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

diff --git a/kernel/sched/autogroup.c b/kernel/sched/autogroup.c
index 4ebaf97f7bd8576b31a27f3836535e264a42b007..991fc90025357964edf8d64a361a843e926160c1 100644 (file)
--- a/kernel/sched/autogroup.c
+++ b/kernel/sched/autogroup.c
@@ -161,7 +161,8 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag)
        struct task_struct *t;
        unsigned long flags;
 
-       BUG_ON(!lock_task_sighand(p, &flags));
+       if (WARN_ON_ONCE(!lock_task_sighand(p, &flags)))
+               return;
 
        prev = p->signal->autogroup;
        if (prev == ag) {

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ee28253c9ac0c2ed4e602a9584b5e1a77c4f2825..813687a5f5cf266e016fda01c73bef3bfc966bae 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2328,7 +2328,7 @@ static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
        rq = cpu_rq(new_cpu);
 
        rq_lock(rq, rf);
-       BUG_ON(task_cpu(p) != new_cpu);
+       WARN_ON_ONCE(task_cpu(p) != new_cpu);
        activate_task(rq, p, 0);
        check_preempt_curr(rq, p, 0);
 

diff --git a/kernel/sched/cpupri.c b/kernel/sched/cpupri.c
index fa9ce9d836839df6cb220d70c7b2dc1f11fb344d..a286e726eb4b857d12f2a03b2cadfa07d0df9e52 100644 (file)
--- a/kernel/sched/cpupri.c
+++ b/kernel/sched/cpupri.c
@@ -147,7 +147,7 @@ int cpupri_find_fitness(struct cpupri *cp, struct task_struct *p,
        int task_pri = convert_prio(p->prio);
        int idx, cpu;
 
-       BUG_ON(task_pri >= CPUPRI_NR_PRIORITIES);
+       WARN_ON_ONCE(task_pri >= CPUPRI_NR_PRIORITIES);
 
        for (idx = 0; idx < task_pri; idx++) {
 

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0ab79d819a0d64f0b533683605b914d8b9398443..962b169b05cf4cdf66dd94bfe97c8728dbe2a5de 100644 (file)
--- 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;

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 914096c5b1ae1eae09e4fde0b0c859f3dbdf3ae6..28f10dccd1944806300c34182f8f4cbdcf32c65f 100644 (file)
--- 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();

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 55f39c8f42032817f8be1c1304c0585903dfbd5b..2936fe55cef796e51b0aaa57dafb159ff4865bdc 100644 (file)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -843,7 +843,7 @@ static void __disable_runtime(struct rq *rq)
                 * We cannot be left wanting - that would mean some runtime
                 * leaked out of the system.
                 */
-               BUG_ON(want);
+               WARN_ON_ONCE(want);
 balanced:
                /*
                 * Disable all the borrow logic by pretending we have inf

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e26688d387aebe3588b9175de20f3b646c7fd8e3..7a44dceeb50a106b066843a15e98bb53b1e0e56e 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2709,8 +2709,8 @@ static inline void double_rq_lock(struct rq *rq1, struct rq *rq2)
        __acquires(rq1->lock)
        __acquires(rq2->lock)
 {
-       BUG_ON(!irqs_disabled());
-       BUG_ON(rq1 != rq2);
+       WARN_ON_ONCE(!irqs_disabled());
+       WARN_ON_ONCE(rq1 != rq2);
        raw_spin_rq_lock(rq1);
        __acquire(rq2->lock);   /* Fake it out ;) */
        double_rq_clock_clear_update(rq1, rq2);
@@ -2726,7 +2726,7 @@ static inline void double_rq_unlock(struct rq *rq1, struct rq *rq2)
        __releases(rq1->lock)
        __releases(rq2->lock)
 {
-       BUG_ON(rq1 != rq2);
+       WARN_ON_ONCE(rq1 != rq2);
        raw_spin_rq_unlock(rq1);
        __release(rq2->lock);
 }