From: Hao Jia jiahao.os@bytedance.com
[ Upstream commit 2679a83731d51a744657f718fc02c3b077e47562 ]
When we use raw_spin_rq_lock() to acquire the rq lock and have to update the rq clock while holding the lock, the kernel may issue a WARN_DOUBLE_CLOCK warning.
Since we directly use raw_spin_rq_lock() to acquire rq lock instead of rq_lock(), there is no corresponding change to rq->clock_update_flags. In particular, we have obtained the rq lock of other CPUs, the rq->clock_update_flags of this CPU may be RQCF_UPDATED at this time, and then calling update_rq_clock() will trigger the WARN_DOUBLE_CLOCK warning.
So we need to clear RQCF_UPDATED of rq->clock_update_flags to avoid the WARN_DOUBLE_CLOCK warning.
For the sched_rt_period_timer() and migrate_task_rq_dl() cases we simply replace raw_spin_rq_lock()/raw_spin_rq_unlock() with rq_lock()/rq_unlock().
For the {pull,push}_{rt,dl}_task() cases, we add the double_rq_clock_clear_update() function to clear RQCF_UPDATED of rq->clock_update_flags, and call double_rq_clock_clear_update() before double_lock_balance()/double_rq_lock() returns to avoid the WARN_DOUBLE_CLOCK warning.
Some call trace reports: Call Trace 1: <IRQ> sched_rt_period_timer+0x10f/0x3a0 ? enqueue_top_rt_rq+0x110/0x110 __hrtimer_run_queues+0x1a9/0x490 hrtimer_interrupt+0x10b/0x240 __sysvec_apic_timer_interrupt+0x8a/0x250 sysvec_apic_timer_interrupt+0x9a/0xd0 </IRQ> <TASK> asm_sysvec_apic_timer_interrupt+0x12/0x20
Call Trace 2: <TASK> activate_task+0x8b/0x110 push_rt_task.part.108+0x241/0x2c0 push_rt_tasks+0x15/0x30 finish_task_switch+0xaa/0x2e0 ? __switch_to+0x134/0x420 __schedule+0x343/0x8e0 ? hrtimer_start_range_ns+0x101/0x340 schedule+0x4e/0xb0 do_nanosleep+0x8e/0x160 hrtimer_nanosleep+0x89/0x120 ? hrtimer_init_sleeper+0x90/0x90 __x64_sys_nanosleep+0x96/0xd0 do_syscall_64+0x34/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae
Call Trace 3: <TASK> deactivate_task+0x93/0xe0 pull_rt_task+0x33e/0x400 balance_rt+0x7e/0x90 __schedule+0x62f/0x8e0 do_task_dead+0x3f/0x50 do_exit+0x7b8/0xbb0 do_group_exit+0x2d/0x90 get_signal+0x9df/0x9e0 ? preempt_count_add+0x56/0xa0 ? __remove_hrtimer+0x35/0x70 arch_do_signal_or_restart+0x36/0x720 ? nanosleep_copyout+0x39/0x50 ? do_nanosleep+0x131/0x160 ? audit_filter_inodes+0xf5/0x120 exit_to_user_mode_prepare+0x10f/0x1e0 syscall_exit_to_user_mode+0x17/0x30 do_syscall_64+0x40/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae
Call Trace 4: update_rq_clock+0x128/0x1a0 migrate_task_rq_dl+0xec/0x310 set_task_cpu+0x84/0x1e4 try_to_wake_up+0x1d8/0x5c0 wake_up_process+0x1c/0x30 hrtimer_wakeup+0x24/0x3c __hrtimer_run_queues+0x114/0x270 hrtimer_interrupt+0xe8/0x244 arch_timer_handler_phys+0x30/0x50 handle_percpu_devid_irq+0x88/0x140 generic_handle_domain_irq+0x40/0x60 gic_handle_irq+0x48/0xe0 call_on_irq_stack+0x2c/0x60 do_interrupt_handler+0x80/0x84
Steps to reproduce: 1. Enable CONFIG_SCHED_DEBUG when compiling the kernel 2. echo 1 > /sys/kernel/debug/clear_warn_once echo "WARN_DOUBLE_CLOCK" > /sys/kernel/debug/sched/features echo "NO_RT_PUSH_IPI" > /sys/kernel/debug/sched/features 3. Run some rt/dl tasks that periodically work and sleep, e.g. Create 2*n rt or dl (90% running) tasks via rt-app (on a system with n CPUs), and Dietmar Eggemann reports Call Trace 4 when running on PREEMPT_RT kernel.
Signed-off-by: Hao Jia jiahao.os@bytedance.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Dietmar Eggemann dietmar.eggemann@arm.com Link: https://lore.kernel.org/r/20220430085843.62939-2-jiahao.os@bytedance.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 6 +++--- kernel/sched/deadline.c | 5 +++-- kernel/sched/rt.c | 5 +++-- kernel/sched/sched.h | 28 ++++++++++++++++++++++++---- 4 files changed, 33 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 1eec4925b8c6..a6722496ed5f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -546,10 +546,10 @@ void double_rq_lock(struct rq *rq1, struct rq *rq2) swap(rq1, rq2);
raw_spin_rq_lock(rq1); - if (__rq_lockp(rq1) == __rq_lockp(rq2)) - return; + if (__rq_lockp(rq1) != __rq_lockp(rq2)) + raw_spin_rq_lock_nested(rq2, SINGLE_DEPTH_NESTING);
- raw_spin_rq_lock_nested(rq2, SINGLE_DEPTH_NESTING); + double_rq_clock_clear_update(rq1, rq2); } #endif
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 62f0cf842277..1571b775ec15 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1804,6 +1804,7 @@ select_task_rq_dl(struct task_struct *p, int cpu, int flags)
static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused) { + struct rq_flags rf; struct rq *rq;
if (READ_ONCE(p->__state) != TASK_WAKING) @@ -1815,7 +1816,7 @@ static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused * from try_to_wake_up(). Hence, p->pi_lock is locked, but * rq->lock is not... So, lock it */ - raw_spin_rq_lock(rq); + rq_lock(rq, &rf); if (p->dl.dl_non_contending) { update_rq_clock(rq); sub_running_bw(&p->dl, &rq->dl); @@ -1831,7 +1832,7 @@ static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused put_task_struct(p); } sub_rq_bw(&p->dl, &rq->dl); - raw_spin_rq_unlock(rq); + rq_unlock(rq, &rf); }
static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 14f273c29518..3b8a7e153367 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -885,6 +885,7 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun) int enqueue = 0; struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i); struct rq *rq = rq_of_rt_rq(rt_rq); + struct rq_flags rf; int skip;
/* @@ -899,7 +900,7 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun) if (skip) continue;
- raw_spin_rq_lock(rq); + rq_lock(rq, &rf); update_rq_clock(rq);
if (rt_rq->rt_time) { @@ -937,7 +938,7 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
if (enqueue) sched_rt_rq_enqueue(rt_rq); - raw_spin_rq_unlock(rq); + rq_unlock(rq, &rf); }
if (!throttled && (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index e8a5549488dd..3887f4aea160 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2494,6 +2494,24 @@ unsigned long arch_scale_freq_capacity(int cpu) } #endif
+#ifdef CONFIG_SCHED_DEBUG +/* + * In double_lock_balance()/double_rq_lock(), we use raw_spin_rq_lock() to + * acquire rq lock instead of rq_lock(). So at the end of these two functions + * we need to call double_rq_clock_clear_update() to clear RQCF_UPDATED of + * rq->clock_update_flags to avoid the WARN_DOUBLE_CLOCK warning. + */ +static inline void double_rq_clock_clear_update(struct rq *rq1, struct rq *rq2) +{ + rq1->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP); + /* rq1 == rq2 for !CONFIG_SMP, so just clear RQCF_UPDATED once. */ +#ifdef CONFIG_SMP + rq2->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP); +#endif +} +#else +static inline void double_rq_clock_clear_update(struct rq *rq1, struct rq *rq2) {} +#endif
#ifdef CONFIG_SMP
@@ -2559,14 +2577,15 @@ static inline int _double_lock_balance(struct rq *this_rq, struct rq *busiest) __acquires(busiest->lock) __acquires(this_rq->lock) { - if (__rq_lockp(this_rq) == __rq_lockp(busiest)) - return 0; - - if (likely(raw_spin_rq_trylock(busiest))) + if (__rq_lockp(this_rq) == __rq_lockp(busiest) || + likely(raw_spin_rq_trylock(busiest))) { + double_rq_clock_clear_update(this_rq, busiest); return 0; + }
if (rq_order_less(this_rq, busiest)) { raw_spin_rq_lock_nested(busiest, SINGLE_DEPTH_NESTING); + double_rq_clock_clear_update(this_rq, busiest); return 0; }
@@ -2660,6 +2679,7 @@ static inline void double_rq_lock(struct rq *rq1, struct rq *rq2) BUG_ON(rq1 != rq2); raw_spin_rq_lock(rq1); __acquire(rq2->lock); /* Fake it out ;) */ + double_rq_clock_clear_update(rq1, rq2); }
/*