Messages in this thread Patch in this message | | | From | Hao Jia <> | Subject | [PATCH] sched/core: Avoid obvious double update_rq_clock warning | Date | Mon, 18 Apr 2022 17:09:29 +0800 |
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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 cores, the core rq->clock_update_flags may be RQCF_UPDATED at this time, and then calling update_rq_clock will trigger 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
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 tasks that periodically change the priority and sleep, e.g.:
void *ThreadFun(void *arg) { int cnt = *(int*)arg; struct sched_param param;
while (1) { sqrt(MAGIC_NUM); cnt = cnt % 10 + 1; param.sched_priority = cnt; pthread_setschedparam(pthread_self(), SCHED_RR, ¶m); sqrt(MAGIC_NUM); sqrt(MAGIC_NUM); sleep(cnt); } return NULL; }
Signed-off-by: Hao Jia <jiahao.os@bytedance.com> --- kernel/sched/deadline.c | 18 +++++++++++------- kernel/sched/rt.c | 20 ++++++++++++++++++-- 2 files changed, 29 insertions(+), 9 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index fb4255ae0b2c..9207b978cc43 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2258,6 +2258,7 @@ static int push_dl_task(struct rq *rq) { struct task_struct *next_task; struct rq *later_rq; + struct rq_flags srf, drf; int ret = 0; if (!rq->dl.overloaded) @@ -2317,16 +2318,14 @@ static int push_dl_task(struct rq *rq) goto retry; } + rq_pin_lock(rq, &srf); + rq_pin_lock(later_rq, &drf); deactivate_task(rq, next_task, 0); set_task_cpu(next_task, later_rq->cpu); - - /* - * Update the later_rq clock here, because the clock is used - * by the cpufreq_update_util() inside __add_running_bw(). - */ - update_rq_clock(later_rq); - activate_task(later_rq, next_task, ENQUEUE_NOCLOCK); + activate_task(later_rq, next_task, 0); ret = 1; + rq_unpin_lock(rq, &srf); + rq_unpin_lock(later_rq, &drf); resched_curr(later_rq); @@ -2351,6 +2350,7 @@ static void pull_dl_task(struct rq *this_rq) struct task_struct *p, *push_task; bool resched = false; struct rq *src_rq; + struct rq_flags this_rf, src_rf; u64 dmin = LONG_MAX; if (likely(!dl_overloaded(this_rq))) @@ -2413,11 +2413,15 @@ static void pull_dl_task(struct rq *this_rq) if (is_migration_disabled(p)) { push_task = get_push_task(src_rq); } else { + rq_pin_lock(this_rq, &this_rf); + rq_pin_lock(src_rq, &src_rf); deactivate_task(src_rq, p, 0); set_task_cpu(p, this_cpu); activate_task(this_rq, p, 0); dmin = p->dl.deadline; resched = true; + rq_unpin_lock(this_rq, &this_rf); + rq_unpin_lock(src_rq, &src_rf); } /* Is there any other task even earlier? */ diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index a32c46889af8..9305ad87fef0 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -871,6 +871,7 @@ 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; /* @@ -885,7 +886,7 @@ 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) { @@ -923,7 +924,7 @@ 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)) @@ -2001,6 +2002,7 @@ static int push_rt_task(struct rq *rq, bool pull) { struct task_struct *next_task; struct rq *lowest_rq; + struct rq_flags srf, drf; int ret = 0; if (!rq->rt.overloaded) @@ -2102,9 +2104,18 @@ static int push_rt_task(struct rq *rq, bool pull) goto retry; } + /* + * We may drop rq'lock in double_lock_balance, + * so we still need to clean up the RQCF_UPDATED flag + * to avoid the WARN_DOUBLE_CLOCK warning. + */ + rq_pin_lock(rq, &srf); + rq_pin_lock(lowest_rq, &drf); deactivate_task(rq, next_task, 0); set_task_cpu(next_task, lowest_rq->cpu); activate_task(lowest_rq, next_task, 0); + rq_unpin_lock(rq, &srf); + rq_unpin_lock(lowest_rq, &drf); resched_curr(lowest_rq); ret = 1; @@ -2299,6 +2310,7 @@ static void pull_rt_task(struct rq *this_rq) bool resched = false; struct task_struct *p, *push_task; struct rq *src_rq; + struct rq_flags src_rf, this_rf; int rt_overload_count = rt_overloaded(this_rq); if (likely(!rt_overload_count)) @@ -2375,10 +2387,14 @@ static void pull_rt_task(struct rq *this_rq) if (is_migration_disabled(p)) { push_task = get_push_task(src_rq); } else { + rq_pin_lock(this_rq, &this_rf); + rq_pin_lock(src_rq, &src_rf); deactivate_task(src_rq, p, 0); set_task_cpu(p, this_cpu); activate_task(this_rq, p, 0); resched = true; + rq_unpin_lock(this_rq, &this_rf); + rq_unpin_lock(src_rq, &src_rf); } /* * We continue with the search, just in -- 2.32.0
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