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Message-Id: <20220418090929.54005-1-jiahao.os@bytedance.com>
Date: Mon, 18 Apr 2022 17:09:29 +0800
From: Hao Jia <jiahao.os@...edance.com>
To: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
vincent.guittot@...aro.org, dietmar.eggemann@....com,
rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
bristot@...hat.com
Cc: linux-kernel@...r.kernel.org, Hao Jia <jiahao.os@...edance.com>
Subject: [PATCH] sched/core: Avoid obvious double update_rq_clock warning
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@...edance.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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