!list_empty(&cfs_rq->throttled_csd_list)))
 		return;
 
 	first = list_empty(&rq->cfsb_csd_list);
@@ -6155,7 +6155,7 @@ static void unthrottle_cfs_rq_async(struct cfs_rq *cfs_rq)
 {
 	lockdep_assert_rq_held(rq_of(cfs_rq));
 
-	if (SCHED_WARN_ON(!cfs_rq_throttled(cfs_rq) ||
+	if (WARN_ON_ONCE(!cfs_rq_throttled(cfs_rq) ||
 	    cfs_rq->runtime_remaining <= 0))
 		return;
 
@@ -6191,7 +6191,7 @@ static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b)
 			goto next;
 
 		/* By the above checks, this should never be true */
-		SCHED_WARN_ON(cfs_rq->runtime_remaining > 0);
+		WARN_ON_ONCE(cfs_rq->runtime_remaining > 0);
 
 		raw_spin_lock(&cfs_b->lock);
 		runtime = -cfs_rq->runtime_remaining + 1;
@@ -6212,7 +6212,7 @@ static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b)
 				 * We currently only expect to be unthrottling
 				 * a single cfs_rq locally.
 				 */
-				SCHED_WARN_ON(!list_empty(&local_unthrottle));
+				WARN_ON_ONCE(!list_empty(&local_unthrottle));
 				list_add_tail(&cfs_rq->throttled_csd_list,
 					      &local_unthrottle);
 			}
@@ -6237,7 +6237,7 @@ next:
 
 		rq_unlock_irqrestore(rq, &rf);
 	}
-	SCHED_WARN_ON(!list_empty(&local_unthrottle));
+	WARN_ON_ONCE(!list_empty(&local_unthrottle));
 
 	rcu_read_unlock();
 
@@ -6789,7 +6789,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
 {
 	struct sched_entity *se = &p->se;
 
-	SCHED_WARN_ON(task_rq(p) != rq);
+	WARN_ON_ONCE(task_rq(p) != rq);
 
 	if (rq->cfs.h_nr_queued > 1) {
 		u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
@@ -6900,8 +6900,8 @@ requeue_delayed_entity(struct sched_entity *se)
 	 * Because a delayed entity is one that is still on
 	 * the runqueue competing until elegibility.
 	 */
-	SCHED_WARN_ON(!se->sched_delayed);
-	SCHED_WARN_ON(!se->on_rq);
+	WARN_ON_ONCE(!se->sched_delayed);
+	WARN_ON_ONCE(!se->on_rq);
 
 	if (sched_feat(DELAY_ZERO)) {
 		update_entity_lag(cfs_rq, se);
@@ -7161,8 +7161,8 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
 		rq->next_balance = jiffies;
 
 	if (p && task_delayed) {
-		SCHED_WARN_ON(!task_sleep);
-		SCHED_WARN_ON(p->on_rq != 1);
+		WARN_ON_ONCE(!task_sleep);
+		WARN_ON_ONCE(p->on_rq != 1);
 
 		/* Fix-up what dequeue_task_fair() skipped */
 		hrtick_update(rq);
@@ -8740,7 +8740,7 @@ static inline void set_task_max_allowed_capacity(struct task_struct *p) {}
 static void set_next_buddy(struct sched_entity *se)
 {
 	for_each_sched_entity(se) {
-		if (SCHED_WARN_ON(!se->on_rq))
+		if (WARN_ON_ONCE(!se->on_rq))
 			return;
 		if (se_is_idle(se))
 			return;
@@ -12484,7 +12484,7 @@ unlock:
 
 void nohz_balance_exit_idle(struct rq *rq)
 {
-	SCHED_WARN_ON(rq != this_rq());
+	WARN_ON_ONCE(rq != this_rq());
 
 	if (likely(!rq->nohz_tick_stopped))
 		return;
@@ -12520,7 +12520,7 @@ void nohz_balance_enter_idle(int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);
 
-	SCHED_WARN_ON(cpu != smp_processor_id());
+	WARN_ON_ONCE(cpu != smp_processor_id());
 
 	/* If this CPU is going down, then nothing needs to be done: */
 	if (!cpu_active(cpu))
@@ -12603,7 +12603,7 @@ static void _nohz_idle_balance(struct rq *this_rq, unsigned int flags)
 	int balance_cpu;
 	struct rq *rq;
 
-	SCHED_WARN_ON((flags & NOHZ_KICK_MASK) == NOHZ_BALANCE_KICK);
+	WARN_ON_ONCE((flags & NOHZ_KICK_MASK) == NOHZ_BALANCE_KICK);
 
 	/*
 	 * We assume there will be no idle load after this update and clear
@@ -13043,7 +13043,7 @@ bool cfs_prio_less(const struct task_struct *a, const struct task_struct *b,
 	struct cfs_rq *cfs_rqb;
 	s64 delta;
 
-	SCHED_WARN_ON(task_rq(b)->core != rq->core);
+	WARN_ON_ONCE(task_rq(b)->core != rq->core);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	/*
@@ -13246,7 +13246,7 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
 
 static void switched_to_fair(struct rq *rq, struct task_struct *p)
 {
-	SCHED_WARN_ON(p->se.sched_delayed);
+	WARN_ON_ONCE(p->se.sched_delayed);
 
 	attach_task_cfs_rq(p);
 
@@ -13281,7 +13281,7 @@ static void __set_next_task_fair(struct rq *rq, struct task_struct *p, bool firs
 	if (!first)
 		return;
 
-	SCHED_WARN_ON(se->sched_delayed);
+	WARN_ON_ONCE(se->sched_delayed);
 
 	if (hrtick_enabled_fair(rq))
 		hrtick_start_fair(rq, p);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 8cebe71..8b8d2c1 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1713,7 +1713,7 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rt_rq *rt_rq)
 	BUG_ON(idx >= MAX_RT_PRIO);
 
 	queue = array->queue + idx;
-	if (SCHED_WARN_ON(list_empty(queue)))
+	if (WARN_ON_ONCE(list_empty(queue)))
 		return NULL;
 	next = list_entry(queue->next, struct sched_rt_entity, run_list);
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 5d853f9..fadaabe 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -91,12 +91,6 @@ struct cpuidle_state;
 #include "cpupri.h"
 #include "cpudeadline.h"
 
-#ifdef CONFIG_SCHED_DEBUG
-# define SCHED_WARN_ON(x)      WARN_ONCE(x, #x)
-#else
-# define SCHED_WARN_ON(x)      ({ (void)(x), 0; })
-#endif
-
 /* task_struct::on_rq states: */
 #define TASK_ON_RQ_QUEUED	1
 #define TASK_ON_RQ_MIGRATING	2
@@ -1571,7 +1565,7 @@ static inline void update_idle_core(struct rq *rq) { }
 
 static inline struct task_struct *task_of(struct sched_entity *se)
 {
-	SCHED_WARN_ON(!entity_is_task(se));
+	WARN_ON_ONCE(!entity_is_task(se));
 	return container_of(se, struct task_struct, se);
 }
 
@@ -1652,7 +1646,7 @@ static inline void assert_clock_updated(struct rq *rq)
 	 * The only reason for not seeing a clock update since the
 	 * last rq_pin_lock() is if we're currently skipping updates.
 	 */
-	SCHED_WARN_ON(rq->clock_update_flags < RQCF_ACT_SKIP);
+	WARN_ON_ONCE(rq->clock_update_flags < RQCF_ACT_SKIP);
 }
 
 static inline u64 rq_clock(struct rq *rq)
@@ -1699,7 +1693,7 @@ static inline void rq_clock_cancel_skipupdate(struct rq *rq)
 static inline void rq_clock_start_loop_update(struct rq *rq)
 {
 	lockdep_assert_rq_held(rq);
-	SCHED_WARN_ON(rq->clock_update_flags & RQCF_ACT_SKIP);
+	WARN_ON_ONCE(rq->clock_update_flags & RQCF_ACT_SKIP);
 	rq->clock_update_flags |= RQCF_ACT_SKIP;
 }
 
@@ -1774,7 +1768,7 @@ static inline void rq_pin_lock(struct rq *rq, struct rq_flags *rf)
 	rq->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
 	rf->clock_update_flags = 0;
 # ifdef CONFIG_SMP
-	SCHED_WARN_ON(rq->balance_callback && rq->balance_callback != &balance_push_callback);
+	WARN_ON_ONCE(rq->balance_callback && rq->balance_callback != &balance_push_callback);
 # endif
 #endif
 }
@@ -2685,7 +2679,7 @@ static inline void idle_set_state(struct rq *rq,
 
 static inline struct cpuidle_state *idle_get_state(struct rq *rq)
 {
-	SCHED_WARN_ON(!rcu_read_lock_held());
+	WARN_ON_ONCE(!rcu_read_lock_held());
 
 	return rq->idle_state;
 }
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 19cdbe9..452826d 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -144,7 +144,7 @@ static inline void psi_enqueue(struct task_struct *p, int flags)
 
 	if (p->se.sched_delayed) {
 		/* CPU migration of "sleeping" task */
-		SCHED_WARN_ON(!(flags & ENQUEUE_MIGRATED));
+		WARN_ON_ONCE(!(flags & ENQUEUE_MIGRATED));
 		if (p->in_memstall)
 			set |= TSK_MEMSTALL;
 		if (p->in_iowait)

On Thu, Mar 20, 2025 at 09:00:05AM -0000, tip-bot2 for Ingo Molnar wrote:
> The following commit has been merged into the sched/core branch of tip:
> 
> Commit-ID:     f7d2728cc032a23fccb5ecde69793a38eb30ba5c
> Gitweb:        https://git.kernel.org/tip/f7d2728cc032a23fccb5ecde69793a38eb30ba5c
> Author:        Ingo Molnar <mingo@kernel.org>
> AuthorDate:    Mon, 17 Mar 2025 11:42:52 +01:00
> Committer:     Ingo Molnar <mingo@kernel.org>
> CommitterDate: Wed, 19 Mar 2025 22:20:53 +01:00
> 
> sched/debug: Change SCHED_WARN_ON() to WARN_ON_ONCE()
> 
> The scheduler has this special SCHED_WARN() facility that
> depends on CONFIG_SCHED_DEBUG.
> 
> Since CONFIG_SCHED_DEBUG is getting removed, convert
> SCHED_WARN() to WARN_ON_ONCE().
> 
> Note that the warning output isn't 100% equivalent:
> 
>    #define SCHED_WARN_ON(x)      WARN_ONCE(x, #x)
> 
> Because SCHED_WARN_ON() would output the 'x' condition
> as well, while WARN_ONCE() will only show a backtrace.
> 
> Hopefully these are rare enough to not really matter.
> 
> If it does, we should probably introduce a new WARN_ON()
> variant that outputs the condition in stringified form,
> or improve WARN_ON() itself.

So those strings really were useful, trouble is WARN_ONCE() generates
utter crap code compared to WARN_ON_ONCE(), but since SCHED_DEBUG that
doesn't really matter.

Also, last time I measured, there was a measurable performance
difference between SCHED_DEBUG=n and SCHED_DEBUG=y.

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Thu, Mar 20, 2025 at 09:00:05AM -0000, tip-bot2 for Ingo Molnar wrote:
> > The following commit has been merged into the sched/core branch of tip:
> > 
> > Commit-ID:     f7d2728cc032a23fccb5ecde69793a38eb30ba5c
> > Gitweb:        https://git.kernel.org/tip/f7d2728cc032a23fccb5ecde69793a38eb30ba5c
> > Author:        Ingo Molnar <mingo@kernel.org>
> > AuthorDate:    Mon, 17 Mar 2025 11:42:52 +01:00
> > Committer:     Ingo Molnar <mingo@kernel.org>
> > CommitterDate: Wed, 19 Mar 2025 22:20:53 +01:00
> > 
> > sched/debug: Change SCHED_WARN_ON() to WARN_ON_ONCE()
> > 
> > The scheduler has this special SCHED_WARN() facility that
> > depends on CONFIG_SCHED_DEBUG.
> > 
> > Since CONFIG_SCHED_DEBUG is getting removed, convert
> > SCHED_WARN() to WARN_ON_ONCE().
> > 
> > Note that the warning output isn't 100% equivalent:
> > 
> >    #define SCHED_WARN_ON(x)      WARN_ONCE(x, #x)
> > 
> > Because SCHED_WARN_ON() would output the 'x' condition
> > as well, while WARN_ONCE() will only show a backtrace.
> > 
> > Hopefully these are rare enough to not really matter.
> > 
> > If it does, we should probably introduce a new WARN_ON()
> > variant that outputs the condition in stringified form,
> > or improve WARN_ON() itself.
> 
> So those strings really were useful, trouble is WARN_ONCE() generates
> utter crap code compared to WARN_ON_ONCE(), but since SCHED_DEBUG that
> doesn't really matter.

Why wouldn't it matter? CONFIG_SCHED_DEBUG was turned on for 99.9999% 
of Linux users, ie. we generated crap code for most of our users.

And as a side effect of using the standard WARN_ON_ONCE() primitive we 
now generate better code, at the expense of harder to interpret debug 
output, right?

Ie. CONFIG_SCHED_DEBUG has obfuscated crappy code generation under the 
"it's only debugging code" pretense, right?

> Also, last time I measured, there was a measurable performance
> difference between SCHED_DEBUG=n and SCHED_DEBUG=y.

Which 99.9999% of Linux users are affected by. The config option 
basically did nothing for them but hide this overhead...

Thanks,

	Ingo

* Ingo Molnar <mingo@kernel.org> wrote:

> > >    #define SCHED_WARN_ON(x)      WARN_ONCE(x, #x)
> > > 
> > > Because SCHED_WARN_ON() would output the 'x' condition
> > > as well, while WARN_ONCE() will only show a backtrace.
> > > 
> > > Hopefully these are rare enough to not really matter.
> > > 
> > > If it does, we should probably introduce a new WARN_ON()
> > > variant that outputs the condition in stringified form,
> > > or improve WARN_ON() itself.
> > 
> > So those strings really were useful, trouble is WARN_ONCE() generates
> > utter crap code compared to WARN_ON_ONCE(), but since SCHED_DEBUG that
> > doesn't really matter.
> 
> Why wouldn't it matter? CONFIG_SCHED_DEBUG was turned on for 99.9999% 
> of Linux users, ie. we generated crap code for most of our users.
> 
> And as a side effect of using the standard WARN_ON_ONCE() primitive we 
> now generate better code, at the expense of harder to interpret debug 
> output, right?
> 
> Ie. CONFIG_SCHED_DEBUG has obfuscated crappy code generation under the 
> "it's only debugging code" pretense, right?

So, to argue this via code, we'd like to have something like the patch below?

When enabled it will warn in the following fashion:

  static void super_perfect_kernel_function(void *ptr)
  {
	...
	WARN_ON_ONCE(ptr == 0 && 1);
	...
  }


  ------------[ cut here ]------------
  FAIL: 'ptr == 0 && 1' is true
  WARNING: CPU: 0 PID: 0 at kernel/sched/core.c:8511 sched_init+0x44/0x430
  ...

But the real question is, how do we keep distros from enabling 
CONFIG_DEBUG_BUGVERBOSE_EXTRA=y?

It does bloat the defconfig by about +144k .text and ~64k data, so 
maybe that's deterrence enough.

The BSS shift is due to it not using the clever x86 U2D tricks, right?

Thanks,

	Ingo

=================>
From: Ingo Molnar <mingo@kernel.org>
Date: Tue, 25 Mar 2025 11:35:20 +0100
Subject: [PATCH] bug: Introduce CONFIG_DEBUG_BUGVERBOSE_EXTRA=y to also log warning conditions

      text         data	    bss	     dec	    hex	filename
  29522704	7926322	1389904	38838930	250a292	vmlinux.before
  29667392	8017958	1363024	39048374	253d4b6	vmlinux.after

Totally-Not-Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/asm-generic/bug.h |  7 +++++++
 kernel/sched/core.c       |  2 ++
 lib/Kconfig.debug         | 12 ++++++++++++
 3 files changed, 21 insertions(+)

diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 387720933973..5475258a99dc 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -92,6 +92,11 @@ void warn_slowpath_fmt(const char *file, const int line, unsigned taint,
 		       const char *fmt, ...);
 extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
 
+#ifdef CONFIG_DEBUG_BUGVERBOSE_EXTRA
+#define WARN_ON_ONCE(condition)						\
+	DO_ONCE_LITE_IF(condition, WARN, 1, "FAIL: '%s' is true", #condition)
+#endif
+
 #ifndef __WARN_FLAGS
 #define __WARN()		__WARN_printf(TAINT_WARN, NULL)
 #define __WARN_printf(taint, arg...) do {				\
@@ -107,6 +112,7 @@ extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
 		__WARN_FLAGS(BUGFLAG_NO_CUT_HERE | BUGFLAG_TAINT(taint));\
 		instrumentation_end();					\
 	} while (0)
+#ifndef WARN_ON_ONCE
 #define WARN_ON_ONCE(condition) ({				\
 	int __ret_warn_on = !!(condition);			\
 	if (unlikely(__ret_warn_on))				\
@@ -115,6 +121,7 @@ extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
 	unlikely(__ret_warn_on);				\
 })
 #endif
+#endif
 
 /* used internally by panic.c */
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 87540217fc09..71bf94bf68f8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8508,6 +8508,8 @@ void __init sched_init(void)
 	unsigned long ptr = 0;
 	int i;
 
+	WARN_ON_ONCE(ptr == 0 && 1);
+
 	/* Make sure the linker didn't screw up */
 #ifdef CONFIG_SMP
 	BUG_ON(!sched_class_above(&stop_sched_class, &dl_sched_class));
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index b1b92a9a8f24..88f215f712f8 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -206,6 +206,18 @@ config DEBUG_BUGVERBOSE
 	  of the BUG call as well as the EIP and oops trace.  This aids
 	  debugging but costs about 70-100K of memory.
 
+config DEBUG_BUGVERBOSE_EXTRA
+	bool "Extra verbose WARN_ON() reporting" if DEBUG_BUGVERBOSE
+	default n
+	help
+	  Say Y here to make WARN_ON() warnings extra verbose, printing
+	  the condition they warn about.
+
+	  This aids debugging but uses up some memory and causes some
+	  runtime overhead due to worse code generation.
+
+	  If unsure, say N.
+
 endmenu # "printk and dmesg options"
 
 config DEBUG_KERNEL

On Tue, Mar 25, 2025 at 12:18:39PM +0100, Ingo Molnar wrote:

> So, to argue this via code, we'd like to have something like the patch below?

I would do it differently. If we know the thing is a simple string, we
can stick it in bug_entry and print from __report_bug() without causing
horrific shite at the call site.

The problem with WARN() is that it is a format string, which must be
filled out in situ. Resulting in calls to snprintf() and arguments and
whatnot.

 On Tue, 25 Mar 2025 at 05:36, Peter Zijlstra <peterz@infradead.org> wrote:
>
> The problem with WARN() is that it is a format string, which must be
> filled out in situ. Resulting in calls to snprintf() and arguments and
> whatnot.

A fair number of warnings do want the format string, so that you can
print out more information about what went wrong if the warning
triggered.

That said, I do think that the "just give a fixed string that is the
warning condition" is probably the right thing 90% of the time, and is
the much simpler interface both to use and causes much less code
(exactly because it's just a single hardcoded string at compile time).

So I think we end up wanting both.

But I *don't* like Ingo's suggestion of DEBUG_BUGVERBOSE_EXTRA,
because it does that "both" by making the simple case complicated.

How about going a different route instead? Right now we have that
CONFIG_DEBUG_BUGVERBOSE thing which adds the file name and line number
information. That has been very good.

But maybe that should be extended to also always take the compile-time
'#condition' string?

So then all warnings would have the warning condition string (assuming
you end up enabling DEBUG_BUGVERBOSE, of course, which I think
everybody pretty much does). With no extra code.

And then the _dynamic_ string - and associated code generation - would
be only for when you want to print out the actual values that caused
the warning.

Hmm?

             Linus

On Tue, Mar 25, 2025 at 10:48:49AM -0700, Linus Torvalds wrote:
> Hmm?

That is indeed what I was thinking of; far better articulated :-)

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> How about going a different route instead? Right now we have that 
> CONFIG_DEBUG_BUGVERBOSE thing which adds the file name and line 
> number information. That has been very good.
> 
> But maybe that should be extended to also always take the 
> compile-time '#condition' string?
> 
> So then all warnings would have the warning condition string 
> (assuming you end up enabling DEBUG_BUGVERBOSE, of course, which I 
> think everybody pretty much does). With no extra code.

So something like the patch below?

Testcase:

  @@ -8508,6 +8508,8 @@ void __init sched_init(void)
          unsigned long ptr = 0;
          int i;
 
  +       WARN_ON_ONCE(ptr == 0 && 1);
  +

Before:

  WARNING: CPU: 0 PID: 0 at kernel/sched/core.c:8511 sched_init+0x20/0x410

After:

  WARNING: CPU: 0 PID: 0 at [ptr == 0 && 1] kernel/sched/core.c:8511 sched_init+0x20/0x410
                            ^^^^^^^^^^^^^^^

I concatenated the condition string with the file string, so didn't 
have to extend the 'struct bug_entry' backend, and could be shared with 
the regular WARN() and BUG*() code as well without modifying its 
output.

The .text impact is zero, as hoped for:

       text       data        bss         dec        hex    filename
   29523998    7926322    1389904    38840224    250a7a0    vmlinux.before
   29523998    8024626    1389904    38938528    25227a0    vmlinue.after

So this does have the debugging advantages of SCHED_WARN_ON() and the 
code generation benefits of WARN_ON_ONCE().

Note that the patch has still the maturity of a Labradoodle puppy: it 
won't build on the majority of non-x86 architectures, has only been 
built and booted once, etc. - so it's not signed off on.

Thanks,

	Ingo

===================>
From: Ingo Molnar <mingo@kernel.org>
Date: Tue, 25 Mar 2025 12:18:44 +0100
Subject: [PATCH] bug: Add the condition string to the CONFIG_DEBUG_BUGVERBOSE=y output

       text       data        bss         dec        hex    filename
   29523998    7926322    1389904    38840224    250a7a0    vmlinux.before
   29523998    8024626    1389904    38938528    25227a0    vmlinue.after

Before:

  WARNING: CPU: 0 PID: 0 at kernel/sched/core.c:8511 sched_init+0x20/0x410

After:

  WARNING: CPU: 0 PID: 0 at [ptr == 0 && 1] kernel/sched/core.c:8511 sched_init+0x20/0x410
                            ^^^^^^^^^^^^^^^
Not-Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/Z-KRD3ODxT9f8Yjw@gmail.com
---
 arch/x86/include/asm/bug.h | 14 +++++++-------
 include/asm-generic/bug.h  |  7 ++++---
 kernel/sched/core.c        |  2 ++
 3 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index f0e9acf72547..e966199c8ef7 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -39,7 +39,7 @@
 
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 
-#define _BUG_FLAGS(ins, flags, extra)					\
+#define _BUG_FLAGS(cond_str, ins, flags, extra)				\
 do {									\
 	asm_inline volatile("1:\t" ins "\n"				\
 		     ".pushsection __bug_table,\"aw\"\n"		\
@@ -50,14 +50,14 @@ do {									\
 		     "\t.org 2b+%c3\n"					\
 		     ".popsection\n"					\
 		     extra						\
-		     : : "i" (__FILE__), "i" (__LINE__),		\
+		     : : "i" (cond_str __FILE__), "i" (__LINE__),		\
 			 "i" (flags),					\
 			 "i" (sizeof(struct bug_entry)));		\
 } while (0)
 
 #else /* !CONFIG_DEBUG_BUGVERBOSE */
 
-#define _BUG_FLAGS(ins, flags, extra)					\
+#define _BUG_FLAGS(cond_str, ins, flags, extra)				\
 do {									\
 	asm_inline volatile("1:\t" ins "\n"				\
 		     ".pushsection __bug_table,\"aw\"\n"		\
@@ -74,7 +74,7 @@ do {									\
 
 #else
 
-#define _BUG_FLAGS(ins, flags, extra)  asm volatile(ins)
+#define _BUG_FLAGS(cond_str, ins, flags, extra)  asm volatile(ins)
 
 #endif /* CONFIG_GENERIC_BUG */
 
@@ -82,7 +82,7 @@ do {									\
 #define BUG()							\
 do {								\
 	instrumentation_begin();				\
-	_BUG_FLAGS(ASM_UD2, 0, "");				\
+	_BUG_FLAGS("", ASM_UD2, 0, "");				\
 	__builtin_unreachable();				\
 } while (0)
 
@@ -92,11 +92,11 @@ do {								\
  * were to trigger, we'd rather wreck the machine in an attempt to get the
  * message out than not know about it.
  */
-#define __WARN_FLAGS(flags)					\
+#define __WARN_FLAGS(cond_str, flags)				\
 do {								\
 	__auto_type __flags = BUGFLAG_WARNING|(flags);		\
 	instrumentation_begin();				\
-	_BUG_FLAGS(ASM_UD2, __flags, ANNOTATE_REACHABLE(1b));	\
+	_BUG_FLAGS(cond_str, ASM_UD2, __flags, ANNOTATE_REACHABLE(1b)); \
 	instrumentation_end();					\
 } while (0)
 
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 387720933973..c8e7126bc26e 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -100,17 +100,18 @@ extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
 		instrumentation_end();					\
 	} while (0)
 #else
-#define __WARN()		__WARN_FLAGS(BUGFLAG_TAINT(TAINT_WARN))
+#define __WARN()		__WARN_FLAGS("", BUGFLAG_TAINT(TAINT_WARN))
 #define __WARN_printf(taint, arg...) do {				\
 		instrumentation_begin();				\
 		__warn_printk(arg);					\
-		__WARN_FLAGS(BUGFLAG_NO_CUT_HERE | BUGFLAG_TAINT(taint));\
+		__WARN_FLAGS("", BUGFLAG_NO_CUT_HERE | BUGFLAG_TAINT(taint));\
 		instrumentation_end();					\
 	} while (0)
 #define WARN_ON_ONCE(condition) ({				\
 	int __ret_warn_on = !!(condition);			\
 	if (unlikely(__ret_warn_on))				\
-		__WARN_FLAGS(BUGFLAG_ONCE |			\
+		__WARN_FLAGS("["#condition"] ",			\
+			     BUGFLAG_ONCE |			\
 			     BUGFLAG_TAINT(TAINT_WARN));	\
 	unlikely(__ret_warn_on);				\
 })
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 87540217fc09..71bf94bf68f8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8508,6 +8508,8 @@ void __init sched_init(void)
 	unsigned long ptr = 0;
 	int i;
 
+	WARN_ON_ONCE(ptr == 0 && 1);
+
 	/* Make sure the linker didn't screw up */
 #ifdef CONFIG_SMP
 	BUG_ON(!sched_class_above(&stop_sched_class, &dl_sched_class));

On Tue, 25 Mar 2025 at 15:42, Ingo Molnar <mingo@kernel.org> wrote:
>
> So something like the patch below?
> [...]
> After:
>
>   WARNING: CPU: 0 PID: 0 at [ptr == 0 && 1] kernel/sched/core.c:8511 sched_init+0x20/0x410
>                             ^^^^^^^^^^^^^^^

Hmm. Is that the prettiest output ever? No. But it does seem workable,
and the patch is simple.

And I think the added condition string is useful, in that I often end
up looking up warnings that other people report and where the line
numbers have changed enough that it's not immediately obvious exactly
which warning it is. Not only does it disambiguate which warning it
is, it would probably often would obviate having to look it up
entirely because the warning message is now more useful.

So I think I like it. Let's see how it works in practice.

(I actually think the "CPU: 0 PID: 0" is likely the least useful part
of that warning string, and maybe *that* should be moved away and make
things a bit more legible, but I think that discussion might as well
be part of that "Let's see how it works")

            Linus

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Tue, 25 Mar 2025 at 15:42, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > So something like the patch below?
> > [...]
> > After:
> >
> >   WARNING: CPU: 0 PID: 0 at [ptr == 0 && 1] kernel/sched/core.c:8511 sched_init+0x20/0x410
> >                             ^^^^^^^^^^^^^^^
> 
> Hmm. Is that the prettiest output ever? No. But it does seem workable,
> and the patch is simple.
> 
> And I think the added condition string is useful, in that I often end
> up looking up warnings that other people report and where the line
> numbers have changed enough that it's not immediately obvious exactly
> which warning it is. Not only does it disambiguate which warning it
> is, it would probably often would obviate having to look it up
> entirely because the warning message is now more useful.

Yeah, that exactly was the original motivation for SCHED_WARN_ON(): 
core kernel code often gets backported on and changed by distributions, 
so line numbers are fuzzy and with large functions it's sometimes 
unclear exactly where the warning originated from.

> So I think I like it. Let's see how it works in practice.
> 
> (I actually think the "CPU: 0 PID: 0" is likely the least useful part 
> of that warning string, and maybe *that* should be moved away and 
> make things a bit more legible, but I think that discussion might as 
> well be part of that "Let's see how it works")

Okay!

The CPU and PID part is particularly useless, given that it's repeated 
in the splat a few lines later:

  ------------[ cut here ]------------^M
  WARNING: CPU: 0 PID: 0 at [ptr == 0 && 1] kernel/sched/core.c:8511 sched_init+0x20/0x410
  Modules linked in:
  CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.14.0-01616-g94d7af2844aa #4 PREEMPT(undef)
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
  RIP: 0010:sched_init+0x20/0x410

So I'll just remove it, which will turn this into:

  WARNING: [ptr == 0 && 1] kernel/sched/core.c:8511 sched_init+0x20/0x410

Which is actually pretty nicely formatted IMHO and orders the 
information by expected entropy: most constant, most valuable 
information comes first.

BTW., there's also another option we still have open: by using a unique 
character separator that isn't 0 we could split up the single string 
into cond_str and FILE_str parts, and leave formatting to 
architectures. But I don't think it's needed if we get rid of the "CPU: 
PID:" noise though.

	Ingo