From: Juri Lelli juri.lelli@redhat.com
commit 2279f540ea7d05f22d2f0c4224319330228586bc upstream.
Glenn reported that "an application [he developed produces] a BUG in deadline.c when a SCHED_DEADLINE task contends with CFS tasks on nested PTHREAD_PRIO_INHERIT mutexes. I believe the bug is triggered when a CFS task that was boosted by a SCHED_DEADLINE task boosts another CFS task (nested priority inheritance).
------------[ cut here ]------------ kernel BUG at kernel/sched/deadline.c:1462! invalid opcode: 0000 [#1] PREEMPT SMP CPU: 12 PID: 19171 Comm: dl_boost_bug Tainted: ... Hardware name: ... RIP: 0010:enqueue_task_dl+0x335/0x910 Code: ... RSP: 0018:ffffc9000c2bbc68 EFLAGS: 00010002 RAX: 0000000000000009 RBX: ffff888c0af94c00 RCX: ffffffff81e12500 RDX: 000000000000002e RSI: ffff888c0af94c00 RDI: ffff888c10b22600 RBP: ffffc9000c2bbd08 R08: 0000000000000009 R09: 0000000000000078 R10: ffffffff81e12440 R11: ffffffff81e1236c R12: ffff888bc8932600 R13: ffff888c0af94eb8 R14: ffff888c10b22600 R15: ffff888bc8932600 FS: 00007fa58ac55700(0000) GS:ffff888c10b00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fa58b523230 CR3: 0000000bf44ab003 CR4: 00000000007606e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: ? intel_pstate_update_util_hwp+0x13/0x170 rt_mutex_setprio+0x1cc/0x4b0 task_blocks_on_rt_mutex+0x225/0x260 rt_spin_lock_slowlock_locked+0xab/0x2d0 rt_spin_lock_slowlock+0x50/0x80 hrtimer_grab_expiry_lock+0x20/0x30 hrtimer_cancel+0x13/0x30 do_nanosleep+0xa0/0x150 hrtimer_nanosleep+0xe1/0x230 ? __hrtimer_init_sleeper+0x60/0x60 __x64_sys_nanosleep+0x8d/0xa0 do_syscall_64+0x4a/0x100 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x7fa58b52330d ... ---[ end trace 0000000000000002 ]—
He also provided a simple reproducer creating the situation below:
So the execution order of locking steps are the following (N1 and N2 are non-deadline tasks. D1 is a deadline task. M1 and M2 are mutexes that are enabled * with priority inheritance.)
Time moves forward as this timeline goes down:
N1 N2 D1 | | | | | | Lock(M1) | | | | | | Lock(M2) | | | | | | Lock(M2) | | | | Lock(M1) | | (!!bug triggered!) |
Daniel reported a similar situation as well, by just letting ksoftirqd run with DEADLINE (and eventually block on a mutex).
Problem is that boosted entities (Priority Inheritance) use static DEADLINE parameters of the top priority waiter. However, there might be cases where top waiter could be a non-DEADLINE entity that is currently boosted by a DEADLINE entity from a different lock chain (i.e., nested priority chains involving entities of non-DEADLINE classes). In this case, top waiter static DEADLINE parameters could be null (initialized to 0 at fork()) and replenish_dl_entity() would hit a BUG().
Fix this by keeping track of the original donor and using its parameters when a task is boosted.
Reported-by: Glenn Elliott glenn@aurora.tech Reported-by: Daniel Bristot de Oliveira bristot@redhat.com Signed-off-by: Juri Lelli juri.lelli@redhat.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Tested-by: Daniel Bristot de Oliveira bristot@redhat.com Link: https://lkml.kernel.org/r/20201117061432.517340-1-juri.lelli@redhat.com [Ankit: Regenerated the patch for v5.4.y] Signed-off-by: Ankit Jain ankitja@vmware.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/sched.h | 10 ++++ kernel/sched/core.c | 11 ++--- kernel/sched/deadline.c | 97 ++++++++++++++++++++++++++---------------------- 3 files changed, 68 insertions(+), 50 deletions(-)
--- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -544,7 +544,6 @@ struct sched_dl_entity { * overruns. */ unsigned int dl_throttled : 1; - unsigned int dl_boosted : 1; unsigned int dl_yielded : 1; unsigned int dl_non_contending : 1; unsigned int dl_overrun : 1; @@ -563,6 +562,15 @@ struct sched_dl_entity { * time. */ struct hrtimer inactive_timer; + +#ifdef CONFIG_RT_MUTEXES + /* + * Priority Inheritance. When a DEADLINE scheduling entity is boosted + * pi_se points to the donor, otherwise points to the dl_se it belongs + * to (the original one/itself). + */ + struct sched_dl_entity *pi_se; +#endif };
#ifdef CONFIG_UCLAMP_TASK --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4554,20 +4554,21 @@ void rt_mutex_setprio(struct task_struct if (!dl_prio(p->normal_prio) || (pi_task && dl_prio(pi_task->prio) && dl_entity_preempt(&pi_task->dl, &p->dl))) { - p->dl.dl_boosted = 1; + p->dl.pi_se = pi_task->dl.pi_se; queue_flag |= ENQUEUE_REPLENISH; - } else - p->dl.dl_boosted = 0; + } else { + p->dl.pi_se = &p->dl; + } p->sched_class = &dl_sched_class; } else if (rt_prio(prio)) { if (dl_prio(oldprio)) - p->dl.dl_boosted = 0; + p->dl.pi_se = &p->dl; if (oldprio < prio) queue_flag |= ENQUEUE_HEAD; p->sched_class = &rt_sched_class; } else { if (dl_prio(oldprio)) - p->dl.dl_boosted = 0; + p->dl.pi_se = &p->dl; if (rt_prio(oldprio)) p->rt.timeout = 0; p->sched_class = &fair_sched_class; --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -43,6 +43,28 @@ static inline int on_dl_rq(struct sched_ return !RB_EMPTY_NODE(&dl_se->rb_node); }
+#ifdef CONFIG_RT_MUTEXES +static inline struct sched_dl_entity *pi_of(struct sched_dl_entity *dl_se) +{ + return dl_se->pi_se; +} + +static inline bool is_dl_boosted(struct sched_dl_entity *dl_se) +{ + return pi_of(dl_se) != dl_se; +} +#else +static inline struct sched_dl_entity *pi_of(struct sched_dl_entity *dl_se) +{ + return dl_se; +} + +static inline bool is_dl_boosted(struct sched_dl_entity *dl_se) +{ + return false; +} +#endif + #ifdef CONFIG_SMP static inline struct dl_bw *dl_bw_of(int i) { @@ -657,7 +679,7 @@ static inline void setup_new_dl_entity(s struct dl_rq *dl_rq = dl_rq_of_se(dl_se); struct rq *rq = rq_of_dl_rq(dl_rq);
- WARN_ON(dl_se->dl_boosted); + WARN_ON(is_dl_boosted(dl_se)); WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
/* @@ -695,21 +717,20 @@ static inline void setup_new_dl_entity(s * could happen are, typically, a entity voluntarily trying to overcome its * runtime, or it just underestimated it during sched_setattr(). */ -static void replenish_dl_entity(struct sched_dl_entity *dl_se, - struct sched_dl_entity *pi_se) +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_se->dl_runtime <= 0); + BUG_ON(pi_of(dl_se)->dl_runtime <= 0);
/* * This could be the case for a !-dl task that is boosted. * Just go with full inherited parameters. */ if (dl_se->dl_deadline == 0) { - dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline; - dl_se->runtime = pi_se->dl_runtime; + dl_se->deadline = rq_clock(rq) + pi_of(dl_se)->dl_deadline; + dl_se->runtime = pi_of(dl_se)->dl_runtime; }
if (dl_se->dl_yielded && dl_se->runtime > 0) @@ -722,8 +743,8 @@ static void replenish_dl_entity(struct s * arbitrary large. */ while (dl_se->runtime <= 0) { - dl_se->deadline += pi_se->dl_period; - dl_se->runtime += pi_se->dl_runtime; + dl_se->deadline += pi_of(dl_se)->dl_period; + dl_se->runtime += pi_of(dl_se)->dl_runtime; }
/* @@ -737,8 +758,8 @@ static void replenish_dl_entity(struct s */ if (dl_time_before(dl_se->deadline, rq_clock(rq))) { printk_deferred_once("sched: DL replenish lagged too much\n"); - dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline; - dl_se->runtime = pi_se->dl_runtime; + dl_se->deadline = rq_clock(rq) + pi_of(dl_se)->dl_deadline; + dl_se->runtime = pi_of(dl_se)->dl_runtime; }
if (dl_se->dl_yielded) @@ -771,8 +792,7 @@ static void replenish_dl_entity(struct s * task with deadline equal to period this is the same of using * dl_period instead of dl_deadline in the equation above. */ -static bool dl_entity_overflow(struct sched_dl_entity *dl_se, - struct sched_dl_entity *pi_se, u64 t) +static bool dl_entity_overflow(struct sched_dl_entity *dl_se, u64 t) { u64 left, right;
@@ -794,9 +814,9 @@ static bool dl_entity_overflow(struct sc * of anything below microseconds resolution is actually fiction * (but still we want to give the user that illusion >;). */ - left = (pi_se->dl_deadline >> DL_SCALE) * (dl_se->runtime >> DL_SCALE); + left = (pi_of(dl_se)->dl_deadline >> DL_SCALE) * (dl_se->runtime >> DL_SCALE); right = ((dl_se->deadline - t) >> DL_SCALE) * - (pi_se->dl_runtime >> DL_SCALE); + (pi_of(dl_se)->dl_runtime >> DL_SCALE);
return dl_time_before(right, left); } @@ -881,24 +901,23 @@ static inline bool dl_is_implicit(struct * Please refer to the comments update_dl_revised_wakeup() function to find * more about the Revised CBS rule. */ -static void update_dl_entity(struct sched_dl_entity *dl_se, - struct sched_dl_entity *pi_se) +static void update_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);
if (dl_time_before(dl_se->deadline, rq_clock(rq)) || - dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) { + dl_entity_overflow(dl_se, rq_clock(rq))) {
if (unlikely(!dl_is_implicit(dl_se) && !dl_time_before(dl_se->deadline, rq_clock(rq)) && - !dl_se->dl_boosted)){ + !is_dl_boosted(dl_se))) { update_dl_revised_wakeup(dl_se, rq); return; }
- dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline; - dl_se->runtime = pi_se->dl_runtime; + dl_se->deadline = rq_clock(rq) + pi_of(dl_se)->dl_deadline; + dl_se->runtime = pi_of(dl_se)->dl_runtime; } }
@@ -997,7 +1016,7 @@ static enum hrtimer_restart dl_task_time * The task might have been boosted by someone else and might be in the * boosting/deboosting path, its not throttled. */ - if (dl_se->dl_boosted) + if (is_dl_boosted(dl_se)) goto unlock;
/* @@ -1025,7 +1044,7 @@ static enum hrtimer_restart dl_task_time * but do not enqueue -- wait for our wakeup to do that. */ if (!task_on_rq_queued(p)) { - replenish_dl_entity(dl_se, dl_se); + replenish_dl_entity(dl_se); goto unlock; }
@@ -1115,7 +1134,7 @@ static inline void dl_check_constrained_
if (dl_time_before(dl_se->deadline, rq_clock(rq)) && dl_time_before(rq_clock(rq), dl_next_period(dl_se))) { - if (unlikely(dl_se->dl_boosted || !start_dl_timer(p))) + if (unlikely(is_dl_boosted(dl_se) || !start_dl_timer(p))) return; dl_se->dl_throttled = 1; if (dl_se->runtime > 0) @@ -1246,7 +1265,7 @@ throttle: dl_se->dl_overrun = 1;
__dequeue_task_dl(rq, curr, 0); - if (unlikely(dl_se->dl_boosted || !start_dl_timer(curr))) + if (unlikely(is_dl_boosted(dl_se) || !start_dl_timer(curr))) enqueue_task_dl(rq, curr, ENQUEUE_REPLENISH);
if (!is_leftmost(curr, &rq->dl)) @@ -1440,8 +1459,7 @@ static void __dequeue_dl_entity(struct s }
static void -enqueue_dl_entity(struct sched_dl_entity *dl_se, - struct sched_dl_entity *pi_se, int flags) +enqueue_dl_entity(struct sched_dl_entity *dl_se, int flags) { BUG_ON(on_dl_rq(dl_se));
@@ -1452,9 +1470,9 @@ enqueue_dl_entity(struct sched_dl_entity */ if (flags & ENQUEUE_WAKEUP) { task_contending(dl_se, flags); - update_dl_entity(dl_se, pi_se); + update_dl_entity(dl_se); } else if (flags & ENQUEUE_REPLENISH) { - replenish_dl_entity(dl_se, pi_se); + replenish_dl_entity(dl_se); } else if ((flags & ENQUEUE_RESTORE) && dl_time_before(dl_se->deadline, rq_clock(rq_of_dl_rq(dl_rq_of_se(dl_se))))) { @@ -1471,19 +1489,7 @@ static void dequeue_dl_entity(struct sch
static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags) { - struct task_struct *pi_task = rt_mutex_get_top_task(p); - struct sched_dl_entity *pi_se = &p->dl; - - /* - * Use the scheduling parameters of the top pi-waiter task if: - * - we have a top pi-waiter which is a SCHED_DEADLINE task AND - * - our dl_boosted is set (i.e. the pi-waiter's (absolute) deadline is - * smaller than our deadline OR we are a !SCHED_DEADLINE task getting - * boosted due to a SCHED_DEADLINE pi-waiter). - * Otherwise we keep our runtime and deadline. - */ - if (pi_task && dl_prio(pi_task->normal_prio) && p->dl.dl_boosted) { - pi_se = &pi_task->dl; + if (is_dl_boosted(&p->dl)) { /* * Because of delays in the detection of the overrun of a * thread's runtime, it might be the case that a thread @@ -1516,7 +1522,7 @@ static void enqueue_task_dl(struct rq *r * the throttle. */ p->dl.dl_throttled = 0; - BUG_ON(!p->dl.dl_boosted || flags != ENQUEUE_REPLENISH); + BUG_ON(!is_dl_boosted(&p->dl) || flags != ENQUEUE_REPLENISH); return; }
@@ -1553,7 +1559,7 @@ static void enqueue_task_dl(struct rq *r return; }
- enqueue_dl_entity(&p->dl, pi_se, flags); + enqueue_dl_entity(&p->dl, flags);
if (!task_current(rq, p) && p->nr_cpus_allowed > 1) enqueue_pushable_dl_task(rq, p); @@ -2722,11 +2728,14 @@ void __dl_clear_params(struct task_struc dl_se->dl_bw = 0; dl_se->dl_density = 0;
- dl_se->dl_boosted = 0; dl_se->dl_throttled = 0; dl_se->dl_yielded = 0; dl_se->dl_non_contending = 0; dl_se->dl_overrun = 0; + +#ifdef CONFIG_RT_MUTEXES + dl_se->pi_se = dl_se; +#endif }
bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr)