sched/deadline: Fix priority inheritance with multiple scheduling classes

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

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0e91b451d2a241c9d0dfd7ccf55b399797849fbb..095fdec07b385c1c0d18a10feb2cd57e0add0719 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -551,7 +551,6 @@ 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;
@@ -570,6 +569,15 @@ 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

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9f0ebfb0d17bd1931b8894ceee3b57106964391a..e7e453492cffc0082ef11ba3e826257f6324db35 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4912,20 +4912,21 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
                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;

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 6d93f451873493e9c0e61e749b462f0ca62e1d58..949bc5c083c136b5f36d6ee038387219179e8411 100644 (file)
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -43,6 +43,28 @@ static inline int on_dl_rq(struct sched_dl_entity *dl_se)
        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)
 {
@@ -698,7 +720,7 @@ static inline void setup_new_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);
 
-       WARN_ON(dl_se->dl_boosted);
+       WARN_ON(is_dl_boosted(dl_se));
        WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
 
        /*
@@ -736,21 +758,20 @@ static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
  * 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)
@@ -763,8 +784,8 @@ static void replenish_dl_entity(struct sched_dl_entity *dl_se,
         * 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;
        }
 
        /*
@@ -778,8 +799,8 @@ static void replenish_dl_entity(struct sched_dl_entity *dl_se,
         */
        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)
@@ -812,8 +833,7 @@ static void replenish_dl_entity(struct sched_dl_entity *dl_se,
  * 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;
 
@@ -835,9 +855,9 @@ static bool dl_entity_overflow(struct sched_dl_entity *dl_se,
         * 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);
 }
@@ -922,24 +942,23 @@ static inline bool dl_is_implicit(struct sched_dl_entity *dl_se)
  * 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;
        }
 }
 
@@ -1038,7 +1057,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
         * 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;
 
        /*
@@ -1066,7 +1085,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
         * 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;
        }
 
@@ -1156,7 +1175,7 @@ static inline void dl_check_constrained_dl(struct sched_dl_entity *dl_se)
 
        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)
@@ -1287,7 +1306,7 @@ 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))
@@ -1481,8 +1500,7 @@ static void __dequeue_dl_entity(struct sched_dl_entity *dl_se)
 }
 
 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));
 
@@ -1493,9 +1511,9 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se,
         */
        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))))) {
@@ -1512,19 +1530,7 @@ static void dequeue_dl_entity(struct sched_dl_entity *dl_se)
 
 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
@@ -1557,7 +1563,7 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
                 * 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;
        }
 
@@ -1594,7 +1600,7 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
                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);
@@ -2787,11 +2793,14 @@ void __dl_clear_params(struct task_struct *p)
        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)